[slf4j-user] Question regarding slf4j and 3rd parties libraries

[Joern Huxhorn]

Hi Olivier.

On 25.05.2010, at 10:53, Olivier Bourdon wrote:

> Hello everyone
> 
> let's assume that my Java code is using several different 3rd parties libraries (Hibernate, Jersey and some others) which
> use "potentially unknown" logging mechanisms (java standard logging or log4j). How will slf4j behave in this case as
> I know I can not use more than 1 binding ? Do I need any special configuration file settings ?
> 

You'd use one binding - I'd suggest Logback - and bridge all other logging frameworks to SLF4J.

I can only explain a bit for maven.

In the 3rd-party dependency that is using one of the bridged frameworks, exclude it in your pom file, e.g. like this:
<dependency>
	<groupId>commons-cli</groupId>
	<artifactId>commons-cli</artifactId>
	<version>1.2</version>
	<exclusions>
		<exclusion>
			<groupId>commons-logging</groupId>
			<artifactId>commons-logging</artifactId>
		</exclusion>
	</exclusions>
</dependency>

You can do so either in the pom of your application or in the <dependencyManagement>-part of your parent pom.

Doing just this would result in a ClassNotFoundException during runtime so you have to add the bridging jar manually to your application. For commons-logging, this is:
<dependency>
	<groupId>org.slf4j</groupId>
	<artifactId>jcl-over-slf4j</artifactId>
	<version>${slf4jVersion}</version>
</dependency>

You need to check all dependencies of your application for left-over dependencies, though, so no dependency is still including commons-logging.

mvn dependency:tree

is incredibly helpful concerning this.

Do the same for any log4j-dependency and use 
<dependency>
	<groupId>org.slf4j</groupId>
	<artifactId>log4j-over-slf4j</artifactId>
	<version>${slf4jVersion}</version>
</dependency>
instead.

Bridging jul to SLF4J is a bit more complex since the original implementation can't be swapped out since they are contained in the java-package.

Take a look at http://www.slf4j.org/legacy.html

<shameless-plug>
And while you get happy with SLF4J and Logback, be sure to take a look at Lilith, too.
http://lilith.huxhorn.de
</shameless-plug>

Cheers,
Joern.