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Chapter 8. JBoss EAP MBean Services

A managed bean, sometimes simply referred to as an MBean, is a type of JavaBean that is created with dependency injection. MBean services are the core building blocks of the JBoss EAP server.

8.1. Writing JBoss MBean Services
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Writing a custom MBean service that relies on a JBoss service requires the service interface method pattern. A JBoss MBean service interface method pattern consists of a set of life cycle operations that inform an MBean service when it can create, start, stop, and destroy itself.

You can manage the dependency state using any of the following approaches:

  • If you want specific methods to be called on your MBean, declare those methods in your MBean interface. This approach allows your MBean implementation to avoid dependencies on JBoss specific classes.
  • If you are not bothered about dependencies on JBoss specific classes, then you may have your MBean interface extend the ServiceMBean interface and ServiceMBeanSupport class. The ServiceMBeanSupport class provides implementations of the service lifecycle methods like create, start, and stop. To handle a specific event like the start() event, you need to override startService() method provided by the ServiceMBeanSupport class.

8.1.1. A Standard MBean Example
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This section develops two sample MBean services packaged together in a service archive (.sar).

ConfigServiceMBean interface declares specific methods like the start, getTimeout, and stop methods to start, hold, and stop the MBean correctly without using any JBoss specific classes. ConfigService class implements ConfigServiceMBean interface and consequently implements the methods used within that interface.

The PlainThread class extends the ServiceMBeanSupport class and implements the PlainThreadMBean interface. PlainThread starts a thread and uses ConfigServiceMBean.getTimeout() to determine how long the thread should sleep.

Example: MBean Services Class

package org.jboss.example.mbean.support;
public interface ConfigServiceMBean {
    int getTimeout();
    void start();
    void stop();
}
package org.jboss.example.mbean.support;
public class ConfigService implements ConfigServiceMBean {
    int timeout;
    @Override
    public int getTimeout() {
        return timeout;
    }
    @Override
    public void start() {
        //Create a random number between 3000 and 6000 milliseconds
        timeout = (int)Math.round(Math.random() * 3000) + 3000;
        System.out.println("Random timeout set to " + timeout + " seconds");
    }
    @Override
    public void stop() {
        timeout = 0;
    }
}

package org.jboss.example.mbean.support;
import org.jboss.system.ServiceMBean;
public interface PlainThreadMBean extends ServiceMBean {
    void setConfigService(ConfigServiceMBean configServiceMBean);
}

package org.jboss.example.mbean.support;
import org.jboss.system.ServiceMBeanSupport;
public class PlainThread extends ServiceMBeanSupport implements PlainThreadMBean {
    private ConfigServiceMBean configService;
    private Thread thread;
    private volatile boolean done;
    @Override
    public void setConfigService(ConfigServiceMBean configService) {
        this.configService = configService;
    }
    @Override
    protected void startService() throws Exception {
        System.out.println("Starting Plain Thread MBean");
        done = false;
        thread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    while (!done) {
                        System.out.println("Sleeping....");
                        Thread.sleep(configService.getTimeout());
                        System.out.println("Slept!");
                    }
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }
        });
        thread.start();
    }
    @Override
    protected void stopService() throws Exception {
        System.out.println("Stopping Plain Thread MBean");
        done = true;
    }
}
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The jboss-service.xml descriptor shows how the ConfigService class is injected into the PlainThread class using the inject tag. The inject tag establishes a dependency between PlainThreadMBean and ConfigServiceMBean, and thus allows PlainThreadMBean use ConfigServiceMBean easily.

Example: jboss-service.xml Service Descriptor

<server xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="urn:jboss:service:7.0 jboss-service_7_0.xsd"
        xmlns="urn:jboss:service:7.0">
 <mbean code="org.jboss.example.mbean.support.ConfigService" name="jboss.support:name=ConfigBean"/>
 <mbean code="org.jboss.example.mbean.support.PlainThread" name="jboss.support:name=ThreadBean">
  <attribute name="configService">
   <inject bean="jboss.support:name=ConfigBean"/>
  </attribute>
 </mbean>
</server>
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After writing the MBeans example, you can package the classes and the jboss-service.xml descriptor in the META-INF folder of a service archive (.sar).

8.2. Deploying JBoss MBean Services
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Deploy and test sample MBeans in managed domain

Use the following command to deploy the sample MBeans (ServiceMBeanTest.sar) in a managed domain: 

deploy ~/Desktop/ServiceMBeanTest.sar --all-server-groups
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Deploy and test sample MBeans on a standalone server

Use the following command to build and deploy the sample MBeans (ServiceMBeanTest.sar) on a standalone server: 

deploy ~/Desktop/ServiceMBeanTest.sar
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Undeploy sample MBeans

Use the following command to undeploy the sample MBeans: 

undeploy ServiceMBeanTest.sar
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