start work on 2.0.19-SNAPSHOT

Signed-off-by: ceki <ceki@qos.ch>

README.md

@@ -2,31 +2,33 @@
 
 The Simple Logging Facade for Java (SLF4J) serves as a simple facade
 or abstraction for various logging frameworks (e.g. java.util.logging,
-logback, reload4j, log4j 2.x) allowing the end user to plug in the desired logging
-framework at deployment time.
+logback, reload4j, log4j 2.x, logevents, penna, rainbowgum, tinylog)
+allowing the end user to plug in the desired logging framework at
+deployment time.
 
 More information can be found on the [SLF4J website](http://www.slf4j.org).
 
-# Build Status
-[![Build Status](https://travis-ci.org/qos-ch/slf4j.svg)](https://travis-ci.org/qos-ch/slf4j)
-
 # Search org.slf4j artifacts on Maven Central
-[![Maven Central](https://img.shields.io/badge/Search%20org%2Eslf4j%20artifacts%20on%20Maven%20Central-2.0.x-green)](https://search.maven.org/search?q=g:org.slf4j%20AND%20v:2.0.%3F) 
+[![Maven Central](https://img.shields.io/badge/Search%20org%2Eslf4j%20artifacts%20on%20Maven%20Central-2.0.x-green)](https://central.sonatype.com/search?namespace=org.slf4j) 
 
 
 # In case of problems
 
 In case of problems please do not hesitate to post an e-mail message
-on the slf4j-user@qos.ch mailing list.  However, please do not
-directly e-mail SLF4J developers. The answer to your question might
-be useful to other users. Moreover, there are many knowledgeable users
-on the slf4j-user mailing lists who can quickly answer your
-questions.
+on the [slf4j-user@qos.ch](https://mailman.qos.ch/cgi-bin/mailman/listinfo/slf4j-user)
+mailing list or to start a <a
+href="https://github.com/qos-ch/slf4j/discussions">discussion</a> on
+github.  However, please do not directly e-mail SLF4J developers. The
+answer to your question might be useful to other users. Moreover,
+there are many knowledgeable users on the slf4j-user mailing lists who
+can quickly answer your questions.
 
 # Urgent issues
 
-For urgent issues do not hesitate to [champion a release](https://github.com/sponsors/qos-ch/sponsorships?tier_id=77436).
-In principle, most championed issues are solved within 3 business days ensued by a release.
+For urgent issues do not hesitate to [champion a
+release](https://github.com/sponsors/qos-ch/sponsorships?tier_id=77436).
+In principle, most championed issues are solved within 3 business days
+ensued by a release.
 
 # How to build SLF4J
 
@@ -43,14 +45,13 @@ process:
 1. Start a discussion on the [slf4j-dev mailing
 list](http://www.slf4j.org/mailing-lists.html) about your proposed
 change. Alternately, file a [bug
-report](http://www.slf4j.org/bug-reporting.html) to initiate the
-discussion. Note that we ask pull requests to be linked to a [Jira
-ticket](https://jira.qos.ch/).
+report](https://github.com/qos-ch/slf4j/issues) on github to initiate the
+discussion. 
 
 2. Fork qos-ch/slf4j. Ideally, create a new branch from your fork for
 your contribution to make it easier to merge your changes back.
 
-3. Make your changes on the branch you hopefully created in Step 2. Be
+3. Make your changes on the branch created in Step 2. Be
 sure that your code passes existing unit tests. Please add unit tests
 for your work if appropriate. It usually is.
 
@@ -61,10 +62,8 @@ will be automatically rejected by the [DCO GitHub
 check](https://probot.github.io/apps/dco/) application.
 
 5. Push your changes to your fork/branch in GitHub. Don't push it to
-your master! If you do it will make it harder to submit new changes
+your master! If you do, it will make it harder to submit new changes
 later.
 
 6. Submit a pull request to SLF4J from your commit page on GitHub.
 
-7. Did we mention that you will be asked to link your pull request
-with a Jira ticket?

integration/build.xml

@@ -82,12 +82,12 @@
 	</target>
 
 	<target name="testAll" depends="init, 
-		        testNoProvider150,
+		            testNoProvider150,
                 testMismatch,
                 testMatch,
-		        testMultiBinding,                
-                testFuture_16Series,
-                testActiveSecurityManager">
+		            testMultiBinding,
+                testFuture_16Series"
+                >
 	</target>
 
 
@@ -201,7 +201,7 @@
     <property name="path_to_policy" value="file:./src/policy/java-under-ant.policy"/>
   </target>
 
-
+  <!-- no longer supported in JDK 24 and later -->
 	<target name="testActiveSecurityManager" depends="setPathToPolicy_FromTop, setPathToPolicy_FromIntegration">
 		<junit printsummary="yes" fork="no" haltonfailure="yes">
       <jvmarg value="-Djava.security.manager"/>

integration/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

integration/src/test/java/org/slf4j/CompatibilityAssertionTest.java

@@ -27,6 +27,7 @@ package org.slf4j;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.slf4j.helpers.Reporter.SLF4J_INTERNAL_VERBOSITY_KEY;
 
 import java.io.PrintStream;
 import java.util.Random;
@@ -43,11 +44,13 @@ public class CompatibilityAssertionTest {
 
     @Before
     public void setUp() throws Exception {
+        System.setProperty(SLF4J_INTERNAL_VERBOSITY_KEY, "debug");
         System.setErr(sps);
     }
 
     @After
     public void tearDown() throws Exception {
+        System.clearProperty(SLF4J_INTERNAL_VERBOSITY_KEY);
         System.setErr(old);
     }
 
@@ -56,9 +59,13 @@ public class CompatibilityAssertionTest {
         Logger logger = LoggerFactory.getLogger(this.getClass());
         String msg = "hello world " + diff;
         logger.info(msg);
-        assertEquals(1, sps.stringList.size());
+        assertEquals(2, sps.stringList.size());
+
         String s0 = (String) sps.stringList.get(0);
-        assertTrue(s0.contains(msg));
+        assertTrue(s0.startsWith("SLF4J(D): Connected with provider of type [org.slf4j.simple.SimpleServiceProvider]"));
+
+        String s1 = (String) sps.stringList.get(1);
+        assertTrue(s1.contains(msg));
 
     }
 }

integration/src/test/java/org/slf4j/MultiBindingAssertionTest.java

@@ -55,11 +55,13 @@ public class MultiBindingAssertionTest {
         String msg = "hello world " + diff;
         logger.info(msg);
         List<String> list = sps.stringList;
-        assertMsgContains(list, 0, "Class path contains multiple SLF4J providers.");
-        assertMsgContains(list, 1, "Found provider");
-        assertMsgContains(list, 2, "Found provider");
-        assertMsgContains(list, 3, "See https://www.slf4j.org/codes.html#multiple_bindings for an explanation.");
-        assertMsgContains(list, 4, "Actual provider is of type [");
+        int line = 0;
+
+        assertMsgContains(list, line++, "Class path contains multiple SLF4J providers.");
+        assertMsgContains(list, line++, "Found provider");
+        assertMsgContains(list, line++, "Found provider");
+        assertMsgContains(list, line++, "See https://www.slf4j.org/codes.html#multiple_bindings for an explanation.");
+        //assertMsgContains(list, line++, "SLF4J(D): Connected with provider of type [");
     }
 
     void assertMsgContains(List<String> strList, int index, String msg) {

jcl-over-slf4j/pom.xml

@@ -5,7 +5,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 
@@ -19,7 +19,7 @@
 
   <licenses>
     <license>
-      <name>Apache License, Version 2.0</name>
+      <name>Apache-2.0</name>
       <url>https://www.apache.org/licenses/LICENSE-2.0.txt</url>
       <distribution>repo</distribution>
     </license>

jul-to-slf4j/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

log4j-over-slf4j/compatibility/build.xml

@@ -1,137 +0,0 @@
-<project name="testing-log4j-bridge" default="usage" basedir=".">
-
-	<property name="lbversion" value="0.9.8-SNAPSHOT" />
-    <property name="slf4jversion" value="1.4.2" />
-	<property name="source.home" value="./src/main/java/" />
-	<property name="javac.dest.12" value="./target/classes12/" />
-	<property name="javac.dest.13" value="./target/classes13/" />
-	<property name="lib" value="./lib" />
-
-	<property name="deprecation" value="on" />
-
-	<path id="basic.classpath">
-		<pathelement location="${source.home}" />
-		<pathelement location="${lib}/junit-3.8.1.jar" />
-	</path>
-
-	<path id="log4j12.classpath">
-		<path refid="basic.classpath" />
-		<pathelement location="${javac.dest.12}" />
-		<pathelement location="${lib}/log4j-1.2.14.jar" />
-	</path>
-
-	<path id="log4j13.classpath">
-		<path refid="basic.classpath" />
-		<pathelement location="${javac.dest.13}" />
-		<pathelement location="${lib}/log4j-1.3alpha-8.jar" />
-	</path>
-
-	<path id="los.classpath">
-		<path refid="basic.classpath" />
-		<pathelement location="${lib}/log4j-over-slf4j-${slf4jversion}.jar" />
-		<pathelement location="${lib}/logback-classic-${lbversion}.jar" />
-		<pathelement location="${lib}/logback-core-${lbversion}.jar" />
-		<pathelement location="${lib}/slf4j-api-${slf4jversion}.jar" />
-	</path>
-
-	<!-- ================================================================= -->
-	<!-- Default target                                                    -->
-	<!-- ================================================================= -->
-	<target name="usage">
-		<echo>      
-      These are some of the targets supported by this ANT build script:
-
-      all - run all available tests
-      refresh - copy required jar files to the lib directory
-    </echo>
-	</target>
-
-  <delete>
-    <fileset dir="." includes="**/*.bak"/>
-  </delete>
-
-  <target name="refresh">
-    <delete>
-      <fileset dir="lib">
-        <include name="logback-*.jar"/>
-        <include name="log4j-bridge-*.jar"/>
-      </fileset>
-    </delete>
-    <copy file="../../slf4j-api/target/slf4j-api-${slf4jversion}.jar" todir="lib/"/>
-    <copy file="../target/log4j-over-slf4j-${slf4jversion}.jar" todir="lib/"/>
-
-  </target>
-
-
-	<target name="init">
-		<mkdir dir="${javac.dest.12}" />
-		<mkdir dir="${javac.dest.13}" />
-	</target>
-
-	<target name="clean">
-		<delete>
-			<fileset dir="${javac.dest.12}" includes="**" />
-			<fileset dir="${javac.dest.13}" includes="**" />
-		</delete>
-	</target>
-
-	<target name="build_log4j12" depends="init">
-		<javac srcdir="${source.home}" 
-			     destdir="${javac.dest.12}" 
-			     includes="**/Log4j12Calls.java" 
-			     deprecation="${deprecation}" debug="on">
-			<classpath refid="log4j12.classpath" />
-		</javac>
-	</target>
-
-	<target name="build_log4j13" depends="init">
-		<javac srcdir="${source.home}" 
-			     destdir="${javac.dest.13}" 
-			     includes="**/Log4j13Calls.java" deprecation="${deprecation}" debug="on">
-			<classpath refid="log4j13.classpath" />
-		</javac>
-	</target>
-	
-	<target name="build_loggerTest" depends="init">
-		<javac srcdir="${source.home}" 
-			     destdir="${javac.dest.12}" 
-			     includes="**/LoggerTest.java" 
-			     deprecation="${deprecation}" debug="on">
-			<classpath refid="los.classpath" />
-		</javac>
-	</target>
-
-	<!-- ================================================================= -->
-	<!-- Run tests                                                     -->
-	<!-- ================================================================= -->
-	<target name="all" depends="test12, test13, loggerTest" />
-
-
-	<target name="loggerTest" depends="build_loggerTest">
-		<junit printsummary="yes" fork="yes" haltonfailure="yes">
-			<classpath refid="los.classpath" />
-			<classpath location="${javac.dest.12}" />
-			<formatter type="plain" usefile="false" />
-			<test name="test.LoggerTest" />
-		</junit>
-	</target>
-	
-	<target name="test12" depends="build_log4j12">
-		<junit printsummary="yes" fork="yes" haltonfailure="yes">
-			<classpath refid="los.classpath" />
-			<classpath location="${javac.dest.12}" />
-			<formatter type="plain" usefile="false" />
-			<test name="test.Log4j12Calls" />
-		</junit>
-	</target>
-
-	<target name="test13" depends="build_log4j13">
-		<junit printsummary="yes" fork="yes" haltonfailure="yes">
-			<classpath refid="los.classpath" />
-			<classpath location="${javac.dest.13}" />
-			<formatter type="plain" usefile="false" />
-			<test name="test.Log4j13Calls" />
-		</junit>
-	</target>
-
-</project>

log4j-over-slf4j/compatibility/readme.txt

@@ -1,17 +0,0 @@
-
-This directory is used to test the module against various log4j calls. 
-Two test cases simulate the typical calls that one can find in an application 
-that uses either log4j 1.2.x, or log4j 1.3.x.
-
-In the same directory is a build.xml file that uses ant to 
-compile the test cases with the corresponding log4j version, 
-and to run these tests without log4j in the classpath but with
-logback jars instead.
-
-To run the tests, one must have ant installed. Issuing the following command, 
-once in the compatibility directory will launch the tests:
-
-ant all
-
-To obtain more information about the use of the log4j-over-slf4j module, 
-please visit http://www.slf4j.org/log4j-over-slf4j.html

log4j-over-slf4j/compatibility/src/main/java/test/DummyObject.java

@@ -1,8 +0,0 @@
-package test;
-
-public class DummyObject {
-
-  public String toString() {
-    return "dummy";
-  }
-}

