Log4J MDC, Log4J2 MDC samples added.

log-mdc-ndc/README.md

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+### Relevant Articles:
+- TBD
+
+### References
+
+_Log4j MDC_
+* <https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/MDC.html>
+* <http://veerasundar.com/blog/2009/10/log4j-mdc-mapped-diagnostic-context-what-and-why/>
+
+_Log4j2_
+* <https://logging.apache.org/log4j/2.x/manual/thread-context.html>
+
+

log-mdc-ndc/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>com.baeldug</groupId>
+	<artifactId>logmdcndc</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<name>logmdcndc</name>
+	<description>tutorial on logging with MDC and NDC</description>
+
+	<dependencies>
+		<!--log4j dependencies -->
+		<dependency>
+			<groupId>log4j</groupId>
+			<artifactId>log4j</artifactId>
+			<version>1.2.17</version>
+		</dependency>
+		
+        <!--log4j2 dependencies-->
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-api</artifactId>
+            <version>2.7</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-core</artifactId>
+            <version>2.7</version>
+        </dependency>
+        
+		<!--disruptor for log4j2 async logging-->
+        <dependency>
+            <groupId>com.lmax</groupId>
+            <artifactId>disruptor</artifactId>
+            <version>3.3.4</version>
+        </dependency>
+        
+	</dependencies>
+
+</project>

log-mdc-ndc/src/main/java/com/baeldung/mdc/BusinessService.java

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+package com.baeldung.mdc;
+
+public interface BusinessService {
+
+	void businessMethod(String transactionId);
+
+}

log-mdc-ndc/src/main/java/com/baeldung/mdc/TransactionContext.java

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+package com.baeldung.mdc;
+
+import java.util.Date;
+
+public class TransactionContext {
+	
+	private String transactionId;
+	private String owner;
+	private Date createdAt;
+	
+	public TransactionContext(String transactionId, String owner) {
+		this.transactionId = transactionId;
+		this.owner = owner;
+		this.createdAt = new Date();
+	}
+
+	public String getOwner() {
+		return owner;
+	}
+
+	public String getTransactionId() {
+		return transactionId;
+	}
+	
+	public Date getCreatedAt() {
+		return createdAt;
+	}
+	
+}

log-mdc-ndc/src/main/java/com/baeldung/mdc/log4j/Log4jBusinessService.java

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+package com.baeldung.mdc.log4j;
+
+import org.apache.log4j.Logger;
+
+import com.baeldung.mdc.BusinessService;
+
+public class Log4jBusinessService implements BusinessService {
+	
+	private final static Logger logger = Logger.getLogger(Log4jBusinessService.class);
+	
+	@Override
+	public void businessMethod(String transactionId) {
+		logger.info("Executing transaction #" + transactionId );
+	}
+	
+}

log-mdc-ndc/src/main/java/com/baeldung/mdc/log4j/Log4jDemo.java

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+package com.baeldung.mdc.log4j;
+
+public class Log4jDemo {
+	
+	public static void main(String[] args) throws InterruptedException {
+		Log4jExecutor greeter = new Log4jExecutor();
+		Thread thread1 = new Thread(greeter);
+		Thread thread2 = new Thread(greeter);
+		
+		thread1.start();
+		thread2.start();
+		
+		thread1.join();
+		thread2.join();
+	}
+
+}

log-mdc-ndc/src/main/java/com/baeldung/mdc/log4j/Log4jExecutor.java

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+package com.baeldung.mdc.log4j;
+
+import org.apache.log4j.Logger;
+import org.apache.log4j.MDC;
+
+import com.baeldung.mdc.TransactionContext;
+
+public class Log4jExecutor implements Runnable {
+	
+	public void run() {
+
+		String transactionId = "" + Math.random();
+		String owner = "owner" + Math.random();
+		TransactionContext ctx = new TransactionContext(transactionId, owner);
+
+		MDC.put("transaction.id", transactionId);
+		MDC.put("transaction.owner", owner);
+		MDC.put("transaction.createdAt", ctx.getCreatedAt());
+
+		new Log4jBusinessService().businessMethod(ctx.getTransactionId());
+	}
+
+}

