Tutorial

The standard approach in Java is to have separated projects for separate purposes. For example the domain model of the application is usually defined in its own project. One way of making these classes available to GWT is to copy them into the package "client" in your GWT project. This is bad practice as it leads to code duplication (which is inherently evil). This chapter describes how you can make these projects available to the GWT compiler as modules.

GWT need to have access to the source files to compile them into Javascript code. If you add the project or the jar file to your GWT classpath then the Java compiler will not complain if you use the classes from the included project / jar but the GWT compiler will not be able to compile them.

To make the Java files available to the GWT compiler you need to

Create a Java project "de.vogella.gwt.module.model" and package "de.vogella.gwt.module.model". Create the following class.

				
package de.vogella.gwt.module.model;

public class Person {
	private String firstName;

	
/**
	 * @return the firstName
	 */
	public String getFirstName() {
		return firstName;
	}

	
/**
	 * @param firstName
	 *            the firstName to set
	 */
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

}

			

Create in package "de.vogella.gwt.module" the file "model.gwt.xml" with the following content. This will be the module definition for GWT.

				
<module>
  <inherits name='com.google.gwt.user.User'/>
  <source path="model"></source>
</module>
			

We want to use this model in a GWT project. Create therefore a new GWT project "de.vogella.gwt.module.application" similar to the first example of this article with the following entry point.

				
package de.vogella.gwt.module.application.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;

import de.vogella.gwt.module.model.Person;

public class ModulTest implements EntryPoint {

	@Override
	public void onModuleLoad() {
		Person p = new Person();
		p.setFirstName("Lars");
		Label label = new Label("Hello " + p.getFirstName());
		RootPanel.get().add(label);
	}
}

			

To make the module project available for the Java compiler, right-click your project, select properties -> Java Build Path and add a dependency to the project "de.vogella.gwt.module.model".

Make the Java class of your new module available to the GWT compiler by using "inherits" in your file "De_vogella_gwt_module_application.gwt.xml".

				
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 1.6.4//EN" "http://google-web-toolkit.googlecode.com/svn/tags/1.6.4/distro-source/core/src/gwt-module.dtd">
<module rename-to='de_vogella_gwt_module_application'>
  <!-- Inherit the core Web Toolkit stuff.                        -->
  <inherits name='com.google.gwt.user.User'/>

  <inherits name='com.google.gwt.user.theme.standard.Standard'/>
  <inherits name='de.vogella.gwt.module.model'/>

  <!-- Other module inherits                                      -->

  <!-- Specify the app entry point class.                         -->
  <entry-point class='de.vogella.gwt.module.application.client.ModulTest'/>
</module>

			

If everything was setup correctly you can run your application.

GWT Homepage

GWT Widgets Overview

Declaritive UI's for GWT applications

Google group for GWT

Large scale application development and MVP - Part I

Large scale application development and MVP - Part II