log4j-over-slf4j/compatibility/src/main/java/test/Log4j12Calls.java

@@ -1,39 +0,0 @@
-/**
- * Logback: the reliable, generic, fast and flexible logging framework.
- * 
- * Copyright (C) 1999-2006, QOS.ch
- * 
- * This library is free software, you can redistribute it and/or modify it under
- * the terms of the GNU Lesser General Public License as published by the Free
- * Software Foundation.
- */
-package test;
-
-import junit.framework.TestCase;
-
-import org.apache.log4j.Logger;
-import org.apache.log4j.MDC;
-
-/**
- * 
- * A test case that issues the typical calls
- * that an application using log4j 1.2 would do.
- *
- * @author Ceki Gülcü
- * @author Sébastien Pennec
- */
-public class Log4j12Calls extends TestCase {
-  public static final Logger logger = Logger.getLogger(Log4j12Calls.class);
-  
-  public void testLog() {
-    MDC.put("key", "value1");
-    
-    logger.trace("Trace level can be noisy");
-    logger.debug("Entering application");
-    logger.info("Violets are blue");
-    logger.warn("Here is a warning");
-    logger.error("Exiting application", new Exception("just testing"));
-    
-    MDC.remove("key");
-  }
-}

log4j-over-slf4j/compatibility/src/main/java/test/Log4j13Calls.java

@@ -1,46 +0,0 @@
-/**
- * Logback: the reliable, generic, fast and flexible logging framework.
- * 
- * Copyright (C) 1999-2006, QOS.ch
- * 
- * This library is free software, you can redistribute it and/or modify it under
- * the terms of the GNU Lesser General Public License as published by the Free
- * Software Foundation.
- */
-
-package test;
-
-import junit.framework.TestCase;
-
-import org.apache.log4j.Logger;
-import org.apache.log4j.MDC;
-
-/**
- * 
- * A test case that issues the typical calls
- * that an application using log4j 1.3 would do.
- *
- * @author Ceki Gülcü
- * @author Sébastien Pennec
- */
-
-public class Log4j13Calls extends TestCase {
-  public static final Logger logger = Logger.getLogger(Log4j12Calls.class);
-  
-  public void testLog() {
-    MDC.put("key", "value1");
-    
-    logger.trace("Trace level can be noisy");
-    logger.debug("Entering application");
-    logger.info("Violets are blue");
-    logger.warn("Here is a warning");
-    logger.info("The answer is {}.", new Integer(42));
-    logger.info("Number: {} and another one: {}.", new Integer(42), new Integer(24));
-    
-    logger.error("Exiting application", new Exception("just testing"));
-    
-    MDC.remove("key");
-    
-    MDC.clear();
-  }
-}

log4j-over-slf4j/compatibility/src/main/java/test/LoggerTest.java

@@ -1,169 +0,0 @@
-package test;
-
-import junit.framework.TestCase;
-
-import org.slf4j.LoggerFactory;
-
-import ch.qos.logback.classic.LoggerContext;
-import ch.qos.logback.classic.spi.LoggingEvent;
-import ch.qos.logback.core.read.ListAppender;
-import org.apache.log4j.Level;
-
-/**
- * A class that tests the invocation of the org.apache.log4j.Logger class that
- * belongs to the log4j-bridge package
- * 
- * @author Sébastien Pennec
- * @author Ceki Gülcü
- */
-
-public class LoggerTest extends TestCase {
-
-  LoggerContext context;
-  ListAppender<LoggingEvent> appender;
-  ch.qos.logback.classic.Logger logbackLogger;
-  org.apache.log4j.Logger log4jLogger;
-
-  public void setUp() throws Exception {
-    context = (LoggerContext) LoggerFactory.getILoggerFactory();
-    context.shutdownAndReset();
-    appender = new ListAppender<LoggingEvent>();
-    appender.setContext(context);
-    appender.setName("listAppender");
-    appender.start();
-    ch.qos.logback.classic.Logger lbLogger = context
-        .getLogger(LoggerContext.ROOT_NAME);
-    lbLogger.addAppender(appender);
-
-    log4jLogger = org.apache.log4j.Logger.getLogger(LoggerTest.class);
-    logbackLogger = context.getLogger(LoggerTest.class);
-    super.setUp();
-  }
-
-  public void tearDown() throws Exception {
-    appender.stop();
-    context.stop();
-    appender = null;
-    context = null;
-    logbackLogger = null; 
-    log4jLogger = null;
-    super.tearDown();
-  }
-
-  public void testLogWithObjectMessages() {
-    LoggingEvent event;
-
-    log4jLogger.debug("test");
-    event = appender.list.get(0);
-    assertEquals("test", event.getMessage());
-    appender.list.clear();
-
-    log4jLogger.debug(null);
-    event = appender.list.get(0);
-    assertEquals(null, event.getMessage());
-    appender.list.clear();
-
-    DummyObject dummy = new DummyObject();
-    log4jLogger.debug(dummy);
-    event = appender.list.get(0);
-    assertEquals(dummy.toString(), event.getMessage());
-    appender.list.clear();
-  }
-
-  public void testIsEnabledAPI() {
-    assertFalse(log4jLogger.isTraceEnabled());
-    assertTrue(log4jLogger.isDebugEnabled());
-    assertTrue(log4jLogger.isInfoEnabled());
-    assertTrue(log4jLogger.isWarnEnabled());
-    assertTrue(log4jLogger.isErrorEnabled());
-  }
-
-  public void testPrintAPI() {
-    Exception e = new Exception("just testing");
-
-    log4jLogger.trace(null);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-    
-    log4jLogger.debug(null);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.debug("debug message");
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.info(null);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.info("info  message");
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.warn(null);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.warn("warn message");
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.error(null);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.error("error message");
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.debug(null, e);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.debug("debug message", e);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.info(null, e);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.info("info  message", e);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.warn(null, e);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.warn("warn message", e);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.error(null, e);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-    log4jLogger.error("error message", e);
-    assertEquals(1, appender.list.size());
-    appender.list.clear();
-
-  }
-  
-  public void testLogAPI() {
-    log4jLogger.log("x", Level.TRACE, "x", null);
-    assertEquals(0, appender.list.size());
-
-    log4jLogger.log("x", Level.DEBUG, "x", null);
-    log4jLogger.log("x", Level.INFO, "x", null);
-    log4jLogger.log("x", Level.WARN, "x", null);
-    log4jLogger.log("x", Level.ERROR, "x", null);
-    log4jLogger.log("x", Level.FATAL, "x", null);
-
-    assertEquals(5, appender.list.size());
-    appender.list.clear();
-
-  }
-
-}

log4j-over-slf4j/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 
@@ -21,8 +21,8 @@
 
   <licenses>
     <license>
-      <name>Apache Software Licenses</name>
-      <url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
+      <name>Apache-2.0</name>
+      <url>https://www.apache.org/licenses/LICENSE-2.0.txt</url>
     </license>
   </licenses>
 

osgi-over-slf4j/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

parent/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-bom</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
@@ -24,10 +24,9 @@
   <inceptionYear>2005</inceptionYear>
 
 
-
   <properties>
     <!-- yyyy-MM-dd'T'HH:mm:ss'Z' -->
-    <project.build.outputTimestamp>2023-09-03T16:20:19Z</project.build.outputTimestamp>
+    <project.build.outputTimestamp>2026-05-12T18:37:04Z</project.build.outputTimestamp>
     <latest.1.version>1.7.36</latest.1.version>
     <!-- java.util.ServiceLoader requires Java 6 -->
     <jdk.version>8</jdk.version>
@@ -38,14 +37,14 @@
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
     <!-- used in integration testing -->
     <cal10n.version>0.8.1</cal10n.version>
-    <reload4j.version>1.2.22</reload4j.version>    
+    <reload4j.version>1.2.22</reload4j.version>
     <logback.version>1.2.10</logback.version>
     <jcl.version>1.2</jcl.version>
     <junit.version>4.13.1</junit.version>
     <maven-site-plugin.version>3.7.1</maven-site-plugin.version>
     <maven-compiler-plugin.version>3.10.1</maven-compiler-plugin.version>
     <maven-surefire-plugin.version>3.0.0-M7</maven-surefire-plugin.version>
-    <maven-javadoc-plugin.version>3.5.0</maven-javadoc-plugin.version>
+    <maven-javadoc-plugin.version>3.6.3</maven-javadoc-plugin.version>
     <maven-source-plugin.version>3.2.1</maven-source-plugin.version>
     <maven-deploy-plugin.version>3.0.0-M1</maven-deploy-plugin.version>
     <maven-jar-plugin.version>3.2.0</maven-jar-plugin.version>
@@ -53,7 +52,6 @@
     <maven-bundle-plugin.version>5.1.9</maven-bundle-plugin.version>
   </properties>
 
- 
 
   <dependencies>
     <dependency>
@@ -72,7 +70,7 @@
         <artifactId>reload4j</artifactId>
         <version>${reload4j.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>ch.qos.cal10n</groupId>
         <artifactId>cal10n-api</artifactId>
@@ -147,14 +145,14 @@
               <source>${jdk.version}</source>
               <target>${jdk.version}</target>
             </configuration>
-          </execution> 
+          </execution>
 
-          <execution>                      
+          <execution>
             <id>module-compile</id>
             <phase>compile</phase>
             <goals>
               <goal>compile</goal>
-            </goals>          
+            </goals>
             <configuration>
               <release>9</release>
               <compileSourceRoots>
@@ -165,7 +163,6 @@
           </execution>
 
 
-
         </executions>
 
       </plugin>
@@ -200,19 +197,19 @@
           <supportIncrementalBuild>true</supportIncrementalBuild>
           <!-- populated by the plugin itself -->
           <instructions>
-			  <Bundle-SymbolicName>${replacestring;${project.artifactId};-;.}</Bundle-SymbolicName>
-			  <Bundle-Vendor>SLF4J.ORG</Bundle-Vendor>
-			  <_snapshot/>
-			  <_exportcontents>!META-INF.versions.9,*;-noimport:=true</_exportcontents>
-			  <Bundle-Description>${project.description}</Bundle-Description>
-			  <Bundle-DocURL>${project.url}</Bundle-DocURL>
-			  <X-Compile-Source-JDK>${maven.compiler.source}</X-Compile-Source-JDK>
-			  <X-Compile-Target-JDK>${maven.compiler.target}</X-Compile-Target-JDK>
-			  <Implementation-Version>${project.version}</Implementation-Version>
-			  <Implementation-Title>${project.artifactId}</Implementation-Title>
-			  <Multi-Release>true</Multi-Release>
-			  <_removeheaders>Private-Package,Bundle-SCM, Bundle-Developers, Include-Resource</_removeheaders>
-		  </instructions>
+            <Bundle-SymbolicName>${replacestring;${project.artifactId};-;.}</Bundle-SymbolicName>
+            <Bundle-Vendor>SLF4J.ORG</Bundle-Vendor>
+            <_snapshot/>
+            <_exportcontents>!META-INF.versions.9,*;-noimport:=true</_exportcontents>
+            <Bundle-Description>${project.description}</Bundle-Description>
+            <Bundle-DocURL>${project.url}</Bundle-DocURL>
+            <X-Compile-Source-JDK>${maven.compiler.source}</X-Compile-Source-JDK>
+            <X-Compile-Target-JDK>${maven.compiler.target}</X-Compile-Target-JDK>
+            <Implementation-Version>${project.version}</Implementation-Version>
+            <Implementation-Title>${project.artifactId}</Implementation-Title>
+            <Multi-Release>true</Multi-Release>
+            <_removeheaders>Private-Package,Bundle-SCM, Bundle-Developers, Include-Resource</_removeheaders>
+          </instructions>
         </configuration>
         <executions>
           <execution>
@@ -267,71 +264,8 @@
         <version>3.0.0</version>
       </plugin>
     </plugins>
-  
-  </build>
 
-  <reporting>
-    <plugins>
-      <plugin>
-        <groupId>org.apache.maven.plugins</groupId>
-        <artifactId>maven-jxr-plugin</artifactId>
-        <version>${maven-jxr-plugin.version}</version>
-        <configuration>
-          <aggregate>true</aggregate>
-          <javadocDir>target/site/apidocs/</javadocDir>
-          <linkJavadoc>true</linkJavadoc>
-        </configuration>
-      </plugin>
-      
-      <plugin>
-        <groupId>org.apache.maven.plugins</groupId>
-        <artifactId>maven-javadoc-plugin</artifactId>
-        <version>${maven-javadoc-plugin.version}</version>
-        <configuration>
-          <linkJavadoc>true</linkJavadoc>
-          <linksource>true</linksource>
-          <aggregate>true</aggregate>
-          <additionalOptions>
-            <additionalOption>-Xdoclint:none</additionalOption>
-          </additionalOptions>
-          <excludePackageNames>org.slf4j.migrator:org.slf4j.migrator.*</excludePackageNames>
-          <sourceFileExcludes>
-            <sourceFileExclude>**/module-info.java</sourceFileExclude>
-          </sourceFileExcludes>
-          
-          <groups>
-            <group>
-              <title>SLF4J packages</title>
-              <packages>org.slf4j:org.slf4j.*</packages>
-            </group>
-            
-            <group>
-              <title>SLF4J extensions</title>
-              <packages>
-                org.slf4j.cal10n:org.slf4j.profiler:org.slf4j.ext:org.slf4j.instrumentation:org.slf4j.agent
-              </packages>
-            </group>
-            
-            <group>
-              <title>Jakarta Commons Logging packages</title>
-              <packages>org.apache.commons.*</packages>
-            </group>
-            
-            <group>
-              <title>java.util.logging (JUL) to SLF4J bridge</title>
-              <packages>org.slf4j.bridge</packages>
-            </group>
-            
-            <group>
-              <title>Apache log4j</title>
-              <packages>org.apache.log4j:org.apache.log4j.*</packages>
-            </group>
-          </groups>
-        </configuration>
-      </plugin>
-      
-    </plugins>
-  </reporting>
+  </build>
 
   <profiles>
     <profile>

pom.xml

@@ -6,28 +6,29 @@
 
   <groupId>org.slf4j</groupId>
   <artifactId>slf4j-bom</artifactId>
-  <version>2.0.10-SNAPSHOT</version>
+  <version>2.0.19-SNAPSHOT</version>
   <packaging>pom</packaging>
 
   <url>http://www.slf4j.org</url>
-  
+
   <name>SLF4J BOM</name>
   <description>SLF4J project BOM</description>
 
