RHQ tip of the day: Overseer API (updated)

Sometimes it is necessary in RHQ-plugins to load resources when the plugin is loaded and more important to unload those when the plugin is unloaded from the plugin container.

( As you can see from the comments, Mazz has renamed the Interface class, so I updated this article. )

Mazz has recently added the PluginOverseer PluginLifecycleListener interface for exactly this purpose (see e.g RHQ-1584).

To use the api, you need to do two things:

• Implement the interface org.rhq.core.pluginapi.plugin.PluginLifecycleListener
  
• Wire the implementation class in the plugin descriptor.
  

With the following entry in the plugin descriptor, rhq-plugin.xml


<plugin name="MyPlugin"

  package="org.rhq.plugins.myPlugin"

  pluginLifecycleListener="MyPluginOverseer" .../>


The code for this could look like this:


package org.rhq.plugins.myPlugin;

import org.rhq.core.pluginapi.plugin.PluginContext;

import org.rhq.core.pluginapi.plugin. PluginLifecycleListener;

 



public class MyPluginOverseer

  implements PluginLifecycleListener {


  Class clazz;

// called on plugin load

public void initialize( PluginContext context ) {

  ...

  clazz = Class.forName("org.acme.Driver");

  ...

}

// called on plugin unload

public void shutdown() {

  clazz = null;

  }

}


There are some real examples of the usage of this API, like e.g. in the Postgres-plugin.

As this API is added to RHQ, it applies to Jopr (trunk) and the upcoming release of JBoss ON as well.

I have also updated the plugin generator to support this new API - its version is now 1.2.1.