Most modules use slf4j-logback. These don't and need to switch to that too:

jbpm-form-modeler-renderer: commons-logging (compile time even!)
jbpm-designer-backend: slf4j-jdk14 (compile time even!)
jbpm-designer-client: slf4j-jdk14 (compile time even!)
- Note: Many modules that depends on designer exclude logging dependencies because of this
jbpm-distribution: slf4j-log4j12
jbpm-examples: slf4j-log4j12
jbpm-executor: slf4j-log4j12
jbpm-test: slf4j-log4j12
droolsjbpm-bpms-distribution: slf4j-log4j12



HOW TO USE SLF4J AND LOGBACK PROPERLY
=====================================

Use slf4j with logback

Here's how it works:

1) In your java code, use the slf4 interfaces:
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;

Sfl4j is just a very-efficiently logging interface, it doesn't actually log itself.
Make sure you understand that
  logger.trace("Hello {}", username);
is a LOT faster than than
  logger.trace("Hello " + username);
if trace is disabled (which it usually is).

2) Add maven dependencies on slf4j-api and logback-classic:

    <!-- Logging -->
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
    </dependency>
    <dependency>
      <groupId>ch.qos.logback</groupId>
      <artifactId>logback-classic</artifactId>
      <scope>test</scope> <!--or <scope>runtime</scope> for examples and wars -->
    </dependency>

Remove/exclude any log4j and slf4j-log4j dependencies.
Note: log4j hasn't seen a release in 5 years. It's dead (and very slow).

3) Add a logback-test.xml file directly under in src/test/resources:
For example:
  https://github.com/droolsjbpm/optaplanner/blob/master/optaplanner-examples/src/test/resources/logback-test.xml

4) For end-user jars (so examples and wars, but NOT jbpm-flow etc), add a logback.xml directly under src/main/resources:
For example:
  https://github.com/droolsjbpm/optaplanner/blob/master/optaplanner-examples/src/main/resources/logback.xml

Note: If both logback-text.xml and logback.xml are on the classpath, logback will ignore the latter and only use logback-text.xml.
So never put logback-text.xml in a non-test classpath.

5) For more info:
http://www.slf4j.org/manual.html (how to use from code)
http://logback.qos.ch/documentation.html (how to configure it to do what you want it do)