Log4j is implementation of commons-logging or slf4

问题:

Hy,

I have read that commons-logging and slf4j are "interfaces or specifications" for logging and you have to plugin an implementation. But I have read that you can use log4j for example with commons-logging and with slf4j too, so: log4j "implements" the specifications of commons-logging and slf4j at the same time? I dont understand it

Thanks

回答1:

SLF4j is a logging facade and can be introduced into both Log4j and commons-logging projects. So you use SLF4j classes to perform the logging it just acts like a facade. Underneath, you can have either Log4j or any other logging system that is supported by SLF4j. The advantage by doing so is that SLF4j relives you from getting tied to a specific logging system.

回答2:

Sl4j and commons-logging are both facades for underlying logging implementations such as log4j or JDK logging. They work by having their own logging interface, whith multiple implementations, each implementation wrapping the logger interface of the concrete logging framework. So, in the log4j example, Slf4j's org.slf4j.Logger interface has an implementation which wraps a Log4j org.apache.log4j.Logger, not the other way around. The same mechanism applies with commons-logging. This enables using Log4j standalone, with Slf4j or with commons-logging, as you wish.