   <licenses>
     <license>
-      <name>MIT License</name>
-      <url>http://www.opensource.org/licenses/mit-license.php</url>
+      <name>MIT</name>
+      <url>https://opensource.org/license/mit</url>
       <distribution>repo</distribution>
     </license>
   </licenses>
 
+
   <scm>
     <url>https://github.com/qos-ch/slf4j</url>
     <connection>scm:git:https://github.com/qos-ch/slf4j.git</connection>
-  </scm>  
+  </scm>
+
 
-  
   <!-- Inspired by Improving the Maven Bill of Materials (BOM) Pattern  -->
   <!-- https://www.garretwilson.com/blog/2023/06/14/improve-maven-bom-pattern -->
   <modules>
@@ -38,7 +39,7 @@
     <module>slf4j-jdk14</module>
     <module>slf4j-jdk-platform-logging</module>
     <module>slf4j-log4j12</module>
-    <module>slf4j-reload4j</module>    
+    <module>slf4j-reload4j</module>
     <module>slf4j-ext</module>
     <module>jcl-over-slf4j</module>
     <module>log4j-over-slf4j</module>
@@ -48,6 +49,10 @@
     <module>slf4j-migrator</module>
   </modules>
 
+  <properties>
+      <central-publishing-maven-plugin.version>0.9.0</central-publishing-maven-plugin.version>
+  </properties>
+
   <dependencyManagement>
     <dependencies>
 
@@ -68,7 +73,7 @@
         <artifactId>slf4j-nop</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>org.slf4j</groupId>
         <artifactId>slf4j-jdk14</artifactId>
@@ -81,49 +86,49 @@
         <artifactId>slf4j-jdk-platform-logging</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>org.slf4j</groupId>
         <artifactId>slf4j-log4j12</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>org.slf4j</groupId>
         <artifactId>slf4j-reload4j</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>org.slf4j</groupId>
         <artifactId>slf4j-ext</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>org.slf4j</groupId>
         <artifactId>jcl-over-slf4j</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>org.slf4j</groupId>
         <artifactId>log4j-over-slf4j</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>org.slf4j</groupId>
         <artifactId>jul-to-slf4j</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
       <dependency>
         <groupId>org.slf4j</groupId>
         <artifactId>osgi-over-slf4j</artifactId>
         <version>${project.version}</version>
       </dependency>
-      
+
 
     </dependencies>
   </dependencyManagement>
@@ -145,8 +150,96 @@
     </developer>
   </developers>
 
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-javadoc-plugin</artifactId>
+        <version>3.6.3</version>
+        <configuration>
+          <verbose>true</verbose>
+          <skippedModules>
+             slf4j-jdk-platform-logging,slf4j-migrator,osgi-over-slf4j
+          </skippedModules>
+          <detectLinks>true</detectLinks>
+          <doctitle>SLF4J project modules ${project.version}</doctitle>
+          <windowtitle>SLF4J javadoc</windowtitle>
+          <bottom><![CDATA[Copyright  &copy; 2005-{currentYear} QOS.CH Sarl. All rights reserved]]></bottom>
+          <linksource>true</linksource>
+          <additionalOptions>
+            <additionalOption>-Xdoclint:none</additionalOption>
+          </additionalOptions>
+          <groups>
+            <group>
+              <title>SLF4J API packages</title>
+              <packages>org.slf4j:org.slf4j.spi:org.slf4j.event:org.slf4j.helpers</packages>
+            </group>
+
+            <group>
+              <title>slf4j-simple package</title>
+              <packages>org.slf4j.simple</packages>
+            </group>
+
+            <group>
+              <title>slf4j-nop package</title>
+              <packages>org.slf4j.nop</packages>
+            </group>
+
+
+            <group>
+              <title>slf4j-jdk14 package</title>
+              <packages>org.slf4j.jul</packages>
+            </group>
+
+
+            <group>
+              <title>slf4j-reload4j package</title>
+              <packages>org.slf4j.reload4j</packages>
+            </group>
+
+
+            <group>
+              <title>SLF4J extensions</title>
+              <packages>
+                org.slf4j.cal10n:org.slf4j.profiler:org.slf4j.ext:org.slf4j.instrumentation:org.slf4j.agent
+              </packages>
+            </group>
+
+            <group>
+              <title>Jakarta Commons Logging packages</title>
+              <packages>org.apache.commons.*</packages>
+            </group>
+
+            <group>
+              <title>java.util.logging (JUL) to SLF4J bridge</title>
+              <packages>org.slf4j.bridge</packages>
+            </group>
+
+            <group>
+              <title>log4j-over-slf4j redirection</title>
+              <packages>org.apache.log4j:org.apache.log4j.*</packages>
+            </group>
+          </groups>
+
+        </configuration>
+      </plugin>
+
+      <plugin>
+        <groupId>org.sonatype.central</groupId>
+        <artifactId>central-publishing-maven-plugin</artifactId>
+        <version>${central-publishing-maven-plugin.version}</version>
+        <extensions>true</extensions>
+        <configuration>
+          <publishingServerId>central</publishingServerId>
+          <excludeArtifacts>integration</excludeArtifacts>
+        </configuration>
+      </plugin>
+
+    </plugins>
+  </build>
+
   <profiles>
-    
+
     <profile>
       <id>sign-artifacts</id>
       <build>
@@ -169,5 +262,5 @@
       </build>
     </profile>
   </profiles>
-  
+
 </project>

release.sh

@@ -4,6 +4,10 @@
 #JDK8 - mvn site:site
 #rscpSLF4J apidocs/ 
 
+# JDK 11+
+# adding the following 
+#mvn -Ddoclint=none -Dadditionalparam=-Xdoclint:none  javadoc:aggregate
+
 
 #mvn versions:set -DgenerateBackupPoms=false -DnewVersion=${VERSION_NUMBER} 
 
@@ -42,8 +46,9 @@ echoRunAndCheck "$MVN install"
 
 if [ ! -z "$PASS"  ]
 then
-  export GPG_TTY=$(tty)    
-  echoRunAndCheck "$MVN deploy -P javadocjar,sign-artifacts"
+    # WARNING deploying without cleaning may leave stale MANIFEST files    
+    export GPG_TTY=$(tty)
+    echoRunAndCheck "$MVN deploy -P javadocjar,sign-artifacts"
 fi
 
 

slf4j-api/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

slf4j-api/src/main/java/org/slf4j/LoggerFactory.java

@@ -47,6 +47,7 @@ import org.slf4j.helpers.Reporter;
 import org.slf4j.helpers.SubstituteLogger;
 import org.slf4j.helpers.SubstituteServiceProvider;
 import org.slf4j.helpers.Util;
+import org.slf4j.spi.MDCAdapter;
 import org.slf4j.spi.SLF4JServiceProvider;
 
 /**
@@ -82,6 +83,9 @@ public final class LoggerFactory {
     static final String UNSUCCESSFUL_INIT_URL = CODES_PREFIX + "#unsuccessfulInit";
     static final String UNSUCCESSFUL_INIT_MSG = "org.slf4j.LoggerFactory in failed state. Original exception was thrown EARLIER. See also "
                     + UNSUCCESSFUL_INIT_URL;
+
+    static final String CONNECTED_WITH_MSG = "Connected with provider of type [";
+
     /**
      * System property for explicitly setting the provider class. If set and the provider could be instantiated,
      * then the service loading mechanism will be bypassed.
@@ -192,6 +196,7 @@ public final class LoggerFactory {
             reportMultipleBindingAmbiguity(providersList);
             if (providersList != null && !providersList.isEmpty()) {
                 PROVIDER = providersList.get(0);
+                earlyBindMDCAdapter();
                 // SLF4JServiceProvider.initialize() is intended to be called here and nowhere else.
                 PROVIDER.initialize();
                 INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
@@ -212,6 +217,19 @@ public final class LoggerFactory {
         }
     }
 
+    /**
+     * The value of PROVIDER.getMDCAdapter() can be null while PROVIDER has not yet initialized.
+     *
+     * However, SLF4JServiceProvider implementations are expected to initialize their internal
+     * MDCAdapter field in their constructor or on field declaration.
+     */
+    private static void earlyBindMDCAdapter() {
+        MDCAdapter mdcAdapter = PROVIDER.getMDCAdapter();
+        if(mdcAdapter != null) {
+            MDC.setMDCAdapter(mdcAdapter);
+        }
+    }
+
     static SLF4JServiceProvider loadExplicitlySpecified(ClassLoader classLoader) {
         String explicitlySpecified = System.getProperty(PROVIDER_PROPERTY_KEY);
         if (null == explicitlySpecified || explicitlySpecified.isEmpty()) {
@@ -403,9 +421,16 @@ public final class LoggerFactory {
     }
 
     private static void reportActualBinding(List<SLF4JServiceProvider> providerList) {
-        // binderPathSet can be null under Android
-        if (!providerList.isEmpty() && isAmbiguousProviderList(providerList)) {
+        // impossible since a provider has been found
+        if (providerList.isEmpty()) {
+            throw new IllegalStateException("No providers were found which is impossible after successful initialization.");
+        }
+
+        if (isAmbiguousProviderList(providerList)) {
             Reporter.info("Actual provider is of type [" + providerList.get(0) + "]");
+        } else {
+            SLF4JServiceProvider provider = providerList.get(0);
+            Reporter.debug(CONNECTED_WITH_MSG + provider.getClass().getName() + "]");
         }
     }
 

slf4j-api/src/main/java/org/slf4j/MDC.java

@@ -28,10 +28,7 @@ import java.io.Closeable;
 import java.util.Deque;
 import java.util.Map;
 
-import org.slf4j.helpers.BasicMDCAdapter;
-import org.slf4j.helpers.NOPMDCAdapter;
-import org.slf4j.helpers.Reporter;
-import org.slf4j.helpers.Util;
+import org.slf4j.helpers.*;
 import org.slf4j.spi.MDCAdapter;
 import org.slf4j.spi.SLF4JServiceProvider;
 
@@ -66,9 +63,9 @@ import org.slf4j.spi.SLF4JServiceProvider;
 public class MDC {
 
     static final String NULL_MDCA_URL = "http://www.slf4j.org/codes.html#null_MDCA";
-    private static final String MDC_APAPTER_CANNOT_BE_NULL_MESSAGE = "MDCAdapter cannot be null. See also " + NULL_MDCA_URL;
+    private static final String MDC_ADAPTER_CANNOT_BE_NULL_MESSAGE = "MDCAdapter cannot be null. See also " + NULL_MDCA_URL;
     static final String NO_STATIC_MDC_BINDER_URL = "http://www.slf4j.org/codes.html#no_static_mdc_binder";
-    static MDCAdapter mdcAdapter;
+    static MDCAdapter MDC_ADAPTER;
 
     /**
      * An adapter to remove the key when done.
@@ -88,14 +85,30 @@ public class MDC {
     private MDC() {
     }
 
-    static {
+    private static MDCAdapter getMDCAdapterGivenByProvider() {
         SLF4JServiceProvider provider = LoggerFactory.getProvider();
-        if (provider != null) {
-            mdcAdapter = provider.getMDCAdapter();
+        if(provider != null) {
+            // If you wish to change the mdc adapter, setting the MDC.MDCAdapter variable might be insufficient.
+            // Keep in mind that the provider *might* perform additional internal mdcAdapter assignments that
+            // you would also need to replicate/adapt.
+
+            // obtain and attach the MDCAdapter from the provider
+
+            final MDCAdapter anAdapter = provider.getMDCAdapter();
+            emitTemporaryMDCAdapterWarningIfNeeded(provider);
+            return anAdapter;
         } else {
             Reporter.error("Failed to find provider.");
             Reporter.error("Defaulting to no-operation MDCAdapter implementation.");
-            mdcAdapter = new NOPMDCAdapter();
+            return new NOPMDCAdapter();
+        }
+    }
+
+    private static void emitTemporaryMDCAdapterWarningIfNeeded(SLF4JServiceProvider provider) {
+        boolean isSubstitute = provider instanceof SubstituteServiceProvider;
+        if(isSubstitute) {
+            Reporter.info("Temporary mdcAdapter given by SubstituteServiceProvider.");
+            Reporter.info("This mdcAdapter will be replaced after backend initialization has completed.");
         }
     }
 
@@ -118,10 +131,10 @@ public class MDC {
         if (key == null) {
             throw new IllegalArgumentException("key parameter cannot be null");
         }
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
+        if (getMDCAdapter() == null) {
+            throw new IllegalStateException(MDC_ADAPTER_CANNOT_BE_NULL_MESSAGE);
         }
-        mdcAdapter.put(key, val);
+        getMDCAdapter().put(key, val);
     }
 
     /**
@@ -174,10 +187,8 @@ public class MDC {
             throw new IllegalArgumentException("key parameter cannot be null");
         }
 
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
-        }
-        return mdcAdapter.get(key);
+        mdcAdapterNullCheck();
+        return getMDCAdapter().get(key);
     }
 
     /**
@@ -195,20 +206,16 @@ public class MDC {
             throw new IllegalArgumentException("key parameter cannot be null");
         }
 
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
-        }
-        mdcAdapter.remove(key);
+        mdcAdapterNullCheck();
+        getMDCAdapter().remove(key);
     }
 
     /**
      * Clear all entries in the MDC of the underlying implementation.
      */
     public static void clear() {
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
-        }
-        mdcAdapter.clear();
+        mdcAdapterNullCheck();
+        getMDCAdapter().clear();
     }
 
     /**
@@ -219,10 +226,8 @@ public class MDC {
      * @since 1.5.1
      */
     public static Map<String, String> getCopyOfContextMap() {
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
-        }
-        return mdcAdapter.getCopyOfContextMap();
+        mdcAdapterNullCheck();
+        return getMDCAdapter().getCopyOfContextMap();
     }
 
     /**
@@ -237,23 +242,38 @@ public class MDC {
      * @since 1.5.1
      */
     public static void setContextMap(Map<String, String> contextMap) {
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
-        }
-        mdcAdapter.setContextMap(contextMap);
+        mdcAdapterNullCheck();
+        getMDCAdapter().setContextMap(contextMap);
     }
 
