Jakarta Struts Cookbook

2.1. Using Plug-ins for Application Initialization

Problem

You want to load initial data into the application context when your application starts up.

Solution

Create a class that implements the org.apache.struts.action.PlugIn interface and specify the plug-in element in the struts-config.xml. The following XML fragment shows a plug-in declaration and a nested set-property element for setting a custom property:

<plug-in className="com.oreilly.strutsckbk.CustomPlugin" >


  <set-property property="customData"


                   value="Hello from the plugin"/>


</plug-in>

Discussion

Struts provides a PlugIn interface you can use to create custom services that are initialized on application startup. The Java source for the PlugIn interface is shown in Example 2-1. (For clarity, the JavaDoc documentation has been removed from this listing.)

Example 2-1. The Struts PlugIn interface

package org.apache.struts.action;

import javax.servlet.ServletException;
import org.apache.struts.config.ModuleConfig;

public interface PlugIn {

    public void destroy( );

    public void init(ActionServlet servlet, ModuleConfig config)
        throws ServletException;
}

To implement a plug-in, you only need to implement this interface and declare the plug-in implementation in the struts-config.xml file. The two methods that must be implemented, init() and destroy( ), are called during the lifecycle of the plug-in. Struts calls the init( ) method after it instantiates the plug-in on startup of the ActionServlet. Struts calls the destroy() method when ...