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Please, is there any way how to get history of objects (their variable or at least class names) that have been garbage collected in Java?

Just adding these params (to Oracle JVM)

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

doesn't provide anything else memory in bytes. It's very limited help to me. Thanks for all responses.

Note: Workaround with add finilize() method is not unfortunatelly an option for me (I don't have an access to it).

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5 Answers 5

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You can use the finalize method from Object. This method is called when the object is about to be GCed. From here, you can log the information you need.

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Disclaimer: My company develops the tool that I recommend in this answer.

In JProfiler you can go to the "Recorded objects" view in the memory section and switch the liveness mode to garbage collected objects (View->Change Liveness Mode->Garbage Collected Objects). You will then see a statistics of objects that have been GCed.

enter image description here

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Thanks. JProfiler looks awesome but 450€ is too very expensive
Is there any way to list down the classes programmatically? I was going through the java.lang.Management package but it can return count only.
You mean in JProfiler or in a JDK MBean?
How do I record memory from JVM start? - The UI forces me to click on a button - but my program runs only for 5 seconds
@Hurda In the dialog that is shown when you start a profiling session, you can configure an initial recording profile.
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Are you searching for a memory leak?

If you implement finalize() method (available in every Object) it will get called just before the object is being garbage collected - and you can run any code inside it.

If you are looking for a systematic solution (or you don't have access to classes you want to monitor), I am not aware of any JVM option that allows that. However you can log classes being loaded and unloaded (GCed), but this is not what you are asking.

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Weak references or phantom references seem to be useful to log when the object actually gets removed. In this article the technology is explained.

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There is a nice built-in tool in JDK for observing jvm in runtime. It is jvisualvm. There is a a good reference with screenshots: http://visualvm.java.net/description.html

Here is one of them : enter image description here

Hope that helps.

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jprofiler is a very powerful and common used tool but it is free only for opensource and the standard license for single instance costs real money - $500. It might be a problem for some projects.
I know and using VisualVM but it doesn't support to see garbage collected objects.
That is a useful tool, but it doesn't answer this particular need.

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