src: This folder contains all the generated source and configuration files for the applications, contained in the familiar Java package structure, with the root package being com.packtpub.gwtbook.hellogwt. This package name was deduced by applicationCreator from the fully qualified class name that we provided as a parameter to it. The generated files under this directory are:

compacktpubgwtbookhellogwtHelloGWT.gwt.xml: This is the project module--an XML file that holds the entire configuration needed by a GWT project. The inherits tag specifies modules inherited by this module. In this simple case, we are inheriting only the functionality provided by the User module, which is built into the GWT. On more complex projects, module inheritance provides a nice way to reuse pieces of functionality. The EntryPoint refers to the class that will be instantiated by the GWT framework when the module is loaded. This is the class name provided to the applicationCreator command, when we created the project. The following code can be found in this file:

compacktpubgwtbookhellogwtclientHelloGWT.java: This is the entry point for our application. It extends the EntryPoint class, and when the HelloGWT module is loaded by the GWT framework, this class is instantiated and its onModuleLoad() method is automatically called. In this generated class, the onModuleLoad() method creates a button and a label, and then adds them to the page. It also adds a click listener for the button. We will be modifying the code in HellowGWT.java to create a new application later in this chapter. The current code in this file is as follows:

package com.packtpub.gwtbook.hellogwt.client;
import com.google.gwt.core.client.EntryPoint;
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.Widget;

/** Entry point classes define onModuleLoad(). */
public class HelloGWT implements EntryPoint
{
   /** This is the entry point method. */
   public void onModuleLoad()
   {
        final Button button = new Button("Click me");
        final Label label = new Label();
        button.addClickListener(new ClickListener()
        {
        public void onClick(Widget sender)
        {
        if (label.getText().equals(""))
        label.setText("Hello World!");
        else
        label.setText("");
        }
        }
        //Assume that the host HTML has elements defined whose
        //IDs are "slot1", "slot2". In a real app, you probably
        //would not want to hard-code IDs. Instead, you could,
        //for example, search for all elements with a
        //particular CSS class and replace them with widgets.
        RootPanel.get("slot1").add(button);
        RootPanel.get("slot2").add(label);
    }

compacktpubgwtbookhellogwtpublicHelloGWT.html: This is a generated HTML page that loads the HelloGWT application and is referred to as the host page, as this is the web page that hosts the HelloGWT application. Even though this HTML file is deceptively simple, there are some points that you need to be aware of:

o Firstly, it contains a meta tag that points to the HelloGWT module directory. This tag is the connection between the HTML page and the HelloGWT application. The following code represents this connection:

content='com.packtpub.gwtbook.hellogwt.HelloGWT'>

o Secondly, the script tag imports code from the gwt.js file. This file contains the code (shown below) required to bootstrap the GWT framework. It uses the configuration in the HelloGWT.gwt.xml file, and then dynamically loads the JavaScript created by compiling the HelloGWT.java file to present the application. The gwt.js file does not exist when we generate the skeleton project. It is generated by the GWT framework when we run the application in hosted mode or when we compile the application.

HelloGWT-compile.cmd: This file contains a command script for compiling the application into HTML and JavaScript.

HelloGWT-shell.cmd: This file contains a command script for running the application in the hosted mode.

There is a well-defined relationship between these generated files. The HelloGWT.html file is the host page that loads the gwt.js file.

There's More!

The applicationCreator provides options to control several parameters for a
new application. You can see these options by executing it from the following command line:

applicationCreator.cmd -help

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