log4j - How to write log to multiple log files using log4j.properties

In Java applications some times you may need to write your log messages to specific log files with its own specific log properties. If you are using log4j internally then first step that you need to do is to have a proper log4j.properties file.

Below example shows 2 log4j appenders which write to 2 different log files, one is a debug log and another one is a reports log. Debug log file can have all log messages and reports log can have log messages specific to reporting on say splunk monitoring.

# Root logger option  
 log4j.rootLogger=ALL,STDOUT,debugLog  
 log4j.logger.reportsLogger=INFO,reportsLog  
 log4j.additivity.reportsLogger=false 

 log4j.appender.STDOUT=org.apache.log4j.ConsoleAppender  
 log4j.appender.STDOUT.layout=org.apache.log4j.PatternLayout  
 log4j.appender.STDOUT.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %C:%L - %m%n 

 # Direct log messages to a log file  
 log4j.appender.debugLog=org.apache.log4j.RollingFileAppender  
 log4j.appender.debugLog.File="/Users/test/debuglog.log"  
 log4j.appender.debugLog.MaxFileSize=10MB  
 log4j.appender.debugLog.MaxBackupIndex=10  
 log4j.appender.debugLog.layout=org.apache.log4j.PatternLayout  
 log4j.appender.debugLog.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %C:%L - %m%n 

# Direct log messages to a log file  
 log4j.appender.reportsLog=org.apache.log4j.RollingFileAppender  
 log4j.appender.reportsLog.File="/Users/test/reportslog.log"  
 log4j.appender.reportsLog.MaxFileSize=10MB  
 log4j.appender.reportsLog.MaxBackupIndex=10  
 log4j.appender.reportsLog.layout=org.apache.log4j.PatternLayout  
 log4j.appender.reportsLog.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %C:%L - %m%n  

Here we defined a rootLogger which is the default logger where all messages will go to except those are designated for reportsLogger.

log4j.logger.reportsLogger=INFO,reportsLog -  indicates reportsLog appender will log INFO messages and up.

In Java Code you will initialize loggers as below. Here I am using Apache commons logging which is using log4j under the hood.

package com.developertrciks;  
   
 import org.apache.commons.logging.Log;  
 import org.apache.commons.logging.LogFactory;  
   
 public class MyTestClass {  
        
      private static Log log= LogFactory.getLog("debugLogger");  
      private static Log reportsLog= LogFactory.getLog("reportsLogger");  
        
      public void logTester() {  
           log.debug("debug log message");  
           reportsLog.debug("reports debug message");  
           reportsLog.info("reports info message");  
      }  
   
       public static void main(String[] args) {  
             
           MyTestClass test = new MyTestClass();  
           test.logTester();  
           System.out.println("completed successfully");  
             
      }  
 }