Discovering unused code in Java

When I set out to track down unused code in Java I came across a large number of static analysis tools that all seemed to do the job fairly well.

I used several of them including a fairly good eclipse plug-in called UCDetector. It was not fast, but it was very thorough.

By using those tools we were able to remove the obviously unused code. That resulted in a nontrivial shrinkage of about 30%. Unfortunately, due to the fact that much of the code gets called via Java's reflection API, There is a large amount of code that is not so obviously unused.

Since we have a UI test suite I thought that we would run the test suite against the front end and then log or track the methods that are actually called in the back end. Than we could eliminate the methods we found that were unused.

I first tried using the JDI interface of the JVM and simply remotely log each entrance into a method ( I didn't care about the exit). Unfortunately that slowed the Backend server system to a crawl. It would have taken weeks to get the data we needed.

I've tried both AspectJ and JBOSS AOP to produce a logging overlay and ran into significant problems deploying those in the older JBOSS 4.0.5GA environment. This was not significantly improved by the relatively nonstandard nature of our deployables.

Finally, we struck a gold mine. By using the YourKit profiler, which had minimal performance overhead, we were able to get the list of method calls that had been made. What made it especially easy was the profiler had a feature that would allow me to generate a dump of the call tree once an hour.

Here is the address of the profiler people: http://www.yourkit.com/

I just want to note that we were able to do all this using the evaluation version and that it easily passed a five minute test (. In other words, we were able to get it up and doing real work in five minutes). We have already ordered a copy.

Of course, taking 48 hours of those dumps and manually exporting them to CSV was a royal pain. To the YourKit guys: that is a hint.