Log level contstants was modified in LocationAwareLogger.java (see SLF4J-15). But jcl104-over-slf4j was not recompiled after that change. Because java compiler sometime puts constants into target method, there are sometime old values of these constants in jcl104-over-slf4j classes in http://www.slf4j.org/dist/slf4j-1.4.3.zip

For example, in class org.apache.commons.logging.impl.SLF4JLocationAwareLog there is following method:

public void warn(Object message)

{ logger.log(null, FQCN, LocationAwareLogger.WARN_INT, String.valueOf(message), null); }

In current class it is compiled as:

public void warn(Object message)

{ logger.log(null, FQCN, 2, String.valueOf(message), null); }

because 2 was old value of LocationAwareLogger.WARN_INT. It results in following exception:

java.lang.IllegalArgumentException: 2 not a valid level value
at ch.qos.logback.classic.Logger.log(Logger.java:820)
at org.apache.commons.logging.impl.SLF4JLocationAwareLog.warn(SLF4JLocat
ionAwareLog.java:141)

Perhaps all classes of sl4j needs recompilation.