Log4j是Apache的一个开放源代码项目，通过使用Log4j，我们可以控制日志信息输送的目的地是控制台、文件、GUI组件，甚至是套接口服务器、NT的事件记录器、UNIX Syslog守护进程等;我们也可以控制每一条日志的输出格式;通过定义每一条日志信息的级别，我们能够更加细致地控制日志的生成过程。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 an open source project Apache, by using Log4j, we can control the log information delivery destination file, console, GUI components, and even set interface server, NT, UNIX Syslog event logger daemon; we can also control the output format of each log by defining each; a log information level, we can generate a more detailed process control log. Most interesting is that these can be configured flexibly through a configuration file without the need to modify the code for the application.)