SLF4J software introduction
slf4j, simple logging facade for Abbreviation for java, translated as java's simple log appearance. slf4j is an open source project that provides us with a consistent API to use different logging frameworks, such as: java.util.logging, logback, log4j, etc. slf4j enables users to embed the logging framework they want to use at runtime. As can be seen from the name, it is actually implemented using the facade design pattern.
When using slf4j, there is only one mandatory dependency, which is slf4j-api-x.x.x.jar. When we write code, we will only use the API in this jar package. The application will search the specific log framework bound in the class path at runtime, and use the bound log framework to perform actual log operations. If no suitable binding is found under the application's class path, slf4j will use an implementation without any operation by default.
slf4j is used in many famous projects, such as: Apache ActiveMQ, Ehcache, H2 database, Gradle, GreenMail, Hibernate.....
SLF4J software features
Binary compatible
An SLF4J binding specifies a specific dependency used to bind slf4j in the underlying logging framework, such as slf4j-jdk14.jar or slf4j-log4j12.jar.
Mixing different versions of slf4j-api.jar and SLF4J bindings may cause problems. For example, if you use slf4j-api-1.7.19.jar, then you should use slf4j-simple-1.7.19.jar, use slf4j-simple-1.5.5.jar will not work properly.
However, from a client perspective, all versions of slf4j-api are compatible. The client code compiled using slf4j-api-N.jar will be the same as slf4j-api-M.jar works perfectly together, N and M are both arbitrary. You just need to make sure that the version you bind matches slf4j-api.jar. You don’t need to worry about the dependencies given in your project Lai's version of slf4j-api.jar. You can use any version of slf4j-api.jar as long as As long as the version of slf4j-api.jar matches its binding, there will be no problem.
At initialization time, if SLF4J suspects there may be a mismatch problem. A warning message will be issued about the mismatch.
Unified logs through SLF4J
Often, a given project depends on a variety of components that rely on logging APIs other than SLF4J. It is common for a project to depend on a JCL, java.util.logging, log4j and SLF4J. Then it becomes satisfying to unify the logs in a single way. SLF4J provides support for JCL,
java.util.logging, and the slf4j bridging module to meet this common use case. For more details, please refer to Bridging legacy APIs.
MDC support
“Mapped Diagnostic "Context" is essentially a map included in the logging framework. The application code provides a key-value pair. This key-value pair can be inserted into the log information by the logging framework. MDC data is very useful when filtering information or triggering certain actions.
SLF4J supports MDC. If an underlying logging framework provides MDC functionality, SLF4J will delegate to the MDC of the underlying logging framework. Note that currently only log4j and logback provide MDC functionality. If the underlying logging framework does not support MDC, such as java.util.loggin, SLF4J will store the MDC number However, the data inside needs to be obtained by the user through code.
Therefore, as an SLF4J user, you can take advantage of MDC information when log4j and logback exist, but you cannot force the user to rely on these logging frameworks.
SLF4J usage instructions
1. If you use maven and add slf4j-api dependency, we use the latest version 2.0.0-alpha1; then add an implementation framework logback, logback-classic implements the slf4j interface, we also add the latest version 1.3.0-alpha5.
2. Add the logback.xml configuration file
3. Write a test program
SLF4J update log
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