add slf4j via log4j 2 logging

performanceDb/build.gradle

@@ -3,4 +3,10 @@ dependencies {
 	compile project(':pdb-api')
 	compile 'org.lucares:ludb:1.0.20170101101722'
 	compile 'com.fasterxml.jackson.core:jackson-databind:2.8.6'
+	
+	
+	
+	compile 'org.apache.logging.log4j:log4j-api:2.8'
+	compile 'org.apache.logging.log4j:log4j-core:2.8'
+	compile group: 'org.apache.logging.log4j', name: 'log4j-slf4j-impl', version: '2.8'
 }

performanceDb/src/main/java/org/lucares/performance/db/BlockingQueueIterator.java

@@ -3,8 +3,13 @@ package org.lucares.performance.db;
 import java.util.Optional;
 import java.util.concurrent.BlockingQueue;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 public final class BlockingQueueIterator<E> implements BlockingIterator<E> {
 
+	private static final Logger LOGGER = LoggerFactory.getLogger(BlockingQueueIterator.class);
+
 	private final BlockingQueue<E> queue;
 
 	private boolean closed = false;
@@ -23,9 +28,12 @@ public final class BlockingQueueIterator<E> implements BlockingIterator<E> {
 			return Optional.empty();
 		}
 
+		LOGGER.trace("wait for next entry");
 		final E next = queue.take();
+		LOGGER.trace("received entry: {}", next);
 
 		if (next == poison) {
+			LOGGER.trace("received poison");
 			closed = true;
 			return Optional.empty();
 		}

performanceDb/src/main/resources/log4j2.properties

@@ -0,0 +1,13 @@
+name = PropertiesConfig
+appenders = console
+ 
+ 
+appender.console.type = Console
+appender.console.name = STDOUT
+appender.console.layout.type = PatternLayout
+appender.console.layout.pattern = %d{yyyy-MM-dd HH:mm:ss.SSS} [%-5level] [%t] %c{1} - %msg%n
+ 
+ 
+ 
+rootLogger.level = trace
+rootLogger.appenderRef.stdout.ref = STDOUT