Add trigger examples

patch by Vijay; reviewed by jbellis for CASSANDRA-5574

examples/triggers/README.txt

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+Cassandra Trigger's Example:
+=========================
+
+InvertedIndex class will create a inverted index of 
+RowKey:ColumnName:Value to Value:ColumnName:RowKey
+
+NOTE: This example is limited to append-only workloads, 
+	  doesn't delete indexes on deletes. 
+
+Installation:
+============
+change directory to <cassandra_src_dir>/examples/triggers
+run "ant jar"
+Copy build/trigger-example.jar to <cassandra_home>/triggers/
+Copy conf/* to <cassandra_home>/conf/
+Create column family configured in InvertedIndex.properties 
+    Example: Keyspace1.InvertedIndex as configured in InvertedIndex.properties
+Configure trigger on the table.
+    Example: CREATE TRIGGER test1 ON "Keyspace1"."Standard1" 
+                    EXECUTE ('org.apache.cassandra.triggers.InvertedIndex');
+Start inserting data to the column family which has the triggers. 

examples/triggers/build.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project default="jar" name="trigger-example">
+	<property name="cassandra.dir" value="../.." />
+	<property name="cassandra.dir.lib" value="${cassandra.dir}/lib" />
+	<property name="cassandra.classes" value="${cassandra.dir}/build/classes/main" />
+	<property name="build.src" value="${basedir}/src" />
+	<property name="build.dir" value="${basedir}/build" />
+	<property name="build.classes" value="${build.dir}/classes" />
+	<property name="final.name" value="trigger-example" />
+
+	<path id="build.classpath">
+		<fileset dir="${cassandra.dir.lib}">
+			<include name="**/*.jar" />
+		</fileset>
+		<fileset dir="${cassandra.dir}/build/lib/jars">
+			<include name="**/*.jar" />
+		</fileset>
+		<pathelement location="${cassandra.classes}" />
+	</path>
+	<target name="init">
+		<mkdir dir="${build.classes}" />
+	</target>
+
+	<target name="build" depends="init">
+		<javac destdir="${build.classes}" debug="true" includeantruntime="false">
+			<src path="${build.src}" />
+			<classpath refid="build.classpath" />
+		</javac>
+	</target>
+
+	<target name="jar" depends="build">
+		<jar jarfile="${build.dir}/${final.name}.jar">
+			<fileset dir="${build.classes}" />
+		</jar>
+	</target>
+
+	<target name="clean">
+		<delete dir="${build.dir}" />
+	</target>
+</project>

examples/triggers/conf/InvertedIndex.properties

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+keyspace=Keyspace1
+columnfamily=InvertedIndex

examples/triggers/src/org/apache/cassandra/triggers/InvertedIndex.java

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+package org.apache.cassandra.triggers;
+
+import java.io.InputStream;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.Properties;
+
+import org.apache.cassandra.db.ColumnFamily;
+import org.apache.cassandra.db.RowMutation;
+import org.apache.cassandra.io.util.FileUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class InvertedIndex implements ITrigger {
+    private static final Logger logger = LoggerFactory.getLogger(InvertedIndex.class);
+    private Properties properties = loadProperties();
+
+    public Collection<RowMutation> augment(ByteBuffer key, ColumnFamily update) {
+        List<RowMutation> mutations = new ArrayList<RowMutation>();
+        for (ByteBuffer name : update.getColumnNames()) {
+            RowMutation mutation = new RowMutation(properties.getProperty("keyspace"), update.getColumn(name).value());
+            mutation.add(properties.getProperty("columnfamily"), name, key, System.currentTimeMillis());
+            mutations.add(mutation);
+        }
+        return mutations;
+    }
+
+    private static Properties loadProperties() {
+        Properties properties = new Properties();
+        InputStream stream = InvertedIndex.class.getClassLoader().getResourceAsStream("InvertedIndex.properties");
+        try {
+            properties.load(stream);
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        } finally {
+            FileUtils.closeQuietly(stream);
+        }
+        logger.info("loaded property file, InvertedIndex.properties");
+        return properties;
+    }
+}