Damn Log4j

While debugging a problem, I was annoyed to find that the logs just contained the name of the exception and not the stack trace. The code in question was essentially:

try {
    doSomething();
} catch (Throwable t) {
    _logger.warn(t);
}

The problem is that the Logger.warn(Object) method of log4j accepts an object and not a string so the code compiles without issue. The correct method for exceptions is Logger.warn(Object,Throwable). Having a method in java that accepts a parameter of type Object should be done with caution as anything (even primitive types due to autoboxing) can be passed in with no compile time validation. Curious, I decided to look at what other logging libraries chose to do.

• java.util.logging.Logger: uses a string for the message.
• org.apache.commons.logging.Log: uses an object for the message.
• org.slf4j.Logger: uses a string for the message.