Today, I want to share how to learn GWT 2.8 with Maven GWT Plugin. I wrote this post because the official GWT tutorial has some inconvenience: source code and resources are stored as GWT standard structure, commands must be launched from Apache Ant, JARs and classpath must be handled explicitly etc. I found it more comfortable to start with Maven, the tool which many Java developers are familiar with. Before getting started, please be sure that the following tools are installed in your computer:

  • JDK 8
  • Maven 3

Create a Project

Build a sample GWT application with Maven is easy. You can use the archetype provided by GWT Maven plugin. An archetype is defined as an original pattern or model from which all other things of the same kind are made. Suppose that you want to create a GWT application for group com.mycompany, artifact my-app, version 1.0-SNAPSHOT, and GWT module called MyModule. Then you can create your project in the following batch mode:

$ mvn -B archetype:generate \
    -DarchetypeGroupId=org.codehaus.mojo \
    -DarchetypeArtifactId=gwt-maven-plugin \
    -DarchetypeVersion=2.8.1 \
    -DgroupId=com.mycompany \
    -DartifactId=my-app \
    -Dversion=1.0-SNAPSHOT \
    -Dmodule=MyModule

Otherwise, you can create your project in interactive mode. And fill all the required parameters in your terminal:

$ mvn archetype:generate \
    -DarchetypeGroupId=org.codehaus.mojo \
    -DarchetypeArtifactId=gwt-maven-plugin \
    -DarchetypeVersion=2.8.1

No matter which mode you used, the result should be successful:

...
[INFO] ----------------------------------------------------------------------------
[INFO] Using following parameters for creating project from Archetype: gwt-maven-plugin:2.8.1
[INFO] ----------------------------------------------------------------------------
[INFO] Parameter: groupId, Value: com.mycompany
[INFO] Parameter: artifactId, Value: my-app
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] Parameter: package, Value: com.mycompany
[INFO] Parameter: packageInPathFormat, Value: com/mycompany
[INFO] Parameter: package, Value: com.mycompany
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] Parameter: groupId, Value: com.mycompany
[INFO] Parameter: module, Value: MyModule
[INFO] Parameter: artifactId, Value: my-app
[INFO] Project created from Archetype in dir: /Users/mincong/Desktop/my-app
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 7.858 s
[INFO] Finished at: 2018-01-29T21:51:53+01:00
[INFO] Final Memory: 22M/1039M
[INFO] ------------------------------------------------------------------------

Understand GWT Project Structure

In the next step, we’ll explore the project structure created by Maven GWT plugin.

$ tree my-app/
my-app/
├── pom.xml
├── src
│   ├── main
│   │   ├── java
│   │   │   └── com
│   │   │       └── mycompany
│   │   │           ├── client
│   │   │           │   ├── GreetingService.java
│   │   │           │   ├── Messages.java
│   │   │           │   └── MyModule.java
│   │   │           ├── server
│   │   │           │   └── GreetingServiceImpl.java
│   │   │           └── shared
│   │   │               └── FieldVerifier.java
│   │   ├── resources
│   │   │   └── com
│   │   │       └── mycompany
│   │   │           ├── MyModule.gwt.xml
│   │   │           └── client
│   │   │               └── Messages_fr.properties
│   │   └── webapp
│   │       ├── MyModule.css
│   │       ├── MyModule.html
│   │       └── WEB-INF
│   │           └── web.xml
│   └── test
│       ├── java
│       │   └── com
│       │       └── mycompany
│       │           └── client
│       │               └── GwtTestMyModule.java
│       └── resources
│           └── com
│               └── mycompany
│                   └── MyModuleJUnit.gwt.xml
└── target
    └── generated-sources
        └── gwt
            └── com
                └── mycompany

27 directories, 13 files

As you can see, 27 directories and 13 files have been created.

Application Source Folder

src/main/java, the application source folder, it contains only Java files. Such files are separated in 3 categories: client, server, and shared. Client files will be transpiled from Java to JavaScript, and be executed in user’s browser. Server files will be compiled into bytecode, and be executed on the server as normal Java files. Shared files are different. They will be shared between client side and server side, via RPC—Remove Procedure Call.

Application Resources Folder

src/main/resources, the application resources folder, it contains the GWT module definition, written in XML file. Module XML files is resided in project’s root package. Its related path to resources folder is:

./com/mycompany/MyModule.gwt.xml

Such naming convention helps GWT to define the logical name of the module:

com.mycