Integrate Log4j With Your Application

Introduction

Logging is the process of writing log messages during the execution of a program to a central place. Application log is very important for code debugging and data analysis. Log4J is the most populalar logging framework

The following table defines the log levels and messages in log4j, in decreasing order of severity.

Objectives

• Log file path and it’s properties (i.e. max log file size, max backup index etc) to be defined
• Two log files will get generated for two different packages
• The log will get printed on the CONSOLE as well
• Use of custom log file appender for the 2nd log file instead of the default one. Custom appender will add the time stamp with the log file

Steps to Integrate property file based Log4J

• Create a simple java project with src/main/java, src/main/resources as the source directory. Once project is created, you can add source directory from the below screen (Right click on project -> properties)
  
• Convert the project into maven project (Right click on the project -> Configure -> Convert to Maven project)
• Add the following dependancies in your pom.xml for log4J integration

	<dependencies>
		<dependency>
			<groupId>commons-logging</groupId>
			<artifactId>commons-logging</artifactId>
			<version>1.1</version>
	    </dependency>
		<dependency>
			<groupId>log4j</groupId>
			<artifactId>log4j</artifactId>
			<version>1.2.14</version>
		</dependency>
	</dependencies>

• Create 4 files as shown below

purpose of each file is described in the below table

Code inside the each file is given below. Please go through the inline comments with the code snippets

• log4j.properties: log4j configuration is done here. Please go through the inline comments to understand the configuration

#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# OBJECTIVES
# 1. Log file path and it's properties 
#	 (i.e. max log file size, max backup index etc) to be defined
# 2. Two log files will get generated for two different packages
# 3. The log will get printed on the CONSOLE as well
# 4. Use of custom log file appender for the 2nd log file 
#    instead of the default one. Custom appender will add 
#	 the time stamp with the log file
#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


#****************************************************
# Root logger option. To change log level, change here
# Log level is TRACE. Log will be printed on CONSOLE and 
# log file as configured in log4j.appender.logfile
#****************************************************
log4j.rootLogger=TRACE, CONSOLE, logfile

#****************************************************
# Package logger option
# Log level is FATAL. Log will be printed on CONSOLE and 
# log file as configured in log4j.appender.logfile
#****************************************************
log4j.logger.com.ashish.anotherpackage=FATAL, another


#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# Redirect log messages to CONSOLE
#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Target=System.out
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
#*****
#Below configuration append "2015-05-21 16:06:42 <LEVEL>  Log4JIntegration:16" before the message
#*****
log4j.appender.CONSOLE.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n
 

#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# Redirect log messages to a log file, support file rolling.
#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
log4j.appender.logfile=org.apache.log4j.RollingFileAppender
#log4j.appender.logfile=com.ashish.customlog4j.CustomLog4JAppender
log4j.appender.logfile.File=D:\\logs\\output.log
log4j.appender.logfile.Append=true
log4j.appender.logfile.MaxFileSize=2MB
log4j.appender.logfile.MaxBackupIndex=10
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
#*****
#Below configuration append "2015-05-21 16:06:42 <LEVEL>  Log4JIntegration:16" before the message
#*****
log4j.appender.logfile.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n


#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# Another Log file for another package
#++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

log4j.appender.another=com.ashish.customlog4j.CustomLog4JAppender
log4j.appender.another.File=D:\\logs\\output_another.log
log4j.appender.another.layout=org.apache.log4j.PatternLayout
#*****
#Below configuration append "2015-05-21 16:06:42 <LEVEL>  Log4JIntegration:16" before the message
#*****
log4j.appender.another.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

• Log4JIntegration: Log level is set to TRACE so this class will print all logs.

package com.ashish.log4jIntegration;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.log4j.LogManager;
import com.ashish.anotherpackage.AnotherClass;

public class Log4JIntegration {
	// org.apache.commons.logging.Log and org.apache.log4j.spi.LoggerFactory comes from commons-logging.jar
	private static final Log LOG = LogFactory.getLog(Log4JIntegration.class);
	public static void main(String args[]) {
		// Want to print this below line always. So LOG.fatal() is used
		LOG.fatal("Log level; for com.ashish.log4jIntegration package is : " + LogManager.getRootLogger().getLevel());
		LOG.trace("TRACE: Rank 6");
		LOG.debug("DEBUG: Rank 5");
		LOG.info("INFO: Rank 4");
		LOG.warn("WARN: Rank 3");
		LOG.error("ERROR: Rank 2");
		LOG.fatal("FATAL: Rank 1");
		
		AnotherClass.anotherMethod();
	}
}

• AnotherClass: Log level is set to FATAL so this class will print only LOG.fatal() and ignores other logs

package com.ashish.anotherpackage;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.log4j.LogManager;

public class AnotherClass {
	// org.apache.commons.logging.Log and org.apache.log4j.spi.LoggerFactory comes from commons-logging.jar
	private static final Log LOG = LogFactory.getLog(AnotherClass.class);
	public static void anotherMethod() {
		LOG.fatal("Log level; for com.ashish.anotherpackage package is : " + LogManager.getLogger(AnotherClass.class).getEffectiveLevel());
		LOG.trace("TRACE: Rank 6");
		LOG.debug("DEBUG: Rank 5");
		LOG.info("INFO: Rank 4");
		LOG.warn("WARN: Rank 3");
		LOG.error("ERROR: Rank 2");
		LOG.fatal("FATAL: Rank 1");
	}
}

