Getting Started with Java Management Extensions (JMX): Developing Management and Monitoring Solutions
By Qusay H. Mahmoud, January 6, 2004
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The Java Management Extensions (JMX) API is a standard specification—developed through the Java Community Process (JCP) as JSR 3—for managing and monitoring applications and services. It defines a management architecture, design patterns, APIs, and services for building Web-based, distributed, dynamic, and modular solutions to manage Java-enabled resources. The JMX APIs make it possible to add manageability to Java-enabled equipment, from web phones to set-top boxes to network devices and servers. Using JMX technology to manage applications and services increases their value to vendors and clients by making applications easier to install, configure, and maintain.
This article provides a fast track technical tutorial to JMX. It discusses JMX and its tiered architecture, the JMX programming model, and code demonstrating how to use JMX to develop management applications. In addition, the article shows how to use a JMX-compliant management tool in the Java 2 Platform, Standard Edition 5.0 (J2SE 5.0), which has implemented version 1.2 of the JMX specification.
Overview of JMX
JMX is native to the Java programming language. As a result, it offers natural, efficient, and lightweight management extensions to Java-based functions. It consists of a set of specifications and development tools for managing Java environments and developing state-of-the-art management solutions for applications and services. It provides Java developers with the means to instrument Java code, create smart Java agents, implement distributed management middleware and managers, and easily integrate these solutions into existing management and monitoring systems. The dynamics of JMX enable you to use it to monitor and manage resources as they are implemented and installed. It can also be used to monitor and manage the Java Virtual Machine (JVM machine).
Typical uses of the JMX technology include:
Consulting and changing application configuration
Collecting statistics about application behavior and making the statistics available
Notification of state changes and erroneous conditions
Benefits of JMX
The JMX technology enables Java developers to encapsulate resources as Java objects and expose them as management resources in a distributed environment. The JMX specification lists the following benefits to using JMX to build a management infrastructure:
Manages Java applications and services without heavy investment: JMX architecture relies on a core managed object server that acts as a management agent and can run on most Java-enabled devices. Java applications can be managed with little impact on their design.
Provides a scalable management architecture: A JMX agent service is independent and can be plugged into the management agent. The component-based approach enables JMX solutions to scale from small footprint devices to large telecommunications switches.
Can leverage future management concepts: It can implement flexible and dynamic management solutions. It can leverage emerging technologies; for example JMX solutions can use lookup and discovery services such as Jini network technology, UPnP, and Service Location Protocol (SLP).
Focuses on management: While JMX provides a number of services designed to fit into a distributed environment, its APIs are focused on providing functionality for managing networks, systems, applications, and services.
JMX Tiered Architecture
JMX Implementations
The Java 2 Platform, Standard Edition 5.0 (J2SE 5.0) supports JMX 1.2 and JMX Remote API 1.0, which is now the official JMX reference implementation (RI). For developers who are running J2SE 1.4, a JMX RI is also available from Sun Microsystems, and can be downloaded free of charge.
Sun Microsystems also provides the Java Dynamic Management Kit (Java DMK). Java DMK 5.1 is the first commercial implementation of the latest versions of the JMX standards, JMX 1.2 and JMX Remote API 1.0. JMDK is an all-in-one product for building secure, interoperable monitoring and management solutions on the J2SE platform, and it is supported on Solaris, Microsoft Windows, and Linux. Several other commercial and open source implementations are available as well. It is worth noting that Tomcat 5.0 implements the JMX specification.
JMX and J2SE 5.0
J2SE 5.0 has implemented version 1.2 of the JMX specification and version 1.0 of the JMX Remote API (JSR 160) specification. J2SE 5.0 includes significant monitoring and management features, including:
JVM instrumentation: The JVM is instrumented for monitoring and management providing built-in, out-of-the-box management capabilities for local and remote access.
Monitoring and Management APIs: The java.lang.management package provides the interface for monitoring and managing the JVM. It provides access to information such as: number of classes loaded and threads running, memory consumption, garbage collection statistics, on-demand deadlock detection, and others.