     /**
      * Returns the MDCAdapter instance currently in use.
-     * 
+     *
+     * Since 2.0.17, if the MDCAdapter instance is null, then this method set it to use
+     * the adapter returned by the SLF4JProvider. However, in the vast majority of cases
+     * the MDCAdapter will be set earlier (during initialization) by {@link LoggerFactory}.
+     *
      * @return the MDcAdapter instance currently in use.
      * @since 1.4.2
      */
     public static MDCAdapter getMDCAdapter() {
-        return mdcAdapter;
+        if(MDC_ADAPTER == null) {
+            MDC_ADAPTER = getMDCAdapterGivenByProvider();
+        }
+        return MDC_ADAPTER;
     }
 
-
+    /**
+     * Set MDCAdapter instance to use.
+     *
+     * @since 2.0.17
+     */
+    static void setMDCAdapter(MDCAdapter anMDCAdapter) {
+        if(anMDCAdapter == null) {
+            throw new IllegalStateException(MDC_ADAPTER_CANNOT_BE_NULL_MESSAGE);
+        }
+        MDC_ADAPTER = anMDCAdapter;
+    }
 
     /**
      * Push a value into the deque(stack) referenced by 'key'.
@@ -263,28 +283,24 @@ public class MDC {
      * @since 2.0.0
      */
     static public void pushByKey(String key, String value) {
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
-        }
-        mdcAdapter.pushByKey(key, value);
+        mdcAdapterNullCheck();
+        getMDCAdapter().pushByKey(key, value);
     }
     
     /**
-     * Pop the stack referenced by 'key' and return the value possibly null.
+     * Pop the <b>stack</b> referenced by 'key' and return the value possibly null.
      * 
      * @param key identifies the deque(stack)
      * @return the value just popped. May be null/
      * @since 2.0.0
      */
     static public String popByKey(String key) {
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
-        }
-        return mdcAdapter.popByKey(key);
+        mdcAdapterNullCheck();
+        return getMDCAdapter().popByKey(key);
     }
 
     /**
-     * Returns a copy of the deque(stack) referenced by 'key'. May be null.
+     * Returns a copy of the <b>deque(stack)</b> referenced by 'key'. May be null.
      * 
      * @param key identifies the  stack
      * @return copy of stack referenced by 'key'. May be null.
@@ -292,9 +308,13 @@ public class MDC {
      * @since 2.0.0
      */
     public Deque<String>  getCopyOfDequeByKey(String key) {
-        if (mdcAdapter == null) {
-            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
+        mdcAdapterNullCheck();
+        return getMDCAdapter().getCopyOfDequeByKey(key);
+    }
+
+    private static void mdcAdapterNullCheck() {
+        if (getMDCAdapter() == null) {
+            throw new IllegalStateException(MDC_ADAPTER_CANNOT_BE_NULL_MESSAGE);
         }
-        return mdcAdapter.getCopyOfDequeByKey(key);
     }
 }

slf4j-api/src/main/java/org/slf4j/event/LoggingEvent.java

@@ -23,6 +23,10 @@ public interface LoggingEvent {
 
     Object[] getArgumentArray();
 
+    /**
+     * List of markers in the event, might be null.
+     * @return markers in the event, might be null.
+     */
     List<Marker> getMarkers();
 
     List<KeyValuePair> getKeyValuePairs();

slf4j-api/src/main/java/org/slf4j/helpers/Reporter.java

@@ -3,11 +3,13 @@ package org.slf4j.helpers;
 import java.io.PrintStream;
 
 /**
- * An internally used class for reporting internal messages generated by SLF4J itself during initialization.
+ * An internally used class for reporting internal messages generated by SLF4J itself, typically
+ * during initialization.
  *
  * <p>
- * Internal reporting is performed by calling the {@link #info(String)}, {@link #warn(String)} (String)}
- * {@link #error(String)} (String)}  and {@link  #error(String, Throwable)} methods.
+ * Internal reporting is performed by calling the {@link #debug(String)}, {@link #info(String)},
+ * {@link #warn(String)} (String)} {@link #error(String)} (String)}  and
+ * {@link  #error(String, Throwable)} methods.
  * </p>
  * <p>See {@link #SLF4J_INTERNAL_VERBOSITY_KEY} and {@link #SLF4J_INTERNAL_REPORT_STREAM_KEY} for
  * configuration options.</p>
@@ -23,7 +25,7 @@ public class Reporter {
      * this class is used internally by Reporter
      */
     private enum Level {
-        INFO(1), WARN(2), ERROR(3);
+        DEBUG(0), INFO(1), WARN(2), ERROR(3);
 
         int levelInt;
 
@@ -40,6 +42,7 @@ public class Reporter {
         Stderr, Stdout;
     }
 
+    static final String SLF4J_DEBUG_PREFIX = "SLF4J(D): ";
     static final String SLF4J_INFO_PREFIX = "SLF4J(I): ";
     static final String SLF4J_WARN_PREFIX = "SLF4J(W): ";
     static final String SLF4J_ERROR_PREFIX = "SLF4J(E): ";
@@ -62,11 +65,11 @@ public class Reporter {
     public static final String SLF4J_INTERNAL_VERBOSITY_KEY = "slf4j.internal.verbosity";
 
 
-    static private final TargetChoice TARGET_CHOICE = initTargetChoice();
+    static private final TargetChoice TARGET_CHOICE = getTargetChoice();
 
     static private final Level INTERNAL_VERBOSITY = initVerbosity();
 
-    static private TargetChoice initTargetChoice() {
+    static private TargetChoice getTargetChoice() {
         String reportStreamStr = System.getProperty(SLF4J_INTERNAL_REPORT_STREAM_KEY);
 
         if(reportStreamStr == null || reportStreamStr.isEmpty()) {
@@ -88,6 +91,10 @@ public class Reporter {
             return Level.INFO;
         }
 
+        if(verbosityStr.equalsIgnoreCase("DEBUG")) {
+            return Level.DEBUG;
+        }
+
         if(verbosityStr.equalsIgnoreCase("ERROR")) {
             return Level.ERROR;
         }
@@ -97,6 +104,7 @@ public class Reporter {
             return Level.WARN;
         }
 
+        // anything else including verbosityStr.equalsIgnoreCase("INFO")
         return Level.INFO;
     }
 
@@ -114,13 +122,30 @@ public class Reporter {
         }
     }
 
+    /**
+     * Report an internal message of level DEBUG. Message text is prefixed with the string "SLF4J(D)",
+     * with (D) standing as a shorthand for DEBUG.
+     *
+     * <p>Messages of level DEBUG are be enabled when the {@link #SLF4J_INTERNAL_VERBOSITY_KEY}
+     * system property is set to "DEBUG" and disabled when set to "INFO", "WARN" or "ERROR". By default,
+     * {@link #SLF4J_INTERNAL_VERBOSITY_KEY} is set to "INFO".</p>
+     *
+     * @param msg the message text
+     * @since 2.0.16
+     */
+    public static void debug(String msg) {
+        if(isEnabledFor(Level.DEBUG)) {
+            getTarget().println(SLF4J_DEBUG_PREFIX + msg);
+        }
+    }
+
     /**
      * Report an internal message of level INFO. Message text is prefixed with the string "SLF4J(I)", with
      * (I) standing as a shorthand for INFO.
      *
      * <p>Messages of level INFO are be enabled when the {@link #SLF4J_INTERNAL_VERBOSITY_KEY} system property is
-     * set to "INFO" and disabled when set to "WARN" or "ERROR". By default, {@link #SLF4J_INTERNAL_VERBOSITY_KEY} is
-     * set to "INFO".</p>
+     * set to "DEBUG" or "INFO" and disabled when set to "WARN" or "ERROR". By default,
+     * {@link #SLF4J_INTERNAL_VERBOSITY_KEY} is set to "INFO".</p>
      *
      * @param msg the message text
      */
@@ -136,8 +161,8 @@ public class Reporter {
      * (W) standing as a shorthand for  WARN.
      *
      * <p>Messages of level WARN are be enabled when the {@link #SLF4J_INTERNAL_VERBOSITY_KEY} system property is
-     * set to "INFO" or "WARN" and disabled when set to "ERROR". By default, {@link #SLF4J_INTERNAL_VERBOSITY_KEY} is
-     * set to "INFO".</p>
+     * set to "DEBUG", "INFO" or "WARN" and disabled when set to "ERROR". By default,
+     * {@link #SLF4J_INTERNAL_VERBOSITY_KEY} is set to "INFO".</p>
      *
      * @param msg the message text
      */
@@ -147,7 +172,6 @@ public class Reporter {
         }
     }
 
-
     /**
      * Report an internal message of level "ERROR  accompanied by a {@link Throwable}.
      * Message text is prefixed with the string "SLF4J(E)", with (E) standing as a shorthand for ERROR.
@@ -164,10 +188,9 @@ public class Reporter {
         t.printStackTrace(getTarget());
     }
 
-
     /**
-     * Report an internal message of level "ERROR". Message text is prefixed with the string "SLF4J(E)", with
-     * (E)  standing as a shorthand for ERROR.
+     * Report an internal message of level "ERROR". Message text is prefixed with the string "SLF4J(E)",
+     * with (E)  standing as a shorthand for ERROR.
      *
      * <p>Messages of level ERROR are always enabled.
      *

slf4j-api/src/main/java/org/slf4j/helpers/Slf4jEnvUtil.java

@@ -0,0 +1,73 @@
+/*
+ *  Copyright (c) 2004-2024 QOS.ch
+ *  All rights reserved.
+ *
+ *  Permission is hereby granted, free  of charge, to any person obtaining
+ *  a  copy  of this  software  and  associated  documentation files  (the
+ *  "Software"), to  deal in  the Software without  restriction, including
+ *  without limitation  the rights to  use, copy, modify,  merge, publish,
+ *  distribute,  sublicense, and/or sell  copies of  the Software,  and to
+ *  permit persons to whom the Software  is furnished to do so, subject to
+ *  the following conditions:
+ *
+ *  The  above  copyright  notice  and  this permission  notice  shall  be
+ *  included in all copies or substantial portions of the Software.
+ *
+ *  THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
+ *  EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
+ *  MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
+ *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ *  OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
+ *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package org.slf4j.helpers;
+
+/**
+ * Various utility methods
+ *
+ * @since 2.0.14
+ */
+public class Slf4jEnvUtil {
+
+
+    /**
+     * Returns the current version of slf4j, or null if data is not available.
+     *
+     * @return current version or null if missing version data
+     * @since 2.0.14
+     */
+    static public String slf4jVersion() {
+//        String moduleVersion = slf4jVersionByModule();
+//        if(moduleVersion != null)
+//            return moduleVersion;
+
+        Package pkg = Slf4jEnvUtil.class.getPackage();
+        if(pkg == null) {
+            return null;
+        }
+        final String pkgVersion = pkg.getImplementationVersion();
+        return pkgVersion;
+    }
+
+    /**
+     * Returns the current version of slf4j via class.getModule()
+     * or null if data is not available.
+     *
+     * @return current version or null if missing version data
+     * @since 2.0.14
+     */
+//    static private String slf4jVersionByModule() {
+//        Module module = Slf4jEnvUtil.class.getModule();
+//        if (module == null)
+//            return null;
+//
+//        ModuleDescriptor md = module.getDescriptor();
+//        if (md == null)
+//            return null;
+//        Optional<String> opt = md.rawVersion();
+//        return opt.orElse(null);
+//    }
+
+}

slf4j-api/src/main/java/org/slf4j/helpers/SubstituteServiceProvider.java

@@ -7,8 +7,18 @@ import org.slf4j.spi.SLF4JServiceProvider;
 
 public class SubstituteServiceProvider implements SLF4JServiceProvider {
     private final SubstituteLoggerFactory loggerFactory = new SubstituteLoggerFactory();
-    private final IMarkerFactory markerFactory = new BasicMarkerFactory();
-    private final MDCAdapter mdcAdapter = new BasicMDCAdapter();
+
+    // LoggerFactory expects providers to initialize markerFactory as early as possible.
+    private final IMarkerFactory markerFactory;
+
+    // LoggerFactory expects providers to initialize their MDCAdapter field
+    // as early as possible, preferably at construction time.
+    private final MDCAdapter mdcAdapter;
+
+    public SubstituteServiceProvider() {
+        markerFactory = new BasicMarkerFactory();
+        mdcAdapter = new BasicMDCAdapter();
+    }
 
     @Override
     public ILoggerFactory getLoggerFactory() {
@@ -36,6 +46,5 @@ public class SubstituteServiceProvider implements SLF4JServiceProvider {
 
     @Override
     public void initialize() {
-
     }
 }

slf4j-api/src/main/java/org/slf4j/helpers/Util.java

@@ -117,14 +117,28 @@ public final class Util {
         return trace[i + 2];
     }
 
-//    private static final void report(String msg, Throwable t) {
-//        System.err.println(msg);
-//        System.err.println("Reported exception:");
-//        t.printStackTrace();
-//    }
-//
-//    static final private void report(String msg) {
-//        System.err.println("SLF4J: " + msg);
-//    }
+    /**
+     * See  {@link Reporter#error(String, Throwable)} class for alternative.
+     *
+     * @deprecated replaced by the {@link Reporter#error(String, Throwable)} method.
+     * @param msg message to print
+     * @param t throwable to print
+     */
+    static final public void report(String msg, Throwable t) {
+        System.err.println(msg);
+        System.err.println("Reported exception:");
+        t.printStackTrace();
+    }
+
+    /**
+     * See  {@link Reporter} class for alternatives.
+     *
+     * @deprecated replaced by one of {@link Reporter#info(String)},
+     * {@link Reporter#warn(String)} or {@link Reporter#error(String)} methods.
+     * @param msg message to print
+     */
+    static final public void report(String msg) {
+        System.err.println("SLF4J: " + msg);
+    }
 
