How to detect the cause of OutofMemoryError?

Question

I have a complaint that a server application of mine is crashing on high load.
It is a web app running in Tomcat 5.
I see the thread dumps and I see that th

Answer 1

You should start the JVM with the -XX:+HeapDumpOnOutOfMemoryError flag. This will produce a heap dump when the OutOfMemoryError is generated.

Then, as @Steve said, you can use a tool like MAT to analyze the dump and see which objects are allocated, and who is keeping references to them. This usually will give you some insight on why your JVM is exhausting its memory.