JConsole
A graphical user interface monitoring tool for capturing information about performance, resource consumption of applications running on the Java platform.
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Reference: http://java.sun.com/javase/6/docs/technotes/guides/management/jconsole.html
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HOWTO: วิธีการตรวจสอบ memory leak ใน Java application
http://www.jhelp.net/article.aspx?id=10067
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Determining Memory Usage in Java
http://www.javaspecialists.eu/archive/Issue029.html