Java EE Web App插件架构

Question

I have a simple Web App that receives data via a web service and persists it in a database. I am using CXF, Hibernate and Glassfish 3. I am very new to all of this, however I am trying to work out how I can develop a simple plugin model so that when the App fisrt starts up it searches for plugin's in a folder and calls an instantiation(?) class for each plugin. The issue is that I am not really sure how to initiate this process (that is when the App firsts starts) - how do I know when the app first starts. Any advice/comments appreciated!

ok here is a sample class with the modification of web.xml:

package foo.bar.startup;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class AppStartup implements ServletContextListener {

    public void contextInitialized(ServletContextEvent event) {
        // App started - do start up stuff
    }
    public void contextDestroyed(ServletContextEvent event) {
        // App stopped - do something
    }
}




  <listener>
    <listener-class>foo.bar.AppStartup</listener-class>
  </listener>

Answer 1

If you want to know when the app starts / stops, you can implement a ServletContextListener and register it in the web.xml file.

You should look at OSGI - if you need an elaborate plugin model, with support for deploying new plugins at runtime, hot redeployment of plugins etc.

Answer 2

When a web application starts, it fires a ServletContextEvent which goes to every registered ServletContextListener . These listeners must be configured in the web.xml of the application:

<listener>
    <listener-class>com.foo.bar.MyServletContextListener</listener-class>
</listener>