Management tools such as JConsole, which is a JMX-compliant monitoring tool that comes with J2SE 5.0. It uses JMX instrumentation of the JVM to provide information on performance and resource consumption of applications running on the Java platform.
The core classes for the JMX implementation are provided in the javax.management package. In addition, the java.lang.management package provides the mangagement interface for monitoring and management of the JVM as well as the operating system on which the JVM is running.
To enable the JMX agent and configure its operation using jconsole, your must set some specific system properties when you start the JVM. For local access, set the property com.sun.management.jmxremote as follows when starting the JVM:
prompt> java -Dcom.sun.management.jmxremote AppName
And, to enable monitoring and management from remote systems, set the property:
com.sun.management.jmxremote.port=portNumber
For more information on setting system properties for JMX, please see Monitoring and Management using JMX.
The JMX Programming Model
Using JMX to instrument your applications, services, or devices for manageability is simple. This is because JMX shares Java's object model. If you are familiar with Java and its JavaBeans component model, you already know 95% of all you need to know.
As mentioned previously, an MBean is a Java object that follows some standard design patterns and naming conventions. It can represent a device, application, or any resource that needs to be managed. An MBean exposes a management interface or a set of readable and/or writable attributes and a set of invokable operations, along with a self-description. Note that the management interface does not change through the life of an MBean instance.
Sample Application
This simple application manages a resource. You will create a simple standard MBean that exposes a String object and an operation. For more JMX examples, please see the JMX Tutorial.
The first step is to develop the MBean interface. In this application, the interface is called HelloMBean, which declares three methods: one getter, one setter, and one for saying hello as shown in Code Sample 1.
Code Sample 1: HelloMBean.java
public interface HelloMBean {
public void setMessage(String message);
public String getMessage();
public void sayHello();
}
The next step is to implement the MBean interface. A sample implementation is shown in the following Code Sample.
Code Sample 2: Hello.java
public class Hello implements HelloMBean {
private String message = null;
public Hello() {
message = "Hello there";
}
public Hello(String message) {
this.message = message;
}
public void setMessage(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
public void sayHello() {
System.out.println(message);
}
}
Congratulations! You have created your first MBean. The next step is to test the MBean, by developing a JMX agent in which you register the MBean. A JMX agent is a component in the agent level and acts as a container for the MBean. A sample agent, SimpleAgent, is provided in Code Sample 3. This agent performs the following tasks:
Gets the platform MBeanServer
Registers an instance of the Hello MBean
Code Sample 3: SimpleAgent.java
import javax.management.*;
import java.lang.management.*;
public class SimpleAgent {
private MBeanServer mbs = null;
public SimpleAgent() {
// Get the platform MBeanServer
mbs = ManagementFactory.getPlatformMBeanServer();
// Unique identification of MBeans
Hello helloBean = new Hello();
ObjectName helloName = null;
try {
// Uniquely identify the MBeans and register them with the platform MBeanServer
helloName = new ObjectName("SimpleAgent:name=hellothere");
mbs.registerMBean(helloBean, helloName);
} catch(Exception e) {
e.printStackTrace();
}
}
// Utility method: so that the application continues to run
private static void waitForEnterPressed() {
try {
System.out.println("Press to continue...");
System.in.read();
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String argv[]) {
SimpleAgent agent = new SimpleAgent();
System.out.println("SimpleAgent is running...");
SimpleAgent.waitForEnterPressed();
}
}
The java.lang.management.ManagementFactory class is a factory class for getting managed beans for the Java platform. In this example, the getPlatformMBeanServer() method is used to get the platform MBeanServer, which is the interface for MBean manipulation on the agent side. It contains the methods necessary for the creation, registration, and deletion of MBeans. The MBeanServer is the core component of the JMX infrastructure.
To experiment with this application, do the following:
Create a directory of your choice (such as jmx-example)
Copy Code Samples 1, 2, and 3 into that directory
Compile all the .java files using javac
Run SimpleAgent. In order to use the jconsole tool to manage it, you should run the SimpleAgent as follows:
prompt> java -Dcom.sun.management.jmxremote SimpleAgent
Note: The -Dcom.sun.management.jmxremote system property creates an RMI connector to the platform MBeanServer. For information on the RMI connector, see the coming section, Using the RMI Connector.