 }

slf4j-api/src/main/java/org/slf4j/spi/DefaultLoggingEventBuilder.java

@@ -1,7 +1,7 @@
 /**
  * Copyright (c) 2004-2022 QOS.ch
  * All rights reserved.
- *
+ * <p>
  * Permission is hereby granted, free  of charge, to any person obtaining
  * a  copy  of this  software  and  associated  documentation files  (the
  * "Software"), to  deal in  the Software without  restriction, including
@@ -9,10 +9,10 @@
  * distribute,  sublicense, and/or sell  copies of  the Software,  and to
  * permit persons to whom the Software  is furnished to do so, subject to
  * the following conditions:
- *
+ * <p>
  * The  above  copyright  notice  and  this permission  notice  shall  be
  * included in all copies or substantial portions of the Software.
- *
+ * <p>
  * THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
  * EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
  * MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
@@ -20,10 +20,10 @@
  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  * OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- *
  */
 package org.slf4j.spi;
 
+import java.util.List;
 import java.util.function.Supplier;
 
 import org.slf4j.Logger;
@@ -38,11 +38,11 @@ import org.slf4j.event.LoggingEvent;
  */
 public class DefaultLoggingEventBuilder implements LoggingEventBuilder, CallerBoundaryAware {
 
-    
+
     // The caller boundary when the log() methods are invoked, is this class itself.
-    
+
     static String DLEB_FQCN = DefaultLoggingEventBuilder.class.getName();
-    
+
     protected DefaultLoggingEvent loggingEvent;
     protected Logger logger;
 
@@ -53,7 +53,7 @@ public class DefaultLoggingEventBuilder implements LoggingEventBuilder, CallerBo
 
     /**
      * Add a marker to the current logging event being built.
-     * 
+     * <p>
      * It is possible to add multiple markers to the same logging event.
      *
      * @param marker the marker to add
@@ -72,165 +72,16 @@ public class DefaultLoggingEventBuilder implements LoggingEventBuilder, CallerBo
 
     @Override
     public LoggingEventBuilder addArgument(Object p) {
-        loggingEvent.addArgument(p);
+        this.loggingEvent.addArgument(p);
         return this;
     }
 
     @Override
     public LoggingEventBuilder addArgument(Supplier<?> objectSupplier) {
-        loggingEvent.addArgument(objectSupplier.get());
+        this.loggingEvent.addArgument(objectSupplier.get());
         return this;
     }
 
-    @Override
-    public void setCallerBoundary(String fqcn) {
-        loggingEvent.setCallerBoundary(fqcn);
-    }
-
-    @Override
-    public void log() {
-        log(loggingEvent);
-    }
-
-    @Override
-    public LoggingEventBuilder setMessage(String message) {
-        loggingEvent.setMessage(message);
-        return this;
-    }
-    @Override
-    public LoggingEventBuilder setMessage(Supplier<String> messageSupplier) {
-        loggingEvent.setMessage(messageSupplier.get());
-        return this;
-    }
-
-    @Override
-    public void log(String message) {
-        loggingEvent.setMessage(message);
-        log(loggingEvent);
-    }
-
-    @Override
-    public void log(String message, Object arg) {
-        loggingEvent.setMessage(message);
-        loggingEvent.addArgument(arg);
-        log(loggingEvent);
-    }
-
-    @Override
-    public void log(String message, Object arg0, Object arg1) {
-        loggingEvent.setMessage(message);
-        loggingEvent.addArgument(arg0);
-        loggingEvent.addArgument(arg1);
-        log(loggingEvent);
-    }
-
-    @Override
-    public void log(String message, Object... args) {
-        loggingEvent.setMessage(message);
-        loggingEvent.addArguments(args);
-
-        log(loggingEvent);
-    }
-
-    @Override
-    public void log(Supplier<String> messageSupplier) {
-        if (messageSupplier == null) {
-            log((String) null);
-        } else {
-            log(messageSupplier.get());
-        }
-    }
-    
-    protected void log(LoggingEvent aLoggingEvent) {
-        setCallerBoundary(DLEB_FQCN);
-        if (logger instanceof LoggingEventAware) {
-            ((LoggingEventAware) logger).log(aLoggingEvent);
-        } else {
-            logViaPublicSLF4JLoggerAPI(aLoggingEvent);
-        }
-    }
-
-    private void logViaPublicSLF4JLoggerAPI(LoggingEvent aLoggingEvent) {
-        Object[] argArray = aLoggingEvent.getArgumentArray();
-        int argLen = argArray == null ? 0 : argArray.length;
-
-        Throwable t = aLoggingEvent.getThrowable();
-        int tLen = t == null ? 0 : 1;
-
-        String msg = aLoggingEvent.getMessage();
-
-        Object[] combinedArguments = new Object[argLen + tLen];
-
-        if (argArray != null) {
-            System.arraycopy(argArray, 0, combinedArguments, 0, argLen);
-        }
-        if (t != null) {
-            combinedArguments[argLen] = t;
-        }
-
-        msg = mergeMarkersAndKeyValuePairs(aLoggingEvent, msg);
-
-        switch (aLoggingEvent.getLevel()) {
-        case TRACE:
-            logger.trace(msg, combinedArguments);
-            break;
-        case DEBUG:
-            logger.debug(msg, combinedArguments);
-            break;
-        case INFO:
-            logger.info(msg, combinedArguments);
-            break;
-        case WARN:
-            logger.warn(msg, combinedArguments);
-            break;
-        case ERROR:
-            logger.error(msg, combinedArguments);
-            break;
-        }
-
-    }
-
-    /**
-     * Prepend markers and key-value pairs to the message.
-     * 
-     * @param aLoggingEvent
-     * @param msg
-     * @return
-     */
-    private String mergeMarkersAndKeyValuePairs(LoggingEvent aLoggingEvent, String msg) {
-
-        StringBuilder sb = null;
-
-        if (aLoggingEvent.getMarkers() != null) {
-            sb = new StringBuilder();
-            for (Marker marker : aLoggingEvent.getMarkers()) {
-                sb.append(marker);
-                sb.append(' ');
-            }
-        }
-
-        if (aLoggingEvent.getKeyValuePairs() != null) {
-            if (sb == null) {
-                sb = new StringBuilder();
-            }
-            for (KeyValuePair kvp : aLoggingEvent.getKeyValuePairs()) {
-                sb.append(kvp.key);
-                sb.append('=');
-                sb.append(kvp.value);
-                sb.append(' ');
-            }
-        }
-
-        if (sb != null) {
-            sb.append(msg);
-            return sb.toString();
-        } else {
-            return msg;
-        }
-    }
-
-
-
     @Override
     public LoggingEventBuilder addKeyValue(String key, Object value) {
         loggingEvent.addKeyValue(key, value);
@@ -243,4 +94,184 @@ public class DefaultLoggingEventBuilder implements LoggingEventBuilder, CallerBo
         return this;
     }
 
+    @Override
+    public void setCallerBoundary(String fqcn) {
+        this.loggingEvent.setCallerBoundary(fqcn);
+    }
+
+    @Override
+    public void log() {
+        log(this.loggingEvent);
+    }
+
+    @Override
+    public LoggingEventBuilder setMessage(String message) {
+        this.loggingEvent.setMessage(message);
+        return this;
+    }
+
+    @Override
+    public LoggingEventBuilder setMessage(Supplier<String> messageSupplier) {
+        this.loggingEvent.setMessage(messageSupplier.get());
+        return this;
+    }
+
+    @Override
+    public void log(String message) {
+        this.loggingEvent.setMessage(message);
+        log(this.loggingEvent);
+    }
+
+    @Override
+    public void log(String message, Object arg) {
+        this.loggingEvent.setMessage(message);
+        this.loggingEvent.addArgument(arg);
+        log(this.loggingEvent);
+    }
+
+    @Override
+    public void log(String message, Object arg0, Object arg1) {
+        this.loggingEvent.setMessage(message);
+        this.loggingEvent.addArgument(arg0);
+        this.loggingEvent.addArgument(arg1);
+        log(this.loggingEvent);
+    }
+
+    @Override
+    public void log(String message, Object... args) {
+        this.loggingEvent.setMessage(message);
+        this.loggingEvent.addArguments(args);
+
+        log(this.loggingEvent);
+    }
+
+    @Override
+    public void log(Supplier<String> messageSupplier) {
+        if(messageSupplier == null) {
+            log((String) null);
+        } else {
+            log(messageSupplier.get());
+        }
+    }
+
+    protected void log(LoggingEvent aLoggingEvent) {
+        if(aLoggingEvent.getCallerBoundary() == null) {
+            setCallerBoundary(DLEB_FQCN);
+        }
+
+        if(logger instanceof LoggingEventAware) {
+            ((LoggingEventAware) logger).log(aLoggingEvent);
+        } else if(logger instanceof LocationAwareLogger) {
+            logViaLocationAwareLoggerAPI((LocationAwareLogger) logger, aLoggingEvent);
+        } else {
+            logViaPublicSLF4JLoggerAPI(aLoggingEvent);
+        }
+    }
+
+    private void logViaLocationAwareLoggerAPI(LocationAwareLogger locationAwareLogger, LoggingEvent aLoggingEvent) {
+        List<Marker> markerList = aLoggingEvent.getMarkers();
+        Marker firstMarker = (markerList != null && !markerList.isEmpty()) ? markerList.get(0) : null;
+        String mergedMessage = mergeMarkersAndKeyValuePairsAndMessage(aLoggingEvent);
+        locationAwareLogger.log(firstMarker, aLoggingEvent.getCallerBoundary(), aLoggingEvent.getLevel().toInt(),
+                                mergedMessage,
+                                aLoggingEvent.getArgumentArray(), aLoggingEvent.getThrowable());
+    }
+
+    private void logViaPublicSLF4JLoggerAPI(LoggingEvent aLoggingEvent) {
+        Object[] argArray = aLoggingEvent.getArgumentArray();
+        int argLen = argArray == null ? 0 : argArray.length;
+
+        Throwable t = aLoggingEvent.getThrowable();
+        int tLen = t == null ? 0 : 1;
+
+        Object[] combinedArguments = new Object[argLen + tLen];
+
+        if(argArray != null) {
+            System.arraycopy(argArray, 0, combinedArguments, 0, argLen);
+        }
+        if(t != null) {
+            combinedArguments[argLen] = t;
+        }
+
+        String mergedMessage = mergeMarkersAndKeyValuePairsAndMessage(aLoggingEvent);
+
+
+        switch(aLoggingEvent.getLevel()) {
+            case TRACE:
+                logger.trace(mergedMessage, combinedArguments);
+                break;
+            case DEBUG:
+                logger.debug(mergedMessage, combinedArguments);
+                break;
+            case INFO:
+                logger.info(mergedMessage, combinedArguments);
+                break;
+            case WARN:
+                logger.warn(mergedMessage, combinedArguments);
+                break;
+            case ERROR:
+                logger.error(mergedMessage, combinedArguments);
+                break;
+        }
+    }
+
+
+    /**
+     * Prepend markers and key-value pairs to the message.
+     *
+     * @param aLoggingEvent
+     *
+     * @return
+     */
+    private String mergeMarkersAndKeyValuePairsAndMessage(LoggingEvent aLoggingEvent) {
+        StringBuilder sb = mergeMarkers(aLoggingEvent.getMarkers(), null);
+        sb = mergeKeyValuePairs(aLoggingEvent.getKeyValuePairs(), sb);
+        final String mergedMessage = mergeMessage(aLoggingEvent.getMessage(), sb);
+        return mergedMessage;
+    }
+
+    private StringBuilder mergeMarkers(List<Marker> markerList, StringBuilder sb) {
+        if(markerList == null || markerList.isEmpty())
+            return sb;
+
+        if(sb == null)
+            sb = new StringBuilder();
+
+        for(Marker marker : markerList) {
+            sb.append(marker);
+            sb.append(' ');
+        }
+        return sb;
+    }
+
+    private StringBuilder mergeKeyValuePairs(List<KeyValuePair> keyValuePairList, StringBuilder sb) {
+        if(keyValuePairList == null || keyValuePairList.isEmpty())
+            return sb;
+
+        if(sb == null)
+            sb = new StringBuilder();
+
+        for(KeyValuePair kvp : keyValuePairList) {
+            sb.append(kvp.key);
+            sb.append('=');
+            sb.append(kvp.value);
+            sb.append(' ');
+        }
+        return sb;
+    }
+
+    private String mergeMessage(String msg, StringBuilder sb) {
+        if(sb != null) {
+            sb.append(msg);
+            return sb.toString();
+        } else {
+            return msg;
+        }
+    }
+
+
+
+
+
+
 }

slf4j-api/src/main/java/org/slf4j/spi/MDCAdapter.java

@@ -93,7 +93,7 @@ public interface MDCAdapter {
     public void setContextMap(Map<String, String> contextMap);
     
     /**
-     * Push a value into the deque(stack) referenced by 'key'.
+     * Push a value into the <b>deque(stack)</b> referenced by 'key'.
      *      
      * @param key identifies the appropriate stack
      * @param value the value to push into the stack
@@ -102,7 +102,7 @@ public interface MDCAdapter {
     public void pushByKey(String key, String value);
     
     /**
-     * Pop the stack referenced by 'key' and return the value possibly null.
+     * Pop the <b>stack</b> referenced by 'key' and return the value possibly null.
      * 
      * @param key identifies the deque(stack)
      * @return the value just popped. May be null/
@@ -111,7 +111,7 @@ public interface MDCAdapter {
     public String popByKey(String key);
 
     /**
-     * Returns a copy of the deque(stack) referenced by 'key'. May be null.
+     * Returns a copy of the <b>deque(stack)</b> referenced by 'key'. May be null.
      * 
      * @param key identifies the  stack
      * @return copy of stack referenced by 'key'. May be null.
@@ -122,7 +122,7 @@ public interface MDCAdapter {
     
 
     /**
-     * Clear the deque(stack) referenced by 'key'. 
+     * Clear the <b>deque(stack)</b> referenced by 'key'.
      * 
      * @param key identifies the  stack
      * 

slf4j-api/src/test/java/org/slf4j/basicTests/NoBindingTest.java

@@ -29,6 +29,8 @@ import static org.junit.Assert.assertTrue;
 
 import java.util.Random;
 
