What Good Is JMX?

JMX exposes JVM Garbage Collection and other metrics from JConsole or as a remote JMX client.

JMX can also be used by programmers to signal application-specific counts and timings such as how long back-end database requests took to process.

Getting Started With JMX

Sun's Reference implementation of JMX is the most "authoritative".

• JMX 1.1 (Sun JSR 3) Spec, Download

• JMX 1.2 (Sun JSR 3) Spec, Download

• JMX 1.2.1 (Sun JSR 3) 2003Aug22 Download

• JMX 1.2 extended to remove JMX Mbean servers. JMX Remote API 1.0 (Sun JSR 160) Spec, Download

Other reference implementations are more complete:

• Sun's Java Dynamic Management Kit (JDMK) 5.1 (90 demo) commercializes JMX.
• IBM Tivoli's JMX implementation
• AdventNet Agent Toolkit JMX Edition

JMX Components

1. Mbeans (at the Instrumentation level) collect information in manageable units.
2. A registry of MBeans is maintained at the Agent level where an MBean server (examples/BaseAgent/) runs within a Java Virtual Machine (JVM). The MBean server provide a communications link between MBeans and the remote management applications that reside on the management client. Standard agent services include a timer scheduler and event-notifier service, Mbean attribute monitoring service, m-let dynamic loading service, and relation service to maintain relationships among MBeans. All these are implemented as MBeans.
3. At the Manager level, connectors are used by the MBean Server to communicate with a systems management application that runs on a management client. Protocol adapters for HTML, XML, etc. are used to communicate with web browsers and other clients.

Types of Mbeans

Message MBeans differ in the way they expose the management interface of the application resource to the agent.

• Standard MBeans define the management interface of the application resource as a Java interface. Standard MBeans manages resources whose structure do not change over time.
• Dynamic MBeans implement the JMX DynamicMBean interface. A JMX agent constructs the metadata of the resource represented by Dynamic MBean at runtime using the methods of this interface.
• Model MBeans implement the JMX ModelMBean interface which extends the DynamicMBean interface. Model MBeans use descriptor objects to include MBean behavior characteristics, such as persistence and caching.
• Open MBeans are defined in the JMX specification as optional. Open Mbeans are a special type of Dynamic MBeans that use only pre-defined data types in their definition, so they have limited class loading at runtime.

Monitor MBeans report attributes when values change.

Reference Implementation Java Library

lib/jmxri.jar (JMX reference implementation Java class package) and
lib/jmxtools.jar (JMX toolkit)
should be added to the Java SDK 2 OS CLASSPATH environment variable.

Package	Class	Description
javax.management	Core classes
javax.management.loading	-
javax.management.monitor	listener mechanism for receiving its notifications
javax.management.timer	-
javax.management.relation	handles relations, relation types and to perform queries to retrieve relations.
javax.management.modelmbean	-
javax.management.openmbean	-
javax.management.mbeanserver		?
javax.management.notification		?
javax.management.mlet		?
com.sun.jmx.*	-
com.sun.management.jmx	-
com.sun.jdmk.*	-

BaseAgent

Instructions for compiling and running MBeanServer on Windows:

@REM Run from within the examples folder:
mkdir tutorial

@REM Compile the BaseAgent class in this new directory with all the example classes:
copy BaseAgent/BaseAgent.java tutorial
copy MonitorMBean/Simple.java tutorial
copy MonitorMBean/SimpleMBean.java tutorial
copy DynamicMBean/SimpleDynamic.java tutorial
cd tutorial
dir tutorial
javac *.java
cd ..
java tutorial/BaseAgent
pause

Closing the window shuts down the service.

Seeing "Adaptor:name=html,port=8082" means you can get the Agent View at http://localhost:8082/

Click the "Admin" button for the Agent Admin view.

Your Own MBean

Creating and registering a standard MBean involves:

1. Defining the management interface.
2. Defining the standard MBean that will implement the management interface.
3. Instantiating the JMX agent.
4. Registering the MBean with the JMX agent so that it can be accessed remotely.