What Is Apache Log4j - A Logging Library for Java?

Apache Log4j is a reliable, fast and flexible logging framework written in Java.

With Log4j it is possible to enable logging at runtime without modifying the application binary. The Log4j package is designed so that these statements can remain in shipped code without incurring a heavy performance cost. Logging behavior can be controlled by editing a configuration file, without touching the application binary.

Logging equips the developer with detailed context for application failures. On the other hand, testing provides quality assurance and confidence in the application. Logging and testing should not be confused. They are complementary. When logging is wisely used, it can prove to be an essential tool.

One of the distinctive features of Log4j is the notion of inheritance in loggers. Using a logger hierarchy it is possible to control which log statements are output at arbitrarily fine granularity but also great ease. This helps to reduce the volume of logged output and the cost of logging.

The target of the log output can be a file, an OutputStream, a java.io.Writer, a remote Log4j server, a remote Unix Syslog daemon, or many other output targets.

Major versions of Apache Log4j:

               Version   JDK   Date 
               -------   ---   ----
Apache Log4j   2.14.1      8   2021-03-12
Apache Log4j   2.12.1      7   2020-07-03
Apache Log4j   2.3         6   2020-07-03
Apache Log4j   1.2.17    1.4   2012-05-06  
Apache Log4j   1.2.16    1.1   2013-02-01  
Apache Log4j   1.2.15    1.1   2007-08-30  
Apache Log4j   1.2.9     1.1   2005-06-23  
Apache Log4j   1.2.1     1.1   2004-04-19  
Apache Log4j   1.1.3     1.1   2004-04-19  
Apache Log4j   1.0.4     1.1   2004-04-19  

For more information, visit Apache Log4j Website.

⇒ Main Features of Apache Log4j

⇐ Introduction to Apache Log4j

⇑ Introduction to Apache Log4j

⇑⇑ FAQ for Apache Log4j