content/markdown/maven-logging.md

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# Maven 3.1.x logging

Maven 2.x and 3.0.x use [Plexus logging API][6] with basic Maven implementation writing
to stdout.

We have reached the decision that [SLF4J][1] is the best option for a logging API:
SLF4J has reached a certain level of ubiquity and while SLF4J may not be perfect,
it\'s the de facto standard and it\'s pointless to try and remake another one.
There are many implementations to choose from, including [Logback][4] and [Log4j2][3].
All the hard work has been done. All the bridges and funnels for other systems function well,
which allows others to use whatever logging implementation they like in their components,
while still being able to have integrated logging.

The standard Maven distribution, from Maven 3.1.0 onward, uses the [SLF4J API][5] for logging
combined with the [SLF4J Simple][2] implementation. Future versions may use a more advanced
implementation, but we chose to start simple.

Looking at the distribution you will
see the following layout where the `simplelogger.properties`, `slf4j-api-x.y.z-jar` and
`slf4j-simple-x.y.z.jar` specifically relate to the SLF4J implementation:

<div class="source"><pre>
apache-maven-3.x.y
├── LICENSE.txt
├── NOTICE.txt
├── README.txt
├── bin
│   └── ...
├── boot
│   └── ...
├── conf
│   ├── logging
│   │   └── simplelogger.properties
│   └── settings.xml
└── lib
    ├── ...
    ├── slf4j-api-x.y.z.jar
    ├── slf4j-simple-x.y.z.jar
    └── ...
</pre></div>

## Configuring logging 

To configure logging with the [SLF4J Simple][2], you can edit the properties in the
`${maven.home}/conf/logging/simplelogger.properties` file. Please see the linked reference documentation
for details.

Every entry in this file can be overriden via commandline arguments by passing it with the `-D` flag. 
E.g. `-Dorg.slf4j.simpleLogger.showThreadName=true` will add the thread name to every logging line.

The default configuration for Maven is listed [here][8].

## Changing the SLF4J implementation

If you want use a different logging implementation it is simply a matter of removing the slf4j-simple JAR
from the `lib` directory and replacing it with one of the alternative implementations, like [Log4j2][3] or [Logback][4].

See SLF4J documentation for more details on [swapping "SLF4J bindings"][7]. 

[1]: http://slf4j.org
[2]: http://www.slf4j.org/apidocs/org/slf4j/impl/SimpleLogger.html
[3]: https://logging.apache.org/log4j/2.x/log4j-slf4j-impl/
[4]: http://logback.qos.ch
[5]: http://slf4j.org/apidocs/
[6]: https://codehaus-plexus.github.io/plexus-containers/plexus-container-default/apidocs/org/codehaus/plexus/logging/package-summary.html
[7]: http://www.slf4j.org/manual.html#swapping
[8]: https://git-wip-us.apache.org/repos/asf?p=maven.git;a=blob;f=apache-maven/src/conf/logging/simplelogger.properties;h=eb3d0496d2817cb254d961e788c9847eb1a7d45b;hb=HEAD