Catching java.lang.OutOfMemoryError?

Question

Documentation for java.lang.Error says:

An Error is a subclass of Throwable that indicates serious problems that a reasonable application

Answer 1

Yes, the real question is "what are you going to do in the exception handler?" For almost anything useful, you'll allocate more memory. If you'd like to do some diagnostic work when an OutOfMemoryError occurs, you can use the -XX:OnOutOfMemoryError= hook supplied by the HotSpot VM. It will execute your command(s) when an OutOfMemoryError occurs, and you can do something useful outside of Java's heap. You really want to keep the application from running out of memory in the first place, so figuring out why it happens is the first step. Then you can increase the heap size of the MaxPermSize as appropriate. Here are some other useful HotSpot hooks:

-XX:+PrintCommandLineFlags
-XX:+PrintConcurrentLocks
-XX:+PrintClassHistogram

See the full list here