Java Magazine - May/June 2012

//enterprise java /

@Path("configuration")

@Produces(TEXT_PLAIN)

@LocalBean @Singleton public class Configurator implements ConfiguratorMXBean {

LISTING 19 LISTING 20

COMMUNITY

Figure 1

private ObjectName objectName; private MBeanServer platformMBeanServer;

the MXBean ending and register the Singleton instance at the JMX runtime:

public interface ConfiguratorMXBean { String getConfiguration(); } bute or the name of the key in the configuration, which could break the system at runtime.

@PostConstruct public void fetchConfiguration() { //... mergeWithCustomConfiguration(); registerInJMX();

}

JAVA IN ACTION

The Configurator first has to be registered at the JMX runtime. The @PostConstruct method Configurator#fetchConfiguration invokes the Configurator#registerInJMX, which performs the JMX registration (see Listing 19).

Equally important is the unregistra-tion of the Configurator at shutdown time, destroy time, or undeploy time. The method Configurator#unregisterFromJMX unregisters the Configurator from the MBeanServer. Without this important task, you can’t redeploy your application. After the deployment, the Configurator with its configuration becomes visible in the Java Monitoring and Management Console (JConsole), as shown in Figure 1.

void registerInJMX(){ try { objectName = new ObjectName("Configurator:type=" + this.getClass().getName()); platformMBeanServer = ManagementFactory.getPlatformMBeanServer(); platformMBeanServer.registerMBean(this, objectName); } catch (Exception e) { throw new IllegalStateException("..." + e); } }

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Think About the Stakeholders

With Java EE 6, it is trivial to configure all components of an application. It is even possible to change the configuration on every request/transaction and change it via REST, JMX, SOAP, IIOP, or any other available protocol.

Before you eagerly make everything in your system configurable, first think about the stakeholders and the real requirements. Usually, no one wants (or actually dares) to change configuration entries in the running system; if you change the configuration entries,

@PreDestroy public void unregisterFromJMX() { try { platformMBeanServer.unregisterMBean(this.objectName); } catch (Exception e) { throw new IllegalStateException("...:" + e);

} //...other methods omitted }

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Keeping Things Consistent The coupling between the attributes and the configuration store is loose. You can accidentally change a name of the attri-you will have to retest and redeploy your application anyway.