+import org.junit.After;
+import org.junit.Before;
 import org.junit.Test;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -37,11 +39,21 @@ import org.slf4j.Marker;
 import org.slf4j.MarkerFactory;
 import org.slf4j.helpers.BasicMarker;
 import org.slf4j.helpers.NOPLogger;
+import org.slf4j.helpers.Reporter;
 
 public class NoBindingTest {
 
     int diff = new Random().nextInt(10000);
 
+    @Before
+    public void setUp() throws Exception {
+        System.setProperty(Reporter.SLF4J_INTERNAL_VERBOSITY_KEY, "debug");
+    }
+    @After
+    public void tearDown() throws Exception {
+        System.clearProperty(Reporter.SLF4J_INTERNAL_VERBOSITY_KEY);
+    }
+
     @Test
     public void testLogger() {
         Logger logger = LoggerFactory.getLogger(NoBindingTest.class);

slf4j-api/src/test/java/org/slf4j/testHarness/MultithreadedInitializationTest.java

@@ -36,16 +36,15 @@ abstract public class MultithreadedInitializationTest {
 
         assertAllSubstLoggersAreFixed();
         long recordedEventCount = getRecordedEventCount();
-        int LENIENCY_COUNT = 21;
+        int LENIENCY_COUNT = 30;
 
         long expectedEventCount = eventCount.get() + extraLogEvents();
 
-        assertTrue(expectedEventCount + " >= " + recordedEventCount, expectedEventCount >= recordedEventCount);
-        assertTrue(expectedEventCount + " < " + recordedEventCount + "+" + LENIENCY_COUNT, expectedEventCount < recordedEventCount + LENIENCY_COUNT);
-    }
+        assertTrue("unmet condition: " + expectedEventCount + " >= " + recordedEventCount, expectedEventCount >= recordedEventCount);
+        assertTrue("unmet condition: " + expectedEventCount + " < " + recordedEventCount + "+" + LENIENCY_COUNT, expectedEventCount < (recordedEventCount + LENIENCY_COUNT));   }
 
     abstract protected long getRecordedEventCount();
-
+    
     protected int extraLogEvents() {
         return 0;
     }

slf4j-ext/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

slf4j-jdk-platform-logging/pom.xml

@@ -8,7 +8,7 @@
   <parent>
     <artifactId>slf4j-parent</artifactId>
     <groupId>org.slf4j</groupId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

slf4j-jdk-platform-logging/src/main/java/org/slf4j/jdk/platform/logging/SLF4JPlatformLogger.java

@@ -115,16 +115,11 @@ class SLF4JPlatformLogger implements System.Logger {
      * @param thrown
      * @param params
      */
-    private void log(Level jplLevel, ResourceBundle bundle, String msg, Throwable thrown, Object... params) {
-        if (jplLevel == Level.OFF)
-            return;
+    private void log(final Level jplLevel, final ResourceBundle bundle, final String msg, final Throwable thrown, final Object... params) {
 
-        if (jplLevel == Level.ALL) {
-            performLog(org.slf4j.event.Level.TRACE, bundle, msg, thrown, params);
-            return;
-        }
+        final Level jplLevelReduced = fixExtremeLevels(jplLevel);
 
-        org.slf4j.event.Level slf4jLevel = jplLevelToSLF4JLevel(jplLevel);
+        org.slf4j.event.Level slf4jLevel = jplLevelToSLF4JLevel(jplLevelReduced);
         boolean isEnabled = slf4jLogger.isEnabledForLevel(slf4jLevel);
 
         if (isEnabled) {
@@ -132,6 +127,27 @@ class SLF4JPlatformLogger implements System.Logger {
         }
     }
 
+    /**
+     * <p>Level.OFF and Level.ALL levels are not supposed to be used when calling log printing methods.
+     * </p>
+     *
+     * <p>We compensate for such incorrect usage by transforming Level.OFF as Level.ERROR and
+     * Level.ALL as Level.TRACE.
+     * </p>
+     *
+     * @param jplLevel
+     * @return
+     */
+    private Level fixExtremeLevels(Level jplLevel) {
+        if (jplLevel == Level.OFF)
+            return  Level.ERROR;
+
+        if (jplLevel == Level.ALL)
+            return Level.TRACE;
+
+        return jplLevel;
+    }
+
     private void performLog(org.slf4j.event.Level slf4jLevel, ResourceBundle bundle, String msg, Throwable thrown, Object... params) {
         String message = getResourceStringOrMessage(bundle, msg);
         LoggingEventBuilder leb = slf4jLogger.makeLoggingEventBuilder(slf4jLevel);

slf4j-jdk-platform-logging/src/test/java/org/slf4j/jdk/platform/logging/test/SLF4JPlatformLoggingTest.java

@@ -39,6 +39,7 @@ import org.junit.After;
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Test;
+import org.slf4j.LoggerFactory;
 
 /**
  * The present test is fragile in the sense that it sets up SimpleLogger
@@ -108,12 +109,27 @@ public class SLF4JPlatformLoggingTest {
         //INFO throwTest - a problem
         //java.lang.Exception
         //        at org.slf4j.jdk.platform.logging/org.slf4j.jdk.platform.logging.SLF4JPlatformLoggingTest.throwTest(SLF4JPlatformLoggingTest.java:92)
-         
-        assertEquals("INFO throwTest - we have a problem", results.get(0));
-        assertEquals(Exception.class.getName(), results.get(1));
-        assertTrue(results.get(2).contains("at "));
-        assertTrue(results.get(2).contains(this.getClass().getName()));
+
+        int line = 0;
+        //assertTrue(results.get(0).startsWith("SLF4J(I): Connected with provider of type ["));
+        assertEquals("INFO throwTest - we have a problem", results.get(line++));
+        assertEquals(Exception.class.getName(), results.get(line++));
+        assertTrue(results.get(line).contains("at "));
+        assertTrue(results.get(line++).contains(this.getClass().getName()));
     }
 
+    @Test
+    public void extremeLevels() throws IOException {
+        LoggerFinder finder = System.LoggerFinder.getLoggerFinder();
+        assertEquals(EXPECTED_FINDER_CLASS, finder.getClass().getName());
+        Logger systemLogger = finder.getLogger("extremeLevels", null);
+        systemLogger.log(Level.OFF, "hello");
+        systemLogger.log(Level.ALL, "world");
+
+        List<String> results = SPS.stringList;
+        assertEquals(1, results.size());
+        assertEquals("ERROR extremeLevels - hello", results.get(0));
+
+    }
 
 }

slf4j-jdk14/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

slf4j-jdk14/src/main/java/org/slf4j/jul/JDK14LoggerAdapter.java

@@ -55,6 +55,8 @@ public final class JDK14LoggerAdapter extends LegacyAbstractLogger implements Lo
 
     transient final java.util.logging.Logger logger;
 
+    static int NOT_FOUND = -1;
+
     // WARN: JDK14LoggerAdapter constructor should have only package access so
     // that only JDK14LoggerFactory be able to create one.
     JDK14LoggerAdapter(java.util.logging.Logger logger) {
@@ -181,26 +183,10 @@ public final class JDK14LoggerAdapter extends LegacyAbstractLogger implements Lo
     final private void fillCallerData(String callerFQCN, LogRecord record) {
         StackTraceElement[] steArray = new Throwable().getStackTrace();
 
-        int selfIndex = -1;
-        for (int i = 0; i < steArray.length; i++) {
-            final String className = steArray[i].getClassName();
+        int furthestIndex = findFurthestIndex(callerFQCN, steArray);
 
-            if (barrierMatch(callerFQCN, className)) {
-                selfIndex = i;
-                break;
-            }
-        }
-
-        int found = -1;
-        for (int i = selfIndex + 1; i < steArray.length; i++) {
-            final String className = steArray[i].getClassName();
-            if (!(barrierMatch(callerFQCN, className))) {
-                found = i;
-                break;
-            }
-        }
-
-        if (found != -1) {
+        if (furthestIndex != NOT_FOUND) {
+            int found = furthestIndex+1;
             StackTraceElement ste = steArray[found];
             // setting the class name has the side effect of setting
             // the needToInferCaller variable to false.
@@ -209,7 +195,24 @@ public final class JDK14LoggerAdapter extends LegacyAbstractLogger implements Lo
         }
     }
 
-    static String SELF = JDK14LoggerAdapter.class.getName();
+    // find the furthest index which matches any of the barrier classes
+    // We assume that the actual caller is at most MAX_SEARCH_DEPTH calls away
+    private int findFurthestIndex(String callerFQCN, StackTraceElement[] steArray) {
+
+        final int maxIndex = Math.min(MAX_SEARCH_DEPTH, steArray.length);
+        int furthestIndex = NOT_FOUND;
+
+        for (int i = 0; i < maxIndex; i++) {
+            final String className = steArray[i].getClassName();
+            if (barrierMatch(callerFQCN, className)) {
+                furthestIndex = i;
+            }
+        }
+        return furthestIndex;
+    }
+
+   static final int MAX_SEARCH_DEPTH = 12;
+   static String SELF = JDK14LoggerAdapter.class.getName();
 
     static String SUPER = LegacyAbstractLogger.class.getName();
     static String SUPER_OF_SUPER = AbstractLogger.class.getName();

slf4j-jdk14/src/main/java/org/slf4j/jul/JULServiceProvider.java

@@ -17,8 +17,16 @@ public class JULServiceProvider implements SLF4JServiceProvider {
     public static String REQUESTED_API_VERSION = "2.0.99"; // !final
 
     private ILoggerFactory loggerFactory;
-    private IMarkerFactory markerFactory;
-    private MDCAdapter mdcAdapter;
+    // LoggerFactory expects providers to initialize markerFactory as early as possible.
+    private final IMarkerFactory markerFactory;
+    // LoggerFactory expects providers to initialize their MDCAdapter field
+    // as early as possible, preferably at construction time.
+    private final MDCAdapter mdcAdapter;
+
+    public JULServiceProvider() {
+        markerFactory = new BasicMarkerFactory();
+        mdcAdapter = new BasicMDCAdapter();
+    }
 
     @Override
     public ILoggerFactory getLoggerFactory() {
@@ -42,7 +50,5 @@ public class JULServiceProvider implements SLF4JServiceProvider {
     @Override
     public void initialize() {
         loggerFactory = new JDK14LoggerFactory();
-        markerFactory = new BasicMarkerFactory();
-        mdcAdapter = new BasicMDCAdapter();
     }
 }

slf4j-jdk14/src/main/java9/module-info.java

@@ -2,5 +2,8 @@ module org.slf4j.jul {
   requires org.slf4j;
   requires java.logging;
   provides org.slf4j.spi.SLF4JServiceProvider with org.slf4j.jul.JULServiceProvider;
+
+  exports org.slf4j.jul;
+  opens org.slf4j.jul to org.slf4j;
 }
 

slf4j-jdk14/src/test/java/org/slf4j/issue/CallerInfoTest.java

@@ -19,6 +19,8 @@ import org.slf4j.event.SubstituteLoggingEvent;
 import org.slf4j.helpers.SubstituteLogger;
 import org.slf4j.helpers.SubstituteServiceProvider;
 import org.slf4j.jul.ListHandler;
+import org.slf4j.spi.CallerBoundaryAware;
+import org.slf4j.spi.LoggingEventBuilder;
 
 public class CallerInfoTest {
     Level oldLevel;
@@ -77,6 +79,22 @@ public class CallerInfoTest {
         assertEquals(this.getClass().getName(), logRecod.getSourceClassName());
     }
 
+    @Test
+    public void testCallerInfoWithFluentAPIAndAWrapper() {
+        Logger logger = LoggerFactory.getLogger("bla");
+        LoggingWrapper wrappedLogger = new LoggingWrapper(logger);
+
+        wrappedLogger.logWithEvent("hello");
+
+        List<LogRecord> recordList = listHandler.recordList;
+
+        assertEquals(1, recordList.size());
+
+        LogRecord logRecod = recordList.get(0);
+        assertEquals(this.getClass().getName(), logRecod.getSourceClassName());
+    }
+
+
     @Test
     public void testPostInitializationCallerInfoWithSubstituteLogger() {
         Logger logger = LoggerFactory.getLogger("bla");
@@ -119,4 +137,22 @@ public class CallerInfoTest {
         assertEquals(EventConstants.NA_SUBST, logRecod.getSourceClassName());
     }
 
+    static class LoggingWrapper {
+
+        Logger underlyingLogger;
+
+        LoggingWrapper(Logger aLogger) {
+            this.underlyingLogger = aLogger;
+        }
+        public void logWithEvent(String msg) {
+            LoggingEventBuilder lev = underlyingLogger.atInfo();
+            // setting the caller boundary to LoggingWrapper
+            if(lev instanceof CallerBoundaryAware) {
+                // builder is CallerBoundaryAware
+                ((CallerBoundaryAware) lev).setCallerBoundary(LoggingWrapper.class.getName());
+            }
+            lev.log(msg);
+        }
+    }
+
 }

slf4j-log4j12/pom.xml

@@ -8,7 +8,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
   
@@ -24,7 +24,7 @@
     <relocation>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-reload4j</artifactId>
-      <version>2.0.9</version>      
+      <version>2.0.18</version>      
     </relocation>
   </distributionManagement>
 

slf4j-migrator/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

slf4j-nop/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 
@@ -29,6 +29,14 @@
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>
     </dependency>
+
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-api</artifactId>
+      <type>test-jar</type>
+      <version>${project.version}</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
 </project>

slf4j-nop/src/main/java/org/slf4j/nop/NOPServiceProvider.java

@@ -18,9 +18,18 @@ public class NOPServiceProvider implements SLF4JServiceProvider {
     public static String REQUESTED_API_VERSION = "2.0.99"; // !final
 
     private final ILoggerFactory loggerFactory = new NOPLoggerFactory();
-    private final IMarkerFactory markerFactory = new BasicMarkerFactory();
-    private final MDCAdapter mdcAdapter = new NOPMDCAdapter();
 