• CustomLog4JAppender: In every execution this class creates new file by appending timestamp with the log file name.

package com.ashish.customlog4j;

import java.io.File;
import java.io.IOException;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.apache.log4j.Layout;
import org.apache.log4j.RollingFileAppender;
import org.apache.log4j.spi.ErrorCode;



public class CustomLog4JAppender extends RollingFileAppender  {
	public CustomLog4JAppender() {
	}
	
	public CustomLog4JAppender(Layout layout, String filename,
	        boolean append) throws IOException {
	    super(layout, filename, append);
	}

	public CustomLog4JAppender(Layout layout, String filename)
	        throws IOException {
	    super(layout, filename);
	}
	
	public void activateOptions() {
		if (fileName != null) {
		    try {
		    	fileName = getNewLogFileName();
		        setFile(fileName, fileAppend, bufferedIO, bufferSize);
		    } catch (Exception e) {
		        errorHandler.error("Error while activating log options", e,
		                ErrorCode.FILE_OPEN_FAILURE);
		    }
		}
		}

		private String getNewLogFileName() {
			DateFormat df = new SimpleDateFormat("dd-MMM-yyyy-HH-mm-ss");
			
			if (fileName != null) {
			    final String DOT = ".";
			    final String HIPHEN = "-";
			    final File currentLogFile = new File(fileName);
			    final String fileName = currentLogFile.getName();
			    String newLogFileName = fileName;
			    
			    final int dotIndex = fileName.indexOf(DOT);
			    if (dotIndex != -1) {
			        // the file name has an extension. so, insert the time stamp
			        // between the file name and the extension
			        newLogFileName = fileName.substring(0, dotIndex)  + HIPHEN +
			                   df.format(new Date())  + DOT +
			                  fileName.substring(dotIndex+1);
			    } else {
			        // the file name has no extension. So, just append the timestamp
			        // at the end.
			        newLogFileName = fileName + HIPHEN  + System.currentTimeMillis();
			    }
			    return currentLogFile.getParent() + File.separator + newLogFileName;
			}
			return null;
		}
}

Output of this project

• Console output will look like as shown below. Two classes, Log4JIntegration and AnotherClass have same log messages but log level is configured differently (TRACE and FATAL respectively) for two different classes. Hence the Log4JIntegration class is printing all log messages and AnotherClass is printing only one message.

• Two log files got created. One file name is without time stamp (e.g.: output.log) and another log file name is with time stamp appended (e.g. output_another-21-May-2015-16-39-59.log) in it and have multiple copies. Log files will get created under D:\logs\ folder as configured in the log4j.properties file. The log from Log4JIntegration class goes to output.log file and the logs from AnotherClass class goes to output_another-21-May-2015-16-39-59.log file. Also note that both the mentioned classes prints the log message in CONSOLE.

Steps to Integrate XML based Log4J

Remove the log4j.properties file and create log4j.xml file at the same location with the below content. Go through the inline comments to understand the configuration

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration debug="true"
  xmlns:log4j='http://jakarta.apache.org/log4j/'>
 
 	<!-- Redirect log messages to CONSOLE -->
	<appender name="CONSOLE" class="org.apache.log4j.ConsoleAppender">
		<param name="target" value="System.out" />
	    <layout class="org.apache.log4j.PatternLayout">
			<param name="ConversionPattern" 
				value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
	    </layout>
	</appender>
 
 	<!-- Redirect log messages to a log file, support file rolling. -->
	<appender name="logfile" class="org.apache.log4j.RollingFileAppender">
		<param name="file" value="D:/logs/output.log" />
	    <param name="append" value="true" />
	    <param name="maxFileSize" value="2MB" />
	    <param name="maxBackupIndex" value="10" />
	    <layout class="org.apache.log4j.PatternLayout">
			<param name="ConversionPattern" 
				value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
	    </layout>
	</appender>
	
	<!-- Another Log file for another package -->
	<appender name="another" class="com.ashish.customlog4j.CustomLog4JAppender">
		<param name="file" value="D:/logs/output_another.log" />
	    <param name="append" value="true" />
	    <param name="maxFileSize" value="2MB" />
	    <param name="maxBackupIndex" value="10" />
	    <layout class="org.apache.log4j.PatternLayout">
			<param name="ConversionPattern" 
				value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
	    </layout>
	</appender>
 
 	<!-- 
 		Package logger option Log level is FATAL. Log will be printed on CONSOLE and log file as configured in log4j.appender.logfile
 	-->
 	<logger name="com.ashish.anotherpackage.AnotherClass">
	  	<level value="FATAL"/> 
		<appender-ref ref="another" />
	</logger>
	
	<!-- 
	Root logger option. To change log level, change here Log level is TRACE. Log will be printed on CONSOLE and log file as configured in log4j.appender.logfile
	 -->
	<root>
		<level value="TRACE" />
		<appender-ref ref="CONSOLE" />
		<appender-ref ref="logfile" />
	</root>
	
</log4j:configuration>