Home > Articles > Programming > Ajax

This chapter is from the book

This chapter is from the book

Building and Sharing Modules

Each GWT module is not necessarily a full application, but it can be used as a reusable library for other applications instead. The GWT module structure, also used for applications, gives you the tools necessary to package your module and share it with other applications. In fact, GWT itself is divided into several modules, as you've seen with the user interface, XML, JSON, HTTP, and RPC modules, so you've already used the process of importing other libraries.

Using Modules

GWT modules are distributed as jar files that you can include in your application by adding them to your project's classpath and inheriting their project name in your application's module file. This is the same process that you use to include the GWT library classes in your application. In this case GWT automatically adds the module jar file, gwt-user.jar, to your project's classpath when you generate the project using the GWT createProject script. The createApplication script then generates a module XML file for your application and automatically adds the com.google.gwt.user.User module to it. When we generate the module XML file for the Gadget Desktop application in Chapter 6, we get the following XML:

   <inherits name='com.google.gwt.user.User'/>
   <entry-point class='com.gwtapps.desktop.client.Desktop'/>

This module file tells the GWT compiler how to compile the application to JavaScript. The inherits element tells the compiler that we are using classes from the name module, which will also need to be compiled to JavaScript. We can continue to add modules from gwt-user.jar since the file is are already on the classpath. For new modules in other jar files, we first need to add the jar to the classpath. In Eclipse, you can do this by going to the project's Properties dialog and selecting the Libraries tab from Java Build Path, as shown in Figure 4-46.

Figure 4-46

Figure 4-46 Editing the build path in Eclipse

From here you can add and remove jar files. Notice that gwt-user.jar is already in the list. For the Gadget Desktop application we add the gwt-google-apis library to the project to use the Gears module from it. First, we add the gwt-google-apis jar to this list, and then the application's module XML file inherits the Gears module like this:

   <inherits name='com.google.gwt.user.User'/>
   <inherits name='com.google.gwt.json.JSON'/>
   <inherits name='com.google.gwt.xml.XML'/>
   <inherits name='com.google.gwt.gears.Gears'/>
   <entry-point class='com.gwtapps.desktop.client.Desktop'/>

Notice also that this project imports the JSON and XML modules which are already in the gwt-user.jar file. If you miss this step—adding the inherits tag to your application's module file—you will get an error from the GWT compiler that it can't find the module that you're using.

Creating a Reusable Module

If you've built a GWT application, you've already built a reusable module. The only difference is that your application has specified an entry point and can be turned into a GWT application loaded on its own in the GWT hosted mode browser or web browser. You could reference the application's module file from another application to reuse its components.

You create a module the same way you create an application, using GWT's applicationCreator script. You may want to use the ant flag with this script to build an ant file that will automatically package your module in a jar file for distribution.

The module structure of GWT is hierarchical using inheritance. For example, if you write a module that inherits GWT's User module, then any module or application that uses your module also automatically inherits GWT's User module. This is an important feature, since it allows the users of your module to automatically get all the requirements to run. GWT takes this concept further and lets you also inject resources into modules to ensure CSS or other JavaScript libraries are automatically included.

For example, if you were creating a module of widgets that required default CSS to be included, you could reference this in the module XML like this:

   <inherits name='com.google.gwt.user.User'/>
   <stylesheet src="widgets.css"/>

The widgets file would need to be included in your module's public files, and when other modules inherit your module they would automatically get the widgets.css file without directly including it.

You can similarly include JavaScript in your module using the script tag like this:

   <inherits name='com.google.gwt.user.User'/>

   <!-- Include google maps -->
   <script src="https://maps.google.com/

This tag is similar to the script tag that you would use in your HTML file to include a JavaScript library, except that this file would be automatically included with every module that includes this module.

As of GWT 1.4 you can use image bundles to include resources with your reusable modules. Image bundles allow you to package several images together into a single image for deployment. If you use an image bundle within your module, applications that use your module will automatically generate the single image. In Chapter 6, images bundles are used to build the Gadget toolbar in the Gadget Desktop application.

Sharing a Compiled Application (Mashups)

Sometimes you'd like to share your compiled JavaScript application for use on other web sites. As of GWT 1.4, other web sites can easily load your application using the cross-site version of the generated JavaScript. The cross-site version has –xs appended to the package name for the JavaScript file name, and you can find it in the www directory after compiling an application. For example, to include the Hangman application developed in Chapter 1, you would use the following script tag:

<script language='javascript' src='http://gwtapps.com/hangman/

Notice that this line differs from the line found in the original host HTML page for the application; it has the addition of –xs in the filename and is loading the script from the gwtapps.com domain.

Each application that you share may have additional requirements for integration on another site. In the Hangman example, the application looks for an HTML element with the ID hangman, so anyone including this on their site would need to also have the following HTML in the location where they'd like the Hangman application to show up:

<div id="hangman"></div>

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020