Writing to Different Log Files Example using Log4j

One of the common requirement in Java projects, that are using Log4j, and want to write logs into different files for each module (or layer) in the project. For example, if you have a an application and you may want to log the messages from the service layer to a service.log file and the log messages from the DAO layer to the DAO.log file and so on. This is very simple to achieve using Log4j. EVEN you can differentiate logs for EACH Java class with the project.

log.properties

# Root logger option

log4j.rootLogger=INFO, stdout, file



# Redirect log messages to console

log4j.appender.stdout=org.apache.log4j.ConsoleAppender

log4j.appender.stdout.Target=System.out

log4j.appender.stdout.layout=org.apache.log4j.PatternLayout

log4j.appender.stdout.layout.ConversionPattern=[%d{yyyy-MM-dd HH:mm:ss}] %-5p %m%n



# Redirect log messages to a log file, support file rolling.

log4j.appender.file=org.apache.log4j.RollingFileAppender

log4j.appender.file.File=logs/default_Logs.log

log4j.appender.file.MaxFileSize=10MB

log4j.appender.file.MaxBackupIndex=5

log4j.appender.file.layout=org.apache.log4j.PatternLayout

log4j.appender.file.layout.ConversionPattern=[%d{yyyy-MM-dd HH\:mm\:ss}] %-5p %m%n

Now call the below method loadLog4jConfig(this) from the class for which you want to differentiate log file. A common practice is to call the below method from the constructor of the class. It will runtime generate a log file named as that of class name and will write all corresponding logs into this particular log file. 

public static void loadLog4jConfig(Object obj)

 {

 try

 {

     Class<?> thisClass = (obj.getClass());

     String CLASS_NAME = thisClass.getSimpleName();

   

     String logFileName = "logs/" + CLASS_NAME + ".log";

   

     Properties props = new Properties();

     InputStream configStream = thisClass.getResourceAsStream("/log4j.properties");

     props.load(configStream);

     configStream.close();

   

     props.setProperty("log4j.appender.file.File", logFileName);

     LogManager.resetConfiguration();

    PropertyConfigurator.configure(props);

 }

 catch (Exception e)

 {

    e.printstacktrac();

 }

 }

Note: There are so many others ways also, however the above method is the simplest way to write logs into different files.