How to determine where an object was instantiated in VisualVM Heap Dump

Question

I have a bug in my program that is generating a lot of String instances (7000+ in Heap according to VisualVM ). I am trying to isolate which class is responsible for this so I can understand why it is happening.

The following is an example of the heap dump for String :

How do I figure out which class is responsible for generating each of the String ? I am working with about 40 classes together so I would like to be able to identify the culprit class through VisualVM if possible.

Answer 1

You should have a look at this Q/A: How to view memory allocation stacktrace in Java VisualVM - a heap profile, which is a "memory allocation stacktrace" is what you want.

Here is a nice tutorial : Analyzing Memory Leak in Java Applications using VisualVM .

In general, there is several ways howto diagnose this problem, using a Java profiler:

• use CPU profiling , the best in a instrumentation mode, this will record all method invocations, look at String.<init> - this will show you all the possible methods that execute new String() . The best tools are eg jProfiler, Java Mission Control, where you can easily identify all the callers of the String.<init> . The same applies for VisualVM. I think using CPU profiling is the most straightforward way of idenifying where in the code the new String occurs the most.

• collect a heap dump in MAT , and analyze that, this will allow you to traverse the heap, you will again search for String finding all the references to a String object.

• use Heap profiling option of a Java profiler (eg VisualVM), is similar to collecting a heap dump, only this heap profiling is usually collected online. So just enable heap profiling in VisualVM and follow the references from the String instances (ie find objects referencing String).