Developing Struts PlugIn – 飛奔嘅蝸牛

This article shows you how to develop custom Struts PlugIn and incorporate in your Struts Web Applications. After completing this tutorial you will be able to create your own custom PlugIn for your web application. Struts PlugIn allows the programmer to enhance their web applications. There are many PlugIns available for struts e.g. Struts Tiles PlugIn, Struts Hibernate PlugIn, Struts Spring PlugIn etc. Beside these available PlugIn you can create your own PlugIn.

Understanding PlugIn

Struts PlugIns are configured using the <plug-in> element within the Struts configuration file. This element has only one valid attribute, ‘className’, which is the fully qualified name of the Java class which implements the org.apache.struts.action.PlugIn interface.

For PlugIns that require configuration themselves, the nested <set-property> element is available.

The plug-in tag in the struts-config.xml file is used to declare the PlugIn to be loaded at the time of server start-up. Following example shows how to declare the Tiles PlugIn:

<plug-in className=”org.apache.struts.tiles.TilesPlugin”>
    <set-property
        property=”definitions-config”
           value=”/WEB-INF/tiles-defs.xml”/>
</plug-in>

The above declaration instructs the struts to load and initialize the Tiles plugin for your application on startup.

Writing Struts PlugIn Java Code

In this example we write HelloWorld Struts PlugIn example that will give you idea about creating, configuring and checking Struts PlugIn. Our HelloWorld Stuts PlugIn contains a method called Say Hello, which simply returns HelloWorld message.

Here is code of HelloWorld Struts Plugin:

package roseindia.net.plugin;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import org.apache.struts.action.PlugIn;
import org.apache.struts.action.ActionServlet;
import org.apache.struts.config.ModuleConfig;

/**
* @author Deepak Kumar
* @Web http://www.roseindia.net
* @Email roseindia_net@yahoo.com
*/


public class HelloWorldStrutsPlugin implements PlugIn {


    public static final String PLUGIN_NAME_KEY 
            = HelloWorldStrutsPlugin.class.getName();

   public void destroy() {
      System.out.println(“Destroying Hello World PlugIn”);
   }

   public void init(ActionServlet servlet, ModuleConfig config) 
throws ServletException {
      System.out.println(“Initializing Hello World PlugIn”);
   ServletContext context = null;
   context = servlet.getServletContext();
   HelloWorldStrutsPlugin objPlugin = new HelloWorldStrutsPlugin();
   context.setAttribute(PLUGIN_NAME_KEY, objPlugin);

   }

  public String sayHello(){
    System.out.println(“Hello Plugin”);
    return “Hello Plugin”;
  }
  
}

Configuring PlugIn

To configure the plugin add the following line your struts-config.xml file.

<plug-in className=”roseindia.net.plugin.HelloWorldStrutsPlugin”>
</plug-in>

Calling PlugIn From JSP Page

Here is the code for calling our PlugIn from jsp page.

<%@page contentType=”text/html” import=”java.util.*,roseindia.net.plugin.*” %>
<%

ServletContext servletContext = this.getServletContext();

HelloWorldStrutsPlugin plugin= (HelloWorldStrutsPlugin) servletContext.getAttribute
(HelloWorldStrutsPlugin.PLUGIN_NAME_KEY);

String strMessage = plugin.sayHello();

%>

Message From Plugin: <%=strMessage%>

Building and Testing

Use ant tool to build the application and then deploy on the server. Enter the url http://localhost:8080/strutstutorial/pages/plugin.jsp in your browser. It display “Hello Plugin” message. Your server console also should display “Hello Plugin” message.

In this section we learnt how to develop simple struts plugin, configure, deploy and test.

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