Log4J是Apache软件基金会Jakarta项目下的一个子项目，是用Java编写的优秀日志工具包。通过Log4J可以在不修改代码的情况下，方便、灵活地控制任意粒度的日志信息的开启或关闭，然后使用定制的格式，把日志信息输出到一个或多个需要的地方。

最令人感兴趣的就 是，这些可以通过一个配置文件来灵活地进行配置，而不需要修改应用的代码。

-Log4J is the Apache Software Foundation Jakarta under a subproject is prepared to use Java logging toolkit outstanding. Log4J can be adopted without amending the code, the convenience, flexibility to control arbitrary granularity of the log information of the open or closed, then use the custom format, the log information output to one or more needed. Most interesting is that these can be through a configuration file to configure a flexible manner, without modifying application code.