LOG4J: Example

import com.foo.Bar;

 // Import log4j classes.
 import org.apache.log4j.Logger;
 import org.apache.log4j.BasicConfigurator;

 public class MyApp {

   // Define a static logger variable so that it references the
   // Logger instance named "MyApp".
   static Logger logger = Logger.getLogger(MyApp.class);

   public static void main(String[] args) {

     // Set up a simple configuration that logs on the console.

     logger.info("Entering application.");
     Bar bar = new Bar();
     logger.info("Exiting application.");

MyApp begins by importing log4j related classes. It then defines a static logger variable with the name MyApp which happens to be the fully qualified name of the class.

MyApp uses the Bar class defined in the package com.foo.

 package com.foo;
 import org.apache.log4j.Logger;

 public class Bar {
   static Logger logger = Logger.getLogger(Bar.class);

   public void doIt() {
     logger.debug("Did it again!");

The invocation of the BasicConfigurator.configure method creates a rather simple log4j setup. This method is hardwired to add to the root logger a ConsoleAppender. The output will be formatted using a PatternLayout set to the pattern “%-4r [%t] %-5p %c %x – %m%n”.

Note that by default, the root logger is assigned to Level.DEBUG.

The output of MyApp is:

0 [main] INFO MyApp – Entering application. 36 [main] DEBUG com.foo.Bar – Did it again! 51 [main] INFO MyApp – Exiting application.

The figure below depicts the object diagram of MyApp after just having called the BasicConfigurator.configure method.

Link: http://logging.apache.org/log4j/1.2/manual.html


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