+    // LoggerFactory expects providers to initialize markerFactory as early as possible.
+    private final IMarkerFactory markerFactory;
+    
+    // LoggerFactory expects providers to initialize their MDCAdapter field
+    // as early as possible, preferably at construction time.
+    private final MDCAdapter mdcAdapter;
+
+    public NOPServiceProvider() {
+        markerFactory = new BasicMarkerFactory();
+        mdcAdapter = new NOPMDCAdapter();
+    }
     public ILoggerFactory getLoggerFactory() {
         return loggerFactory;
     }
@@ -39,7 +48,6 @@ public class NOPServiceProvider implements SLF4JServiceProvider {
     }
 
     public void initialize() {
-
     }
 
    

slf4j-nop/src/main/java9/module-info.java

@@ -1,4 +1,7 @@
 module org.slf4j.nop { 
   requires org.slf4j;
   provides org.slf4j.spi.SLF4JServiceProvider with org.slf4j.nop.NOPServiceProvider;
+
+  exports org.slf4j.nop;
+  opens org.slf4j.nop to org.slf4j;
 }

slf4j-nop/src/test/java/org/slf4j/nop/MultithreadedInitializationTest.java

@@ -1,7 +1,7 @@
 /**
  * Copyright (c) 2004-2016 QOS.ch
  * All rights reserved.
- *
+ * <p>
  * Permission is hereby granted, free  of charge, to any person obtaining
  * a  copy  of this  software  and  associated  documentation files  (the
  * "Software"), to  deal in  the Software without  restriction, including
@@ -9,10 +9,10 @@
  * distribute,  sublicense, and/or sell  copies of  the Software,  and to
  * permit persons to whom the Software  is furnished to do so, subject to
  * the following conditions:
- *
+ * <p>
  * The  above  copyright  notice  and  this permission  notice  shall  be
  * included in all copies or substantial portions of the Software.
- *
+ * <p>
  * THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
  * EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
  * MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
@@ -20,29 +20,29 @@
  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  * OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- *
  */
 package org.slf4j.nop;
 
-import static org.junit.Assert.assertEquals;
-
-import java.io.PrintStream;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Random;
-import java.util.concurrent.BrokenBarrierException;
-import java.util.concurrent.CyclicBarrier;
-import java.util.concurrent.atomic.AtomicLong;
-
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.slf4j.LoggerFactoryFriend;
+import org.slf4j.helpers.StringPrintStream;
+
+import java.io.PrintStream;
+import java.util.Random;
+import java.util.concurrent.BrokenBarrierException;
+import java.util.concurrent.CyclicBarrier;
+import java.util.concurrent.atomic.AtomicLong;
+
+import static org.junit.Assert.assertEquals;
+import static org.slf4j.helpers.Reporter.SLF4J_INTERNAL_VERBOSITY_KEY;
 
 public class MultithreadedInitializationTest {
 
+    static int NUM_LINES_IN_SLF4J_CONNECTED_WITH_PROVIDER_INFO = 1;
     final static int THREAD_COUNT = 4 + Runtime.getRuntime().availableProcessors() * 2;
 
     private static final AtomicLong EVENT_COUNT = new AtomicLong(0);
@@ -52,16 +52,18 @@ public class MultithreadedInitializationTest {
     int diff = new Random().nextInt(10000);
     String loggerName = "org.slf4j.impl.MultithreadedInitializationTest";
     private final PrintStream oldErr = System.err;
-    StringPrintStream sps = new StringPrintStream(oldErr);
+    StringPrintStream sps = new StringPrintStream(oldErr, false);
 
     @Before
     public void setup() {
+        System.setProperty(SLF4J_INTERNAL_VERBOSITY_KEY, "debug");
         LoggerFactoryFriend.reset();
         System.setErr(sps);
     }
 
     @After
     public void tearDown() throws Exception {
+        System.clearProperty(SLF4J_INTERNAL_VERBOSITY_KEY);
         LoggerFactoryFriend.reset();
         System.setErr(oldErr);
     }
@@ -71,7 +73,7 @@ public class MultithreadedInitializationTest {
         System.out.println("THREAD_COUNT=" + THREAD_COUNT);
         LoggerAccessingThread[] accessors = harness();
 
-        for (LoggerAccessingThread accessor : accessors) {
+        for(LoggerAccessingThread accessor : accessors) {
             EVENT_COUNT.getAndIncrement();
             accessor.logger.info("post harness");
         }
@@ -80,19 +82,19 @@ public class MultithreadedInitializationTest {
         logger.info("hello");
         EVENT_COUNT.getAndIncrement();
 
-        assertEquals(0, sps.stringList.size());
+        assertEquals(NUM_LINES_IN_SLF4J_CONNECTED_WITH_PROVIDER_INFO, sps.stringList.size());
     }
 
     private static LoggerAccessingThread[] harness() throws InterruptedException, BrokenBarrierException {
         LoggerAccessingThread[] threads = new LoggerAccessingThread[THREAD_COUNT];
         final CyclicBarrier barrier = new CyclicBarrier(THREAD_COUNT + 1);
-        for (int i = 0; i < THREAD_COUNT; i++) {
+        for(int i = 0; i < THREAD_COUNT; i++) {
             threads[i] = new LoggerAccessingThread(barrier, i);
             threads[i].start();
         }
 
         barrier.await();
-        for (int i = 0; i < THREAD_COUNT; i++) {
+        for(int i = 0; i < THREAD_COUNT; i++) {
             threads[i].join();
         }
         return threads;
@@ -118,33 +120,35 @@ public class MultithreadedInitializationTest {
             logger.info("in run method");
             EVENT_COUNT.getAndIncrement();
         }
-    };
+    }
 
-    public static class StringPrintStream extends PrintStream {
+    ;
 
-        public static final String LINE_SEP = System.getProperty("line.separator");
-        PrintStream other;
-        List<String> stringList = new ArrayList<>();
-
-        public StringPrintStream(PrintStream ps) {
-            super(ps);
-            other = ps;
-        }
-
-        public void print(String s) {
-            other.print(s);
-            stringList.add(s);
-        }
-
-        public void println(String s) {
-            other.println(s);
-            stringList.add(s);
-        }
-
-        public void println(Object o) {
-            other.println(o);
-            stringList.add(o.toString());
-        }
-    };
+//    public static class StringPrintStream extends PrintStream {
+//
+//        public static final String LINE_SEP = System.getProperty("line.separator");
+//        PrintStream other;
+//        List<String> stringList = new ArrayList<>();
+//
+//        public StringPrintStream(PrintStream ps) {
+//            super(ps);
+//            other = ps;
+//        }
+//
+//        public void print(String s) {
+//            other.print(s);
+//            stringList.add(s);
+//        }
+//
+//        public void println(String s) {
+//            other.println(s);
+//            stringList.add(s);
+//        }
+//
+//        public void println(Object o) {
+//            other.println(o);
+//            stringList.add(o.toString());
+//        }
+//    };
 
 }

slf4j-reload4j/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 
@@ -51,7 +51,6 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-surefire-plugin</artifactId>
-        <version>2.19.1</version>
         <configuration>
           <forkCount>1</forkCount>
           <reuseForks>false</reuseForks>
@@ -61,7 +60,7 @@
             <exclude>**/AllTest.java</exclude>
             <exclude>**/PackageTest.java</exclude>
           </excludes>
-          <argLine>-Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8001</argLine>
+          <!--<argLine>-Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8001</argLine> -->
           <!--<argLine>XXadd-opens log4j/org.apache.log4j=org.slf4j.log4j12</argLine>-->
         </configuration>
       </plugin>

slf4j-reload4j/src/main/java/org/slf4j/reload4j/Reload4jServiceProvider.java

@@ -19,10 +19,17 @@ public class Reload4jServiceProvider implements SLF4JServiceProvider {
     public static String REQUESTED_API_VERSION = "2.0.99"; // !final
 
     private ILoggerFactory loggerFactory;
-    private IMarkerFactory markerFactory;
-    private MDCAdapter mdcAdapter;
+
+    // LoggerFactory expects providers to initialize markerFactory as early as possible.
+    private final IMarkerFactory markerFactory;
+
+    // LoggerFactory expects providers to have a valid MDCAdapter field
+    // as early as possible, preferably at construction time.
+    private final MDCAdapter mdcAdapter;
 
     public Reload4jServiceProvider() {
+        markerFactory = new BasicMarkerFactory();
+        mdcAdapter = new Reload4jMDCAdapter();
         try {
             @SuppressWarnings("unused")
             Level level = Level.TRACE;
@@ -34,8 +41,6 @@ public class Reload4jServiceProvider implements SLF4JServiceProvider {
     @Override
     public void initialize() {
         loggerFactory = new Reload4jLoggerFactory();
-        markerFactory = new BasicMarkerFactory();
-        mdcAdapter = new Reload4jMDCAdapter();
     }
 
     @Override

slf4j-simple/pom.xml

@@ -7,7 +7,7 @@
   <parent>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-parent</artifactId>
-    <version>2.0.10-SNAPSHOT</version>
+    <version>2.0.19-SNAPSHOT</version>
     <relativePath>../parent/pom.xml</relativePath>
   </parent>
 

slf4j-simple/src/main/java/org/slf4j/simple/SimpleLogger.java

@@ -221,10 +221,10 @@ public class SimpleLogger extends LegacyAbstractLogger {
     public static final String DEFAULT_LOG_LEVEL_KEY = SimpleLogger.SYSTEM_PREFIX + "defaultLogLevel";
 
     /**
-     * Package access allows only {@link SimpleLoggerFactory} to instantiate
+     * Protected access allows only {@link SimpleLoggerFactory} and also derived classes to instantiate
      * SimpleLogger instances.
      */
-    SimpleLogger(String name) {
+    protected SimpleLogger(String name) {
         this.name = name;
 
         String levelString = recursivelyComputeLevelString();
@@ -409,7 +409,7 @@ public class SimpleLogger extends LegacyAbstractLogger {
             buf.append('[');
 
         // Append a readable representation of the log level
-        String levelStr = level.name();
+        String levelStr = renderLevel(level.toInt());
         buf.append(levelStr);
         if (CONFIG_PARAMS.levelInBrackets)
             buf.append(']');
@@ -439,6 +439,22 @@ public class SimpleLogger extends LegacyAbstractLogger {
         write(buf, t);
     }
 
+    protected String renderLevel(int levelInt) {
+        switch (levelInt) {
+            case LOG_LEVEL_TRACE:
+                return "TRACE";
+            case LOG_LEVEL_DEBUG:
+                return("DEBUG");
+            case LOG_LEVEL_INFO:
+                return "INFO";
+            case LOG_LEVEL_WARN:
+                return CONFIG_PARAMS.warnLevelString;
+            case LOG_LEVEL_ERROR:
+                return "ERROR";
+        }
+        throw new IllegalStateException("Unrecognized level ["+levelInt+"]");
+    }
+
     public void log(LoggingEvent event) {
         int levelInt = event.getLevel().toInt();
 

slf4j-simple/src/main/java/org/slf4j/simple/SimpleLoggerFactory.java

@@ -47,28 +47,31 @@ public class SimpleLoggerFactory implements ILoggerFactory {
 
     /**
      * Return an appropriate {@link SimpleLogger} instance by name.
+     *
+     * This method will call {@link #createLogger(String)} if the logger
+     * has not been created yet.
      */
     public Logger getLogger(String name) {
-        Logger simpleLogger = loggerMap.get(name);
-        if (simpleLogger != null) {
-            return simpleLogger;
-        } else {
-            Logger newInstance = new SimpleLogger(name);
-            Logger oldInstance = loggerMap.putIfAbsent(name, newInstance);
-            return oldInstance == null ? newInstance : oldInstance;
-        }
+        return loggerMap.computeIfAbsent(name, this::createLogger);
+    }
+
+    /**
+     * Actually creates the logger for the given name.
+     */
+    protected Logger createLogger(String name) {
+        return new SimpleLogger(name);
     }
 
     /**
      * Clear the internal logger cache.
      *
-     * This method is intended to be called by classes (in the same package) for
-     * testing purposes. This method is internal. It can be modified, renamed or
-     * removed at any time without notice.
+     * This method is intended to be called by classes (in the same package or
+     * subclasses) for testing purposes. This method is internal. It can be
+     * modified, renamed or removed at any time without notice.
      *
      * You are strongly discouraged from calling this method in production code.
      */
-    void reset() {
+    protected void reset() {
         loggerMap.clear();
     }
 }

slf4j-simple/src/main/java/org/slf4j/simple/SimpleServiceProvider.java

@@ -17,8 +17,16 @@ public class SimpleServiceProvider implements SLF4JServiceProvider {
     public static String REQUESTED_API_VERSION = "2.0.99"; // !final
 
     private ILoggerFactory loggerFactory;
-    private IMarkerFactory markerFactory;
-    private MDCAdapter mdcAdapter;
+    // LoggerFactory expects providers to initialize markerFactory as early as possible.
+    private final IMarkerFactory  markerFactory;
+    // LoggerFactory expects providers to initialize their MDCAdapter field
+    // as early as possible, preferably at construction time.
+    private final MDCAdapter mdcAdapter;
+
+    public SimpleServiceProvider() {
+        markerFactory = new BasicMarkerFactory();
+        mdcAdapter =  new NOPMDCAdapter();
+    }
 
     public ILoggerFactory getLoggerFactory() {
         return loggerFactory;
@@ -41,10 +49,8 @@ public class SimpleServiceProvider implements SLF4JServiceProvider {
 
     @Override
     public void initialize() {
-
         loggerFactory = new SimpleLoggerFactory();
-        markerFactory = new BasicMarkerFactory();
-        mdcAdapter = new NOPMDCAdapter();
+
     }
 
