How to Trace Program Flow using Log4j2

Background

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Do you not hate it to log method with “entry” and “exit” texts? Should you use “start” or “entry”? This article demonstrates how to use Log4j2 API to perform flow tracing without the need to provide texts.

Software Environment

Windows 7 Professional SP1
Eclipse – Kepler Release
Java 1.7 (1.7.0_67 – Windows x86)
Apache Log4j 2.0.2

Download Log4j2 and Reference it

Download log4j2 from http://logging.apache.org/log4j/2.x/
Extract the file
Copy the log4j-api-2.0.2.jar and log4j-core-2.0.2.jar to your Eclipse project
Reference the two jar files

Define your log4j2.xml

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Define log4j2.xml and place it right under the src folder (visible also via Eclipse workspace)

<?xml version="1.0" encoding="UTF-8"?>
<configuration status="error">
  <appenders>
    <console name="Console" target="SYSTEM_OUT">
      <thresholdfilter level="ERROR" onmatch="ACCEPT" onmismatch="DENY">
      <!-- Flow tracing is most useful with a pattern that shows location.
           Below pattern outputs class, line number and method name. -->
      <patternlayout pattern="%d{HH:mm:ss.SSS} %-5level %class{36} %L %M - %msg%xEx%n">
    </patternlayout></thresholdfilter></console>
    <file append="false" filename="logs/test.log" name="log">
      <patternlayout pattern="%d{HH:mm:ss.SSS} %-5level %class{36} %L %M - %msg%xEx%n">
    </patternlayout></file>
  </appenders>
  <loggers>
    <root level="trace">
      <appenderref ref="log">
    </appenderref></root>
  </loggers>
</configuration>

<?xml version="1.0" encoding="UTF-8"?>

<!-- Flow tracing is most useful with a pattern that shows location.

Below pattern outputs class, line number and method name. -->

</patternlayout></thresholdfilter></console>

</patternlayout></file>

</appenders>

</appenderref></root>

</loggers>

</configuration>

Sample Usage

/*
 * Copyright (C) 2014 www.turreta.com
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.turreta.apache.log4j2;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class LogProgramFlowSample {
	
	private Logger logger = LogManager.getLogger(LogProgramFlowSample.class.getName());
	
	public void doItA() {
		logger.entry();
		this.doItB();
		logger.exit();
	}
	
	private void doItB() {
		logger.entry();
		this.doItC();
		logger.exit();
	}
	
	private void doItC() {
		logger.entry();
		System.out.println("DONE");
		logger.exit();
	}
	
	
	public static void main(String[] args) {
		LogProgramFlowSample sample = new LogProgramFlowSample();
		sample.doItA();
	}
}

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

* http://www.apache.org/licenses/LICENSE-2.0

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

package com.turreta.apache.log4j2;

import org.apache.logging.log4j.LogManager;

import org.apache.logging.log4j.Logger;

public class LogProgramFlowSample {

private Logger logger = LogManager.getLogger(LogProgramFlowSample.class.getName());

public void doItA() {

logger.entry();

this.doItB();

logger.exit();

}

private void doItB() {

logger.entry();

this.doItC();

logger.exit();

}

private void doItC() {

logger.entry();

System.out.println("DONE");

logger.exit();

}

public static void main(String[] args) {

LogProgramFlowSample sample = new LogProgramFlowSample();

sample.doItA();

}

Sample Output

01:18:23.175 TRACE com.turreta.apache.log4j2.LogProgramFlowSample 27 doItA - entry
01:18:23.176 TRACE com.turreta.apache.log4j2.LogProgramFlowSample 33 doItB - entry
01:18:23.176 TRACE com.turreta.apache.log4j2.LogProgramFlowSample 39 doItC - entry
01:18:23.176 TRACE com.turreta.apache.log4j2.LogProgramFlowSample 41 doItC - exit
01:18:23.176 TRACE com.turreta.apache.log4j2.LogProgramFlowSample 35 doItB - exit
01:18:23.176 TRACE com.turreta.apache.log4j2.LogProgramFlowSample 29 doItA - exit