A profiler is a development tool that lets you examine memory useage and other bottlenecks in your app.
I've tried some of them.
For the big problems jprofiler is great. The docs are useful, the interface is good and the performance is okay. I prefer jMechanic. It's small, free and works together with WOLips. Just some clicks to set it up.
I don't remember much about the others. Some of them don't run under MacOSX and it can take a lot of time to find how to use them together with WO.
profiler homepage: http://www.ej-technologies.com/products/jprofiler/overview.html j jmechanic homepage: http://sourceforge.net/projects/jmechanic/ to see jmechanic in action click on the profiler link: http://objectstyle.org/woproject/gallery.html Ulrich
If profiling on Windows is an option, you might also want to look at jSprint: http://www.javaperformancetuning.com/tools/jsprint/index.shtml
It is shareware, US$50. I've used it and was satisfied with it. It seems like a good deal for the price. I've not (yet) used jMechanic, so I can't compare the two.
Before you buy anything or try anything you would be well advised to spend a couple of hours at the above Java Performance Tuning site reading up on it: http://www.javaperformancetuning.com/index.shtml There is a lot of good information there.
(As of March 2007 the J-Sprint link above does not seem to work - the software may not be available anymore) None of the tools on this page appear to work with WebObjects 4.5.1 on Windows.
I use JProfiler from ej-technologies. It works as well as any of the other big named profilers, and it has explicit support for WebObjects. It is, however, not free like some of the other suggestions.
Pierce T. Wetter IIIEdit
The CHUD tools (i.e. Shark) work on Java.