 }

slf4j-simple/src/main/java9/module-info.java

@@ -1,4 +1,6 @@
-module org.slf4j.simple { 
+module org.slf4j.simple {
   requires org.slf4j;
   provides org.slf4j.spi.SLF4JServiceProvider with org.slf4j.simple.SimpleServiceProvider;
+  exports org.slf4j.simple;
+  opens org.slf4j.simple to org.slf4j;
 }

slf4j-simple/src/test/java/org/slf4j/simple/AcceptanceTest.java

@@ -0,0 +1,50 @@
+package org.slf4j.simple;
+
+import org.junit.Ignore;
+import org.slf4j.Logger;
+import org.slf4j.event.Level;
+
+import java.io.PrintStream;
+
+@Ignore
+public class AcceptanceTest extends LoggerTestSuite {
+
+    @Override
+    public Logger createLogger(ListAppendingOutputStream outputStream, Level level) {
+        SimpleLogger.CONFIG_PARAMS.outputChoice = new OutputChoice(new PrintStream(outputStream));
+
+        SimpleLogger logger = new SimpleLogger("TestSuiteLogger");
+        logger.currentLogLevel = SimpleLoggerConfiguration.stringToLevel(level.toString());
+        return logger;
+    }
+
+    @Override
+    public String extractMessage(String message) {
+        return message
+                .split("\n")[0]
+                .split("- ")[1];
+    }
+
+    @Override
+    public String extractExceptionMessage(String message) {
+        String[] logLines = message.split("\n");
+
+        if (logLines.length < 2) {
+            return null;
+        }
+        String exceptionLine = logLines[1];
+        return exceptionLine.split(": ")[1];
+    }
+
+    @Override
+    public String extractExceptionType(String message) {
+        String[] logLines = message.split("\n");
+
+        if (logLines.length < 2) {
+            return null;
+        }
+        String exceptionLine = logLines[1];
+        return exceptionLine.split(": ")[0];
+    }
+
+}

slf4j-simple/src/test/java/org/slf4j/simple/ConfigParamsTest.java

@@ -0,0 +1,53 @@
+package org.slf4j.simple;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.event.Level;
+
+import java.io.PrintStream;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Test class to verify configuration parameters of SimpleLogger
+ *
+ * @since 2.0.18
+ */
+public class ConfigParamsTest {
+
+
+    private ListAppendingOutputStream prepareSink(List<String> outputList) {
+        return new ListAppendingOutputStream(outputList);
+    }
+
+    @BeforeClass
+    static public void resetConfigParams() {
+        SimpleLogger.CONFIG_PARAMS.init();
+    }
+
+    public Logger createLogger(ListAppendingOutputStream outputStream, Level level, String warnLevelString) {
+        SimpleLogger.CONFIG_PARAMS.outputChoice = new OutputChoice(new PrintStream(outputStream));
+
+        SimpleLogger.CONFIG_PARAMS.warnLevelString = warnLevelString;
+
+        SimpleLogger logger = new SimpleLogger(ConfigParamsTest.class.getName());
+        logger.currentLogLevel = SimpleLoggerConfiguration.stringToLevel(level.toString());
+        return logger;
+    }
+
+    @Test
+    public void simpleTest(){
+        String WARN_LEVEL_STRING = "WXYZ";
+        ArrayList<String> outputList = new ArrayList<>();
+        Logger configuredLogger = createLogger(prepareSink(outputList), Level.TRACE,  WARN_LEVEL_STRING);
+
+        configuredLogger.warn("This is a test");
+
+        String str0 = outputList.get(0);
+        assertTrue(str0.contains(WARN_LEVEL_STRING));
+
+    }
+}

slf4j-simple/src/test/java/org/slf4j/simple/ListAppendingOutputStream.java

@@ -0,0 +1,25 @@
+package org.slf4j.simple;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.List;
+
+public class ListAppendingOutputStream extends OutputStream {
+
+    private final StringBuilder stringBuilder = new StringBuilder();
+    private final List<String> targetList;
+
+    ListAppendingOutputStream(List<String> list) {this.targetList = list;}
+
+
+    @Override
+    public void write(int b) throws IOException {
+        stringBuilder.append((char) b);
+    }
+
+    @Override
+    public void flush() {
+        targetList.add(stringBuilder.toString());
+        stringBuilder.delete(0, stringBuilder.length());
+    }
+}

slf4j-simple/src/test/java/org/slf4j/simple/LoggerTestSuite.java

@@ -0,0 +1,250 @@
+package org.slf4j.simple;
+
+
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.event.Level;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+
+public abstract class LoggerTestSuite {
+
+    private ListAppendingOutputStream prepareSink(List<String> outputList) {
+        return new ListAppendingOutputStream(outputList);
+    }
+
+    @Test
+    public void testTrace() {
+        ArrayList<String> outputList = new ArrayList<>();
+        Logger configuredLogger = createLogger(prepareSink(outputList), Level.TRACE);
+
+        assertTrue("Trace level should be enabled for this test", configuredLogger.isTraceEnabled());
+        configuredLogger.trace("Simple trace message");
+
+        assertEquals("Trace message should've been captured", 1, outputList.size());
+        assertTrue("Message should be logged in trace level", isTraceMessage(outputList.get(0)));
+        assertEquals("Supplied trace message wasn't found in the log",
+                     "Simple trace message",
+                     extractMessage(outputList.get(0)));
+
+        outputList.clear();
+
+        configuredLogger.debug("Simple debug message");
+        configuredLogger.info("Simple info message");
+        configuredLogger.warn("Simple warn message");
+        configuredLogger.error("Simple error message");
+        assertEquals("The other levels should have been captured", 4, outputList.size());
+
+    }
+
+    @Test
+    public void testDebug() {
+        ArrayList<String> outputList = new ArrayList<>();
+        Logger configuredLogger = createLogger(prepareSink(outputList), Level.DEBUG);
+
+        configuredLogger.trace("Simple trace message");
+        assertEquals("Lower levels should have been ignored", 0, outputList.size());
+
+        assertTrue("Debug level should be enabled for this test", configuredLogger.isDebugEnabled());
+        configuredLogger.debug("Simple debug message");
+
+        assertEquals("Debug message should've been captured", 1, outputList.size());
+        assertTrue("Message should be logged in debug level", isDebugMessage(outputList.get(0)));
+        assertEquals("Supplied debug message wasn't found in the log",
+                     "Simple debug message",
+                     extractMessage(outputList.get(0)));
+
+        outputList.clear();
+
+        configuredLogger.info("Simple info message");
+        configuredLogger.warn("Simple warn message");
+        configuredLogger.error("Simple error message");
+        assertEquals("The other levels should have been captured", 3, outputList.size());
+    }
+
+
+    @Test
+    public void testInfo() {
+        ArrayList<String> outputList = new ArrayList<>();
+        Logger configuredLogger = createLogger(prepareSink(outputList), Level.INFO);
+
+        configuredLogger.trace("Simple trace message");
+        configuredLogger.debug("Simple debug message");
+        assertEquals("Lower levels should have been ignored", 0, outputList.size());
+
+        assertTrue("Info level should be enabled for this test", configuredLogger.isInfoEnabled());
+        configuredLogger.info("Simple info message");
+
+        assertEquals("Info message should've been captured", 1, outputList.size());
+        assertTrue("Message should be logged in debug level", isInfoMessage(outputList.get(0)));
+        assertEquals("Supplied info message wasn't found in the log",
+                     "Simple info message",
+                     extractMessage(outputList.get(0)));
+
+        outputList.clear();
+
+        configuredLogger.warn("Simple warn message");
+        configuredLogger.error("Simple error message");
+        assertEquals("The other levels should have been captured", 2, outputList.size());
+    }
+
+    @Test
+    public void testWarn() {
+        ArrayList<String> outputList = new ArrayList<>();
+        Logger configuredLogger = createLogger(prepareSink(outputList), Level.WARN);
+
+        configuredLogger.trace("Simple trace message");
+        configuredLogger.debug("Simple debug message");
+        configuredLogger.info("Simple info message");
+        assertEquals("Lower levels should have been ignored", 0, outputList.size());
+
+        assertTrue("Warn level should be enabled for this test", configuredLogger.isWarnEnabled());
+        configuredLogger.warn("Simple warn message");
+
+        assertEquals("Warn message should've been captured", 1, outputList.size());
+        assertTrue("Message should be logged in warn level", isWarnMessage(outputList.get(0)));
+        assertEquals("Supplied warn message wasn't found in the log",
+                     "Simple warn message",
+                     extractMessage(outputList.get(0)));
+
+        outputList.clear();
+
+        configuredLogger.error("Simple error message");
+        assertEquals("The other levels should have been captured", 1, outputList.size());
+    }
+
+    @Test
+    public void testError() {
+        ArrayList<String> outputList = new ArrayList<>();
+        Logger configuredLogger = createLogger(prepareSink(outputList), Level.ERROR);
+
+        configuredLogger.trace("Simple trace message");
+        configuredLogger.debug("Simple debug message");
+        configuredLogger.info("Simple info message");
+        configuredLogger.warn("Simple warn message");
+        assertEquals("Lower levels should have been ignored", 0, outputList.size());
+
+        assertTrue("Error level should be enabled for this test", configuredLogger.isErrorEnabled());
+        configuredLogger.error("Simple error message");
+
+        assertEquals("Error message should've been captured", 1, outputList.size());
+        assertTrue("Message should be logged in error level", isErrorMessage(outputList.get(0)));
+        assertEquals("Supplied error message wasn't found in the log",
+                     "Simple error message",
+                     extractMessage(outputList.get(0)));
+    }
+
+    @Test
+    public void testFormatting() {
+        ArrayList<String> outputList = new ArrayList<>();
+        Logger configuredLogger = createLogger(prepareSink(outputList), Level.INFO);
+
+        configuredLogger.info("Some {} string", "formatted");
+        assertEquals("The formatted message should've been captured", 1, outputList.size());
+        assertEquals("Message should've been formatted", "Some formatted string", extractMessage(outputList.get(0)));
+    }
+
+    @Test
+    public void testException() {
+        ArrayList<String> outputList = new ArrayList<>();
+        Logger configuredLogger = createLogger(prepareSink(outputList), Level.INFO);
+
+        Exception exception = new RuntimeException("My error");
+
+        configuredLogger.info("Logging with an exception", exception);
+        assertEquals("The formatted message should've been captured", 1, outputList.size());
+        assertEquals("Message should've been formatted",
+                     "My error",
+                     extractExceptionMessage(outputList.get(0)));
+
+        assertEquals("Message should've been formatted",
+                     "java.lang.RuntimeException",
+                     extractExceptionType(outputList.get(0)));
+    }
+
+
+    /**
+     * Allows tests to check whether the log message contains a trace message.
+     * Override if needed.
+     * @param message String containing the full log message
+     * @return whether it is a trace message or not
+     */
+    protected boolean isTraceMessage(String message) {
+        return message.toLowerCase().contains("trace");
+    }
+
+    /**
+     * Allows tests to check whether the log message contains a debug message.
+     * Override if needed.
+     * @param message String containing the full log message
+     * @return whether it is a debug message or not
+     */
+    protected boolean isDebugMessage(String message) {
+        return message.toLowerCase().contains("debug");
+    }
+
+    /**
+     * Allows tests to check whether the log message contains an info message.
+     * Override if needed.
+     * @param message String containing the full log message
+     * @return whether it is an info message or not
+     */
+    protected boolean isInfoMessage(String message) {
+        return message.toLowerCase().contains("info");
+    }
+
+    /**
+     * Allows tests to check whether the log message contains a warn message.
+     * Override if needed.
+     * @param message String containing the full log message
+     * @return whether it is a warn message or not
+     */
+    protected boolean isWarnMessage(String message) {
+        return message.toLowerCase().contains("warn");
+    }
+
+    /**
+     * Allows tests to check whether the log message contains an error message.
+     * Override if needed.
+     * @param message String containing the full log message
+     * @return whether it is an error message or not
+     */
+    protected boolean isErrorMessage(String message) {
+        return message.toLowerCase().contains("error");
+    }
+
+    /**
+     * Extracts only the part of the log string that should represent the `message` string.
+     * @param message the full log message
+     * @return only the supplied message
+     */
+    public abstract String extractMessage(String message);
+
+    /**
+     * Extracts only the part of the log string that should represent the supplied exception message, if any.
+     * @param message the full log message
+     * @return only the supplied exception message
+     */
+    public abstract String extractExceptionMessage(String message);
+
+    /**
+     * Extracts only the part of the log string that should represent the supplied exception type.
+     * @param message the full log message
+     * @return only the supplied exception type name
+     */
+    public abstract String extractExceptionType(String message);
+
+    /**
+     * Configures the logger for running the tests.
+     * @param outputStream The output stream for logs to be written to
+     * @param level The expected level the tests will run for this logger
+     * @return a configured logger able to run the tests
+     */
+    public abstract Logger createLogger(ListAppendingOutputStream outputStream, Level level);
+
+}

slf4j-simple/src/test/java/org/slf4j/simple/SimpleLoggerMultithreadedInitializationTest.java

@@ -41,6 +41,8 @@ public class SimpleLoggerMultithreadedInitializationTest extends MultithreadedIn
     //
     // final int diff = new Random().nextInt(10000);
     static int NUM_LINES_IN_SLF4J_REPLAY_WARNING = 3;
+    static int NUM_LINES_IN_SLF4J_CONNECTED_WITH_PROVIDER_INFO = 1;
+
     private final PrintStream oldErr = System.err;
     final String loggerName = this.getClass().getName();
     StringPrintStream sps = new StringPrintStream(oldErr, false);
@@ -67,7 +69,7 @@ public class SimpleLoggerMultithreadedInitializationTest extends MultithreadedIn
 
     @Override
     protected int extraLogEvents() {
-        return NUM_LINES_IN_SLF4J_REPLAY_WARNING;
+        return NUM_LINES_IN_SLF4J_REPLAY_WARNING + NUM_LINES_IN_SLF4J_CONNECTED_WITH_PROVIDER_INFO;
     }
 
 }

slf4j-simple/src/test/java/org/slf4j/simple/Slf4jVersionTest.java

@@ -0,0 +1,21 @@
+package org.slf4j.simple;
+
+import org.junit.Test;
+import org.slf4j.helpers.Slf4jEnvUtil;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+public class Slf4jVersionTest {
+
+
+    @Test
+    public void slf4jVersionTest() {
+
+        String version = Slf4jEnvUtil.slf4jVersion();
+        assertNotNull(version);
+        assertTrue(version.startsWith("2"));
+
+    }
+
+}