Log4j Hello World Program

Let us see one simple program in Log4j

For working with log4j, we must set log4j.jar in our class path

Files Required

• Client.java
• my.txt   [ We will let the appender to write into this file ]

Directory Structure

Client.java

import org.apache.log4j.Appender;
import org.apache.log4j.FileAppender;
import org.apache.log4j.Layout;
import org.apache.log4j.Logger;
import org.apache.log4j.SimpleLayout;

public class Client {

  static Logger l = Logger.getLogger(Client.class.getName());

  public static void main(String[] args) {	  

	  Layout l1 = new SimpleLayout();
	  Appender a;
	  //Appender a = new ConsoleAppender(l1);
	  try
	  {
	  a = new FileAppender(l1,"my.txt", false);

	  // 3rd parameter is true by default
	  // true = Appends the data into my.txt
	  // false = delete previous data and re-write

	  l.addAppender(a);
	  }
	  catch(Exception e) {}	  

	  l.fatal("This is the error message..");
	  System.out.println("Your logic executed successfully....");
  }
}

Once we run this client program, my.txt will contains….

my.txt

FATAL – This is the error message..

Explanation

• First step is to create one Logger class object [ see line number 9 ]
• Second step is to create Layout object  [ see line number 13 ]
• Once Layout is ready, our next step is to create Appender [ see line number 18 ]
• In appender i have passed 3 parameters like.. first parameter is object of layout because, appender will write the error messages based on the layout we selected, then 2nd parameter is file name with extension [ in this file only appender will writes the messages ], then 3rd parameter is by default true, means appender will appends the error messages, if we give false then appender will clears the previous data in my.txt file and write newly

Hey see, i have used FileAppender, but if i would like to change my appender choice to ConsoleAppender, then again we must open this java file then modifications and recompile bla bla…, so to avoid this we can use one .properties file, will see this in the next session.

What you are thinkig....