log-mdc-ndc/src/main/java/com/baeldung/mdc/log4j2/Log4j2BusinessService.java

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+package com.baeldung.mdc.log4j2;
+
+
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+import com.baeldung.mdc.BusinessService;
+
+public class Log4j2BusinessService implements BusinessService {
+	
+	private static final Logger logger = LogManager.getLogger(); //Log4j2BusinessService.class);
+	
+	@Override
+	public void businessMethod(String transactionId) {
+		logger.info("Executing transaction #{}", transactionId );
+	}
+	
+}

log-mdc-ndc/src/main/java/com/baeldung/mdc/log4j2/Log4j2Demo.java

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+package com.baeldung.mdc.log4j2;
+
+public class Log4j2Demo {
+	
+	public static void main(String[] args) throws InterruptedException {
+		Log4j2Executor greeter = new Log4j2Executor();
+		Thread thread1 = new Thread(greeter);
+		Thread thread2 = new Thread(greeter);
+		
+		thread1.start();
+		thread2.start();
+		
+		thread1.join();
+		thread2.join();
+	}
+
+}

log-mdc-ndc/src/main/java/com/baeldung/mdc/log4j2/Log4j2Executor.java

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+package com.baeldung.mdc.log4j2;
+
+import org.apache.logging.log4j.ThreadContext;
+
+import com.baeldung.mdc.TransactionContext;
+
+public class Log4j2Executor implements Runnable {
+	
+	public void run() {
+
+		String transactionId = "" + Math.random();
+		String owner = "owner" + Math.random();
+		TransactionContext ctx = new TransactionContext(transactionId, owner);
+		
+		ThreadContext.put("transaction.id", transactionId);
+		ThreadContext.put("transaction.owner", owner);
+		ThreadContext.put("transaction.createdAt", ctx.getCreatedAt().toString());
+
+		new Log4j2BusinessService().businessMethod(ctx.getTransactionId());
+	}
+
+}

log-mdc-ndc/src/main/resources/log4j.properties

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+log4j.appender.consoleAppender=org.apache.log4j.ConsoleAppender
+log4j.appender.consoleAppender.layout=org.apache.log4j.PatternLayout
+
+log4j.appender.file=org.apache.log4j.FileAppender
+log4j.appender.file.File=/tmp/$X{transaction.owner}
+log4j.appender.file.layout=org.apache.log4j.PatternLayout
+
+#note the %X{userName} - this is how you fetch data from Mapped Diagnostic Context (MDC)
+log4j.appender.consoleAppender.layout.ConversionPattern=%-4r [%t] %5p %c %x - %m - owner=%X{transaction.owner} creation=%X{transaction.createdAt}%n
+log4j.appender.file.layout.ConversionPattern=%-4r [%t] %5p %c %x - %m - owner=%X{transaction.owner} creation=%X{transaction.createdAt}%n
+
+log4j.rootLogger = ALL, consoleAppender, file

log-mdc-ndc/src/main/resources/log4j2.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<Configuration status="INFO">
+    <Appenders>
+        # Console appender
+        <Console name="stdout" target="SYSTEM_OUT">
+            # Pattern of log message for console appender
+            <PatternLayout pattern="Log4j2 - %d{yyyy-MM-dd HH:mm:ss} %p %m owner=%X{transaction.owner} creation=%X{transaction.createdAt}%n"/>
+        </Console>
+
+        # File appender
+        <!--  
+        
+        <File name="fout" fileName="log4j/target/baeldung-log4j2.log" immediateFlush="false" append="false">
+            # Pattern of log message for file appender
+            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} %p %m%n"/>
+        </File>
+        -->
+    </Appenders>
+
+    <Loggers>
+        # Override log level for specified package
+        <Logger name="com.baeldung.log4j2" level="TRACE"/>
+
+        <AsyncRoot level="DEBUG">
+            <AppenderRef ref="stdout"/>
+            <!--  
+            
+            <AppenderRef ref="fout"/>
+            -->
+        </AsyncRoot>
+    </Loggers>
+</Configuration>