Making simple performance modifications to an already compiled jar?

Question

Like many log4j users, we often have debug level logging that is expensive to evaluate. So we guard those cases with code like:

if( _logger.isDebugEnabled )
  _logger.debug("Interesting, my foojes are goofed up: " + getFullDetails())

However, that is uglier than a plain _logger.debug call, and sometimes the programmer doesn't realize the evaluation could be expensive.

It seems like it should be fairly simple to write a program that takes a compiled jar and guards all the _logger.debug calls with the isDebugEnabled check. We would likely be willing to accept the extra overhead of checking isDebugEnabled in all cases.

Has anyone tried this approach, or done similar post-processing of a jar?

Answer 1

Rather than looking at modifying the jar, I'd search for a solution using Bytecode Instrumentation. The problem will be to identify those parts of the code you want to wrap inside a .isDebugEnabled() - you will have to identify objects that are only used for log4j invocations.

Answer 2

Have you looked at AspectJ ? This supports aspects using bytecode weaving, and can interceptions into a previously compiled .jar file.