Connect to the JMX agent using the jconsole tool. Run the jconsole tool from the command line.
Once you start jconsole, it will display the list of local processes to be monitored as shown in Figure 2.
Figure 2: The jconsole monitoring tool
Now, you can connect to the service. Once connected, select the MBeans tab so that you can list the MBeans and manage them as shown in Figure 3.
Figure 3: The MBeans tab of jconsole
It is worth noting that local monitoring with jconsole is useful for development and prototyping. It is not recommended that jconsole be used locally for production environments as it consumes significant system resources. jconsole should be used on a remote system from the platform being monitored. For more information on jconsole and sample screenshots of what it provides, please see Using JConsole
JMX for Remote Management
The MBean server relies on protocol adaptors and connectors to make a JMX agent accessible from management applications outside the agent's JVM. Adaptors provide a view through a specific protocol for all MBeans registered in the MBean server (for example, an HTML adaptor could display an MBean in a Web browser). Connectors provide a manager-side interface that handles the communication between manager and JMX agent. When a remote management application uses this interface, it can connect to a JMX agent transparently through the network regardless of the protocol.
JMX technology exports JMX API instrumentation to remote applications by using Remote Method Invocation (RMI). It also defines an optional protocol based directly on TCP sockets called the JMX Messaging Protocol (JMXMP). However, note that this protocol is not supported in J2SE 5.0.
The JMX Remote API 1.0 (JSR 160) specification describes how to advertise and find JMX agents using existing discovery and lookup infrastructures. In other words, the specification does not define its own discovery and lookup service. Using existing discovery and lookup services is optional; you can encode the address of your JMX API agents in the form of URLs and make these URLs available to the manager.
Using the RMI Connector
Code Sample 4 shows an example of using the RMI connector, which is a slight modification of Code Sample 3.
Code Sample 4: SimpleAgent.java
import javax.management.*;
import java.lang.management.*;
import javax.management.remote.*;
public class SimpleAgent {
private MBeanServer mbs = null;
public SimpleAgent() {
// Get the platform MBeanServer
mbs = ManagementFactory.getPlatformMBeanServer();
// Unique identification of MBeans
Hello helloBean = new Hello();
ObjectName helloName = null;
try {
// Uniquely identify the MBeans and register them with the MBeanServer
helloName = new ObjectName("SimpleAgent:name=hellothere");
mbs.registerMBean(helloBean, helloName);
// Create an RMI connector and start it
JMXServiceURL url = new JMXServiceURL("service:jmx:rmi:///jndi/rmi://localhost:9999/server");
JMXConnectorServer cs = JMXConnectorServerFactory.newJMXConnectorServer(url, null, mbs);
cs.start();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String argv[]) {
SimpleAgent agent = new SimpleAgent();
System.out.println("SimpleAgent is running...");
}
}
To run this application, do the following:
If you wish to run this application on J2SE 1.4, you need to change the line mbs = ManagementFactory.getPlatformMBeanServer();
to mbs = MBeanServerFactory.createMBeanServer("SimpleAgent");
Compile the revised SimpleAgent.java from Code Sample 4.
Start the rmiregistry on port 9999 (prompt> rmiregistry 9999)
Run SimpleAgent (prompt> java SimpleAgent)
While SimpleAgent is running, run jconsole and then use the Advanced tab and enter the information as shown in the following figure.
Figure 4: Configuring jconsole for remote management
Once you are connected, you can browse the MBeans and manage them using the MBeans tab as shown in Figure 5.
Figure 5: Browsing and managing remote MBeans
Using the HTML Adaptor
An HTML adaptor is provided by Sun Microsystems and comes with the JMX Reference Implementation (it doesn't come with J2SE 5.0). The HTML adaptor lets you manage MBeans using a Web browser. The adaptor enables you to interact with the agent to view registered MBeans and their attributes. In other words, this adaptor provides a simple yet powerful management tool that lets you:
View the readable MBean attributes
Update writable attributes
Invoke methods
Code Sample 5 shows the revised SimpleAgent that uses the HTML adaptor.
Code Sample 5: SimpleAgent.java
import javax.management.*;
import java.lang.management.*;
import com.sun.jdmk.comm.HtmlAdaptorServer;
public class SimpleAgent {
private MBeanServer mbs = null;
public SimpleAgent() {
// Create an MBeanServer and HTML adaptor (J2SE 1.4)
mbs = ManagementFactory.getPlatformMBeanServer();
HtmlAdaptorServer adapter = new HtmlAdaptorServer();
// Unique identification of MBeans
Hello helloBean = new Hello();
ObjectName adapterName = null;
ObjectName helloName = null;
try {
// Uniquely identify the MBeans and register them with the MBeanServer
helloName = new ObjectName("SimpleAgent:name=hellothere");
mbs.registerMBean(helloBean, helloName);
// Register and start the HTML adaptor
adapterName = new ObjectName("SimpleAgent:name=htmladapter,port=8000");
adapter.setPort(8000);
mbs.registerMBean(adapter, adapterName);
adapter.start();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String argv[]) {
SimpleAgent agent = new SimpleAgent();
System.out.println("SimpleAgent is running...");
}
}
To experiment with this application, do the following:
Download the JMX Reference Implementation. This is needed only because SimpleAgent (in Code Sample 5) uses the HTML Adaptor, which does not come with the J2SE 5.0 implementation of JMX 1.2. From the JMX implementation, you only need the jmxtools.jar file.
If you wish to run this application on J2SE 1.4, you need to change the line mbs = ManagementFactory.getPlatformMBeanServer();
tombs = MBeanServerFactory.createMBeanServer("SimpleAgent");
Compile all the .java files (Code Samples 1, 2, and 5). Make sure you include the jmxtools.jar in your classpath.
Run SimpleAgent. Make sure you include the jmxtools.jar in your classpath. SimpleAgent will run as a server.
Connect to the JMX agent by entering the URL http://localhost:8000 in your web browser.
Once connected to the JMX agent, the HTML adaptor provides three views:
Agent view: Provides a summary of the MBeans contained within the agent. You can filter the MBean list to provide refined views.
Figure 6: HTML adaptor agent view
MBean view: Provides details about a specific MBean. Here you can set and get MBean attributes and invoke methods as shown in Figure 7.
Figure 7: HTML adaptor MBean view
Admin view: Allows you to register new MBeans on the agent as shown in Figure 8.
Figure 8: HTML admin view
JMX Related Specifications
The various JSRs that related to JMX follow:
JSR 3: JMX 1.2
JSR 77: J2EE Management
JSR 160: JMX Remote API 1.0
JSR 174: Monitoring and Management Specification for the JVM
JSR 255: JMX 2.0
JSR 262: Web Services Connector for JMX Agents
Summary
JMX provides a component-based architecture for developing solutions to monitor and manage your applications, services, and resources. JMX technology is the way to instrument any application or service that was built using Java technology. Hence, the Java platform now provides excellent facilities for creating and managing applications and services. JMX technology should be used for any application and service that benefit from being manageable, as this will increase their value to vendors and clients, by making them easier to install, configure, and maintain. The current version of JMX is 1.2, and the JMX 2.0 update was launched in September 2004. It will update the JMX and JMX Remote APIs to improve existing interfaces, mainly with respect to ease of use.
This article provided a fast track introduction and tutorial to JMX and its programming model. The sample code provided demonstrates how easy it is to get started developing management and monitoring solutions using JMX. The J2SE 5.0 implements the JMX specification—if you use J2SE 5.0, you are ready to start developing using JMX.
Related Information
Java Management Extensions (JMX)
Companies and products that use JMX technology
Monitoring and management in J2SE 5.0
Sun's Java Dynamic Management Kit (Java DMK)
Using JConsole to Monitor Java Applications
Acknowledgments
Special thanks to Mandy Chung and Eamonn McManus of Sun Microsystems, whose feedback helped me improve this article.
