In SLF4JProviders, move initialization of the markerFactory and

mdcAdapter fields to the constructor.

Added comments regarding LoggerFactory expectation of providers to
initialize their MDCAdapter and markerFactory field as early as
possible, preferably at construction time.

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

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

@@ -220,8 +220,8 @@ public final class LoggerFactory {
     /**
      * The value of PROVIDER.getMDCAdapter() can be null while PROVIDER has not yet initialized.
      *
-     * However,
-     *
+     * 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();

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-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 = new BasicMarkerFactory();
-    private 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 JULServiceProvider() {
+        markerFactory = new BasicMarkerFactory();
+        mdcAdapter = new BasicMDCAdapter();
+    }
 
     @Override
     public ILoggerFactory getLoggerFactory() {

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-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 = new BasicMarkerFactory();
-    private MDCAdapter mdcAdapter = new Reload4jMDCAdapter();
+
+    // 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;

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  = new BasicMarkerFactory();
-    private 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 SimpleServiceProvider() {
+        markerFactory = new BasicMarkerFactory();
+        mdcAdapter =  new NOPMDCAdapter();
+    }
 
     public ILoggerFactory getLoggerFactory() {
         return loggerFactory;
@@ -42,6 +50,7 @@ public class SimpleServiceProvider implements SLF4JServiceProvider {
     @Override
     public void initialize() {
         loggerFactory = new SimpleLoggerFactory();
+
     }
 
 }