Question

 java version '1.5.0_14' Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_14-b03) Java HotSpot(TM) Server VM (build 1.5.0_14-b03, mixed mode) 

I’m trying to debug a NullPointerException I’m getting for passing a reference to statically defined field. To be more specific, I’m setting a global on a Drools3 working memory instance.

workingMemory.setGlobal('log', workingMemorieslog); 

My assumption is that the Class where the field is statically defined is being garbage collected. (The receiving class must be using WeakReference or something like that, I don’t really know)

How would you suggest to debug this? I think that if I could know exactly when JVM’s GC unloads a class / instance of a class then I could narrow down on the cause of the buggy behavior. (If not the exact time of the event at least getting an indication that something did happened).

Thank you, Maxim.

Answer 1

To trace GC activity add this to java command:

-verbose:gc -XX:+PrintGCTimeStamps -XX:+PrintGCDetails

NPE that you are getting is probably you passing null value.