In this last article of the series I'll show how to use the native JMX support within the JDK to implement a notification mechanism which alerts a listener when the HEAP memory is above a certain threshold.

As discussed in my previous article this approach is ideal because is push instead of pull, is not intrusive and places minimal computing demand on your application.

These are the key components to the solution illustrated in this article:

• MemoryWarningService: This component acts as a listener and registers itself with the Memory MBean to receive notifications. It is configurable with a threshold in the form of a percentage between 0 and 1 (where 1 is 100%)
• MemoryThreadDumper: This component is invoked when the MemoryWarningService is notified that the HEAP usage is above the threshold and its responsibility is to write a thread dump to a file
• MemoryWarningServiceConfigurator: This component is an MBean and exposes a method to change the threshold of the MemoryWarningService.

The solution provides also a MemoryHeapFiller class used to fill up the HEAP while testing the application and a MemTest class to bootstrap the Spring environment.

While the application is running (play with the MemoryHeapFiller settings) You can fire the JConsole at URL: service:jmx:rmi://localhost/jndi/rmi://localhost:8888/jemosJmxConnector connecting as jemosAdmin / secure and change the threshold to various values.

The code is not meant for production: it is not robust, there are numerous comments missing, and the filename where to write the thread dump is hard-coded; it represents, however, a good starting point.

The code is attached below. You will need Maven to build it.

Download Jemos-jmx-experiments-0.0.1-SNAPSHOT-project

I tried a scenario with initial threshold to be 0.5, I changed it to 0.3 and then to 0.8. The results are shown below:

2011-08-15 21:53:21 ClassPathXmlApplicationContext [INFO] Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@a4a63d8: startup date [Mon Aug 15 21:53:21 BST 2011]; root of context hierarchy
2011-08-15 21:53:21 XmlBeanDefinitionReader [INFO] Loading XML bean definitions from class path resource [jemos-jmx-appCtx.xml]
2011-08-15 21:53:21 PropertyPlaceholderConfigurer [INFO] Loading properties file from class path resource [jemos-jmx.properties]
2011-08-15 21:53:21 PropertyPlaceholderConfigurer [INFO] Loading properties file from URL [file:/C:/Users/mtedone/.secure/jmxconnector-credentials.properties]
2011-08-15 21:53:21 ThreadPoolTaskScheduler [INFO] Initializing ExecutorService  'myScheduler'
2011-08-15 21:53:21 ClassPathXmlApplicationContext [INFO] Bean 'myScheduler' of type [class org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2011-08-15 21:53:21 DefaultListableBeanFactory [INFO] Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@30296f76: defining beans [propertyConfigurer,loggerConfigurator,memoryWarningServiceConfigurator,memoryHeapFiller,memoryThreadDumper,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,mbeanExporter,jemosJmxServer,rmiRegistry,clientConnector,memoryMxBean,memoryWarningService,org.springframework.scheduling.annotation.internalAsyncAnnotationProcessor,org.springframework.scheduling.annotation.internalScheduledAnnotationProcessor,myScheduler]; root of factory hierarchy
2011-08-15 21:53:21 AnnotationMBeanExporter [INFO] Registering beans for JMX exposure on startup
2011-08-15 21:53:21 RmiRegistryFactoryBean [INFO] Looking for RMI registry at port '8888'
2011-08-15 21:53:23 RmiRegistryFactoryBean [INFO] Could not detect RMI registry - creating new one
2011-08-15 21:53:23 ConnectorServerFactoryBean [INFO] JMX connector server started: javax.management.remote.rmi.RMIConnectorServer@4355d3a3
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Bean with name 'jemosJmxServer' has been autodetected for JMX exposure
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Bean with name 'loggerConfigurator' has been autodetected for JMX exposure
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Bean with name 'memoryWarningServiceConfigurator' has been autodetected for JMX exposure
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Located managed bean 'loggerConfigurator': registering with JMX server as MBean [jemos.mbeans:type=config,name=LoggingConfiguration]
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Located MBean 'jemosJmxServer': registering with JMX server as MBean [jemos.mbeans:name=jemosJmxServer,type=RMIConnectorServer]
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Located managed bean 'memoryWarningServiceConfigurator': registering with JMX server as MBean [jemos.mbeans:type=config,name=MemoryWarningServiceConfiguration]
2011-08-15 21:53:23 MemoryWarningService [INFO] Percentage is: 0.5
2011-08-15 21:53:23 MemoryWarningService [INFO] Listener added to JMX bean
Adding data...
Adding data...
Adding data...
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Adding data...
Adding data...
Adding data...
2011-08-15 21:53:37 MemoryWarningService [INFO] Percentage is: 0.3
2011-08-15 21:53:37 MemoryWarningServiceConfigurator [INFO] Memory threshold set to 0.3
Adding data...
2011-08-15 21:53:38 MemoryWarningService [WARN] Memory usage low!!!
2011-08-15 21:53:38 MemoryWarningService [WARN] percentageUsed = 0.3815679398794023
2011-08-15 21:53:38 MemoryThreadDumper [WARN] Stacks dumped to: C:/tmp/stacks.dump
Adding data...
Adding data...
Adding data...
2011-08-15 21:53:45 MemoryWarningService [INFO] Percentage is: 0.8
2011-08-15 21:53:45 MemoryWarningServiceConfigurator [INFO] Memory threshold set to 0.8
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
2011-08-15 21:54:01 MemoryWarningService [WARN] Memory usage low!!!
2011-08-15 21:54:01 MemoryWarningService [WARN] percentageUsed = 0.8383333266727508
2011-08-15 21:54:02 MemoryThreadDumper [WARN] Stacks dumped to: C:/tmp/stacks.dump
Adding data...
Adding data...
Adding data...
Exception in thread "JMX server connection timeout 24" java.lang.OutOfMemoryError: Java heap space

Happy technology!

From http://tedone.typepad.com/blog/2011/08/jmx-and-spring-part-3.html