Fast find memory leaks with Heap Analysis Tool

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Question: We have problem with memory leak in our java application. It seems that some objects do not become garbage collected.

We know that to be Garbage Collected an object must not be pointed by other one(s). Some object retention is still left. How can we find out which one does it?

Answer: It is not easy question to detect unnecessary object retention (or memory leaks).

It is true especially if an application has too many objects. Heap Analysis Tool could help. It is not included into 1.5 JDK because it is not a standard tool. The situation is changed with Java 6. It has been replaced with jhat.

HAT providing a convenient means to browse the object topology in a heap snapshot, which is generated by the Java VM. HAT reads a hprof file, then sets itself up as a web server--therefore allowing you to run queries against a heap dump contained within the hprof file. To generate a .hprof binary file, run java with the -Xrunhprof flag with "format=b" modifier:

java -Xrunhprof:file=dump.hprof,format=b MyClass

Since the Heap Analysis Tool is part of a research and development project, it is not an official product. Examples on exact HAT usage can be found at https://hat.dev.java.net/

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What do you not know about Java tools!

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Java Tools: Part 1.

Now days most of Java developers use different IDEs such as JIDEA, Eclipse or NetBeans to develop Java applications fast and easy. Used to work with rich graphical environment many developers have heard or read in readme.txt files from JDK that SUN provides "some" java tools. But since they are look boring - no nice GUIs and a lot of command line options - most of developers just miss them.

It is partly SUN's fault - the company does not do much to popularize those tools and provide very poor "dry" descriptions. We will try to repair this hole and publish reviews of Java tools and Utilities that could be useful for you. Today we will start with an overview of them.

All the Java tools can be divided into two groups:

• Standard, officially supported JDK Tools and
• Utilities and Unsupported, Experimental Ones

Standard JDK Tools and Utilities

• Basic Foundation Tools. They let you create and compile your applications, applets, docs, etc.
  javac, java, javadoc, apt, appletviewer, jar, jdb, javah, javap, extcheck
• Security Tools helps you to define, create and set security policies.
  keytool, jarsigner, policytool, kinit, klist, ktab
• Internationalization Tools will make work your applications abroad!
  native2ascii
• Remote Method Invocation (RMI) Tools With this tools you can make local applications remote and vice versa . Your applications will work over the Internet or other networks
  rmic, rmiregistry, rmid, serialver)
• Java IDL and RMI-IIOP Tools CORBA/IIOP, OMG-standard IDL with your applications
  tnameserv, idlj, orbd, servertool)
• Java Deployment Tools. Will help you to deploy your applets and applications everywhere on the Web
  pack200, unpack200
• Java Plug-in Tools Although names "tools" there is just one today which will plug in your applet to browsers
  htmlconverter
• Java Web Start Tools - although just one.. but reliably lunch your Java application
  javaws
• Java Monitoring and Management Console First in the raw graphical application for monitoring local and remote JVMs (by JMX) and applications
  jconsole

Experimental JDK Tools and Utilities

Since listed below tools are unsupported and experimental they might not be available in future JDK versions.

• Monitoring Tools Performance statistics (JVM monitoring)
  jps, jstat, jstatd
• Troubleshooting Tools If you in big or even small troubles this helpful bunch of tools will save your career!
  jinfo, jhat, jmap, jsadebugd, jstack
• Scripting Tools Since the name JavaScript is already taken by another guys, it is written just: Script shell for Java - Runs a script. Probably Java script, not JavaScript
  (jrunscript)

In our next articles every java tool will be described with examples and explanation how they can increase efficiency of your daily work.

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