Version 0.3
Copyright © 2009 Lars Vogel
05.10.2009
| Revision History | ||
|---|---|---|
| Revision 0.1 | 01.10.2009 | Lars Vogel |
| Created | ||
| Revision 0.2 | 02.10.2009 | Lars Vogel |
| Example project | ||
| Revision 0.3 | 05.10.2009 | Lars Vogel |
| sub-chapters for example | ||
Table of Contents
The Java Garbage Collector releases Java objects from memory as long as no other object refers to this object.
A Java heap dump is an image of the complete Java object graph at a certain point in time. It includes all objects, Fields, Primitive types and object references.
It is possible to instruct the JVM to create automatically a heap dump in case of a OutOfMemoryError.
The Eclipse MAT helps to visualize based on Java heap dumps the references to objects and provides tools to identify potential memory leaks.
To tell the JVM to create a heapdump in case of an OutOfMemoryError use the option -XX:+HeapDumpOnOutOfMemoryError
Install Eclipse MAT via the update manager of eclipse (please see Eclipse Update manager for details). Select "General Purpose Tools " and install "Memory Analyser (Incubation)" and "Memory Analyser (Charts)".
Create the Java project "de.vogella.mat.first" and the package "de.vogella.mat.first". Create the following class.
package de.vogella.mat.first;
import java.util.ArrayList;
import java.util.List;
public class Main {
/**
* @param args
*/
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
while (1<2){
list.add("OutOfMemoryError soon");
}
}
}
In Eclipse add the -XX:+HeapDumpOnOutOfMemoryError to the runtime configuration.
Run the project.
You should get a new file in your project (.hprof). You may need to refresh your project (F5 on the project). Double-click it and select "Leak Suspects Report".
Switch back to the overview and start your analyses of the heap dump. I believe the user interface is quite intuitive. Expecially the dominator tree gives quickly an overview of the used objects.
You can also interactive create a HeapDump via the jconsole. Type jconsole in the the command line to start it.
To allow a Java program the access of jconsole use the -Dcom.sun.management.jmxremote start option.
Use them MBeans | com.sun.management | HotSpotDiagnostics | Operations |DumpHead .
More info can be found in JConsole and JConsole Tutorial .
Thank you for practicing with this tutorial.
I maintain this tutorial in my private time. If you like the information please help me by using flattr or donating or by|
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Before posting questions, please see the vogella FAQ . If you have questions or find an error in this article please use the www.vogella.de Google Group . I have created a short list how to create good questions which might also help you. .