SLF4J, Common Logging, console output

Question

I have this 3rd party library that has:

• slf4j-api-1.5.5.jar
• slf4j-jdk14-1.5.5.jar
• jcl-over-slf4j-1.5.5.jar

I want to write some tests against this library and see its log output, and I don't want to add any more logging libraries (no log4j or anything else).

I understand that SLF4J and Common Logging are both logging abstractions so I probably need to write my own simple concrete logger (or maybe not, since jcl-over-slf4j includes org.apache.commons.logging.impl.SimpleLog?). If so, what interfaces should I implement, and more importantly, how do I set up SL4J/Common Logging to use my logger in my test? I read in the SLF4J docs that I have to modify the StaticLoggerBinder class... does that really mean that I actually have to download SLF4J sources, modify the class and recompile it?

Answer 1

If you want to keep it simple, use the built-in (as of jdk 1.4) logger

https://docs.oracle.com/en/java/javase/19/docs/api/java.logging/java/util/logging/Logger.html

the jdk binding jar comes with slf4j. you want to make sure the jar is deployed to your webapp WEB-INF/lib dir or just in your classpath otherwise. See (slf4j.org/faq.html#where_is_binding) and this (slf4j.org/faq.html) for more information.

the jar you want to add to your classpath is slf4j-jdk14.jar. Note that the jdk logger is already available, this jar is the link between the slf4j interfaces and the chosen logger implementation. the jdk logging binding jar comes with the slf4j distribution. this should do it for you.

Answer 2

We use SLF4J. It's very useful but several of the jars have confusing names and it's not real clear starting out to know which ones are incompatible.

SLF4J is the API you use for logging in your code (e.g. log.info("blah"). However, SLF4J has no configuration aspect to it. At runtime you add exactly one jar to the classpath that binds the API to the 'real' logging subsystem. If you want to use Log4J, add slf4j-log4j.jar or the StaticBinder jar for Simple or JDK, or Logback. You configure any of these logging implementations as you normally would without SLF4J.

There are several SLF4J modules available to redirect existing logging statements written using the APIs of Log4J, Apache Commons Logging, and java.util.logging to SLF4J. This allows you to setup a single logging configuration for all these disperate implementations. (This is very useful to avoid configuring both, say, Log4J and JUL if you have libraries that bind directly to any legacy logging framework.)

The SLF4J legacy page explains these concepts in depth. Heck, there is even a module to redirect Sysout.out/err to SFL4J.

To more directly answer your question: sure you can write your own logging implementation to go under SLF4J; but the only reason to do so is because you are already locked into some homegrown craptastic logging framework.

Answer 3

Your question leds me to believe that you have not read the the SLF4J user manual. It's a very short document. If after reading the document you still have the same question, then the document fails its purpose and needs to be clarified.

Anyways, you don't need to implement your own Logger class. Just use slf4j-simple which ships with SLF4J.