Friday, May 29, 2009

Logging in Java

Yes, this is a very basic issue in Java programming, but sometimes it can be really confusing to find where the logs are and how to declaratively configure what to log.

Log4j is widely used and is configured using But some programmers choose to use Apache commons logging instead of using log4j API directly. Commons logging is a thin-wrapper for other pluggable logging tools, such log4j and Sun logging facility. The configuration guide of commons logging describes a five step procedure to find the underlying logging mechanism, among which, step 3 says:

"If the Log4J logging system is available in the application class path, use the corresponding wrapper class (Log4JLogger)."

In other words, usually even commons logging API is used in the program, the actual logging service is provided by log4j. Thus is used to configure how logging should be done.

Another logging configuration file is, which is used by java.util.logging.

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