The relationship between the Java log commons-logging log4j slf4j

One, before the log operation is generally in a class to add the following code:

Import org.apache.log4j.logger;//introduced the LOG4J package private static final Logger LOG = Logger.getlogger (Test.class);

Second, later saw someone else's code is written like this:

Import Org.apache.commons.logging.log;import org.apache.commons.logging.logfactory;// Introduced is the commons-logging package private static Log logger = Logfactory.getlog (Accountaction.class);

Third, later think of using log4j to put MyBatis SQL statement output also need to add Slf4j-api-x.x.x.jar and Slf4j-log4j12-x.x.x.jar two packets. See so many logs, messy, so on the degree of Niang, a little understanding of the relationship between these logs. Here by the way to give a more superficial summary, crossing have a better understanding can leave a message, we learn progress together.

1) commons-logging and Slf4j-api

Both of these log packages provide a standard interface. Similar to JDBC, give an interface, specifically how to implement your own to play. The difference is that commons-logging itself has a simple implementation. Therefore, in the (b) code, if the introduction of commons-logging does not introduce log4j of the rack package, the log can print normally, the printing effect is as follows:

If you join LOG4J's rack package (you need to configure Log4j.properties or log4j.xml), the log effect is as follows:

In simple terms, Commons-logging will go to find the commons-logging.properties configuration file, look for the specified implementation log, if not, the default to find Log4j (after all, it is home-made things), if not specified, and did not find the log4j rack package implementation, then, Commo Ns-logging on their own, the result is a picture of the effect. There is no default implementation of SLF4J.

2, Slf4j-api and SLF4J-LOG4J12

There must be inconsistencies between the interfaces of Slf4j-api and commons-logging. Some log implementations may not follow the Slf4j-api interface, so the intermediate conversion is one layer. So Slf4j-log4j12 is a taste similar to a converter. Log4j is used after the conversion. Of course there are others, such as Sli4j-slf4j-logback.

Iv. Summary

1) The use of their own projects to introduce Commons-logging and log4j two rack package, and then use (ii) in the Code;

2) Some projects may be used slf4j, such as MyBatis, if you want to continue to use log4j need to introduce slf4j-log4j12;

3) The use of log4j two combinations: "commons-logging+log4j" and "slf4j+slf4j-log4j12+log4j";

This article is for log4j only, and other open source logs are not covered. Rookie's opinion, Daniel do not spray.

The relationship between the Java log commons-logging log4j slf4j