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Java Platform, Standard Edition Troubleshooting Guide
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2.9 JConsole

Another useful tool included in the JDK download is the JConsole monitoring tool. This tool is compliant with JMX. The tool uses the built-in JMX instrumentation in the JVM to provide information about the performance and resource consumption of running applications. Although the tool is included in the JDK download, it can also be used to monitor and manage applications deployed with the JRE.

The JConsole tool can attach to any Java application in order to display useful information such as thread usage, memory consumption, and details about class loading, runtime compilation, and the operating system.

This output helps with high-level diagnosis of problems such as memory leaks, excessive class loading, and running threads. It can also be useful for tuning and heap sizing.

In addition to monitoring, JConsole can be used to dynamically change several parameters in the running system. For example, the setting of the -verbose:gc option can be changed so that garbage collection trace output can be dynamically enabled or disabled for a running application.

For more details, see the jconsole command man page. For FAQs, see JConsole and Remote Management of Java Platform.

The following sections describe troubleshooting techniques with JConsole tool.

2.9.1 Troubleshoot with JConsole Tool

The following list provides an idea of the data that can be monitored using the JConsole tool. Each heading corresponds to a tab pane in the tool. For details on how to use JConsole tool, see Using JConsole.

2.9.2 Monitor Local and Remote Applications with JConsole

JConsole can monitor both local applications and remote applications. If you start the tool with an argument specifying a JMX agent to connect to, then the tool will automatically start monitoring the specified application.

To monitor a local application, execute the command jconsole pid, where pid is the process ID of the application.

To monitor a remote application, execute the command jconsole hostname:portnumber, where hostname is the name of the host running the application, and portnumber is the port number you specified when you enabled the JMX agent.

If you execute the jconsole command without arguments, the tool will start by displaying the New Connection window, where you specify the local or remote process to be monitored. You can connect to a different host at any time by using the Connection menu.

With the latest JDK releases, no option is necessary when starting the application to be monitored.

As an example of the output of the monitoring tool, Figure 2-15 shows a chart of heap memory usage.

For more details on the monitoring and management capabilities, and how to use jconsole, see the Java SE Monitoring and Management Guide.

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