The open source log4j API for Java offers fast, efficient log services Summary Log4j, an open source project, allows developers to control which log statements are output with arbitrary granularity. It's fully configurable at runtime by using external configuration files. Best of all, log4j has a gentle learning curve.
Experience indicates that logging represents an important component of the development cycle.
As such, logging offers several advantages. First, it can provide precise context about a run of the application. Once inserted into the code, the generation of logging output requires no human intervention. Second, log output can be saved in a persistent medium to be studied at a later time. Finally, in addition to its use in the development cycle, a sufficiently rich logging package can also be employed as an audit tool.