编程语言java之log4j教程（国外英文资料）.docVIP

编程语言java之log4j教程（国外英文资料） Why not use system.out.println ()? Function is too weak; Its not easy to control. What if I dont want the output for the moment? What if you want to output to the file? What if you want partial output? ... Why use Commons - logging and Log4j at the same time? Why not just use one of them? The purpose of Commons - loggin is to provide a unified interface for all Java logging implementations, and its own logging capabilities are usually weak (there is only one simple SimpleLog?). So you dont normally use it alone. Log4j is a powerful and comprehensive feature that is currently preferred. I found that almost all of the Java open source projects use Log4j, but I also found that all projects that use Log4j often also use Commons - loggin. I think you dont want your project to be too close to Log4j binding. Another reason I can think of using Commons - logging and Log4j at the same time is to simplify usage and configuration. Emphasize that at the same time use the Commons - logging and Log4j, compared with single use Log4j, will not bring greater learning, configuration, and maintenance costs, but more simplify our work. I think thats one of the reasons why Commons - loggin is also used for all Log4j projects. What does Commons - logging do for us? L) provides a unified logging interface, simple operations, and avoids tight coupling between a project and a logging implementation system 2) its nice that we automatically select the appropriate logging implementation system (this is great!) 3) it doesnt even need to be configured Heres a look at how its very sweet to help us auto select the appropriate logging implementation system : 1) start by looking for your own configuration file Commons - logging. Properties under the classpath. If found, use the Log implementation class that is defined in it. 2) if you cant find a Commons - perties file, you are looking for a defined system environment variable mons. Logging. Log, find the Log implementation