Spring and GWT Integration using Maven and GWTHandler (Part 1)

In this tutorial we will setup a simple GWT application and integrate it with Spring. We will use GWTHandler to map GWT's RPC services to Spring beans, and utilize Maven to manage and build our project. Our application is the typical GWT Hello application we see when we create a new GWT project.

Note: An updated version of this guide is available at Spring 3.1: GWT Maven Plugin and GWTHandler Integration

What is GWTHandler?

The GWTHandler allows you to quickly map multiple RPC service beans to different URLs very similar to the way Spring's SimpleUrlHandlerMapping maps URLs to controllers. The
mapped beans are internally wrapped into GWTRPCServiceExporter
instances

Source: http://gwt-widget.sourceforge.net/?q=node/54

What is GWT?

Google Web Toolkit (GWT) is a development toolkit for building and optimizing complex browser-based applications. GWT is used by many products at Google, including Google AdWords and Orkut. It's open source, completely free, and used by thousands of developers around the world.

Source: http://code.google.com/webtoolkit/

What is Spring?

[T]he leading platform to build and run enterprise Java applications. Led and sustained by SpringSource, Spring delivers significant benefits for many projects, increasing development productivity and runtime performance while improving test coverage and application quality.

Source: http://www.springsource.org/

What is Maven?

Apache Maven is a software project management and comprehension tool. Based on the concept of a project object model (POM), Maven can manage a project's build, reporting and documentation from a central piece of information.

Source: http://maven.apache.org/

Here's what we will be building:

Initial run: plain GWT

Final run: GWT and Spring

Now that you've seen what we'll be building, let's create our project.

I assume you're running Eclipse with m2eclipse installed (or Spring's STS). If you don't have any of these, please visit the following links:

- Eclipse: http://www.eclipse.org/downloads/
- m2eclipse: http://m2eclipse.sonatype.org/

or

- STS: http://www.springsource.com/products/springsource-download-center

1. Open your IDE. Create a New Project

2. Select Maven. Then select Maven Project.

3. On the Select an Archetype screen, choose gwt-maven-plugin. Make sure the version is 2.1.0-1 or greater! If not, update your catalog.

4. Click Next. On the Specify Archetype parameters window, enter an appropriate Artifact Id and Package. Then make sure you add a value on the module parameter. If you're new to GWT, just follow the values from the screenshot below:

5. Click Finish when you're done. You should see the following project structure:

Notice there are multiple red markers. These mean something is wrong with our project. Upon checking all files, we realize the Async interfaces needs to be created first!

To resolve this, we can manually create the Async interfaces. However, Maven has a goal support to automatically generate the Async interfaces. For more info, please visit http://mojo.codehaus.org/gwt-maven-plugin/examples/asyn.html

We will be using the generateAsync goal to generate the interfaces.

6. Right-click on your project. Select Run As. Then Select Run Configurations

7. Find the Maven Build section on the Run Configurations window

8. Press the New button to create a new Maven Build configuration.

9. Enter the following details for this new configuration:

Name: generateAsync
Base directory: (click on Browse and find your project)
Goals: gwt:generateAsync

10. Click Apply. Click Run. You should see the following output on the Console window:

[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building GWT Maven Archetype 1.0.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- gwt-maven-plugin:2.1.0-1:generateAsync (default-cli) @ spring-gwt-integration ---
[WARNING] Encoding is not set, your build will be platform dependent
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.316s
[INFO] Finished at: Fri Jan 07 23:49:31 2011
[INFO] Final Memory: 6M/124M
[INFO] ------------------------------------------------------------------------

The Async interfaces are generated automatically. But where are they saved?

11. Go your project directory. Open the target folder, and you will see the generated-sources folder. This is where Maven saved the Async interfaces. Expand the sub-folders until you find the Async interfaces: GreetingServiceAsync.java and Messages.java

12. Copy these files and paste them on the client package. In my case, it's org.krams.tutorial.client

Notice most of the red warnings are now gone, but there's still one left. That's because Eclipse is complaining that we have set the wrong output directory, but in fact, we didn't. You can safely ignore this warning.

Now let's run our project and see how it would look like. We will be using Maven again to run the application. We cannot use the usual Run As >> Web Application command here because we're using Maven.

To run the application, we'll use the gwt:run goal.

13. To create the Maven gwt:run goal, follow the same exact steps when we created the generateAsync goal. But of course, you will need to change the details to the following:

Name: gwt-run
Base directory: (click on Browse and find your project)
Goals: gwt:run

14. Click Apply. Click Run. The GWT Development Mode window will appear.

15. Click on Launch Default Browser to run the application. Or you may copy the link and paste it in your browser.

You should see the following application:

Play with the application. Close it when you're done. What we saw here is the GWT application.

Our next task is to integrate this application with Spring. Visit the following link for the continuation: Spring and GWT Integration using Maven and GWTHandler (Part 2)

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