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Creating a GWT Module

Hello world now done in GWT style. Instead of a static 'Hello World' page, a button will be placed on the web page that will display 'Hello World' when clicked.

Create a package under the root package called =client=. In that package, create a Java class named =ModuleNameApp= (e.g., =HelloWorldApp.java=). Put in the following code:

package edu.umiacs.gwt.hello.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.ClickListener;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.VerticalPanel;
import com.google.gwt.user.client.ui.Widget;

public class HelloWorldApp implements EntryPoint
{
    public void onModuleLoad()
    {
        GWT.log("onModuleLoad()", null);
        
        final Label lblSayHello = new Label();
        Button btnAsk = new Button("Say something");
        btnAsk.addClickListener(new ClickListener()
        {
            public void onClick(Widget w)
            {
                lblSayHello.setText("Hello world!");
            }
        });
        
        VerticalPanel vp = new VerticalPanel();
        vp.add(btnAsk);
        vp.add(lblSayHello);
        
        RootPanel root = RootPanel.get("div1");
        root.add(vp);
    }
    
}

Now modify the =ModuleName.gwt.xml= file (e.g., =HelloWorld.gwt.xml=) so that it now looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<module>
   <inherits name="com.google.gwt.user.User"/>      
   <entry-point class="edu.umiacs.gwt.hello.client.HelloWorldApp"/>        
</module>

The entry-point element should specify the fully qualified path to the class which implements =EntryPoint=. Now place the necessary information in the =ModuleName.html= file (e.g., =HelloWorld.html=). It should now contain the following:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
  <head>
    <title></title>
    <meta name='gwt:module' content='edu.umiacs.gwt.hello.HelloWorld'>
  </head>
  <body>
     <script language="javascript" src="gwt.js"></script>        
     <div id="div1"></div> 
  </body>
</html>

Run the project and click away!

  • Note:* During development, first run the project to bring up the shell. From that point on, it is not necessary to re-run the project on any changes. After making changes to the html or java files, just do a build (or even quicker--save all files) and reload in the GWT browser window.

-- Main.MikeMcGann - 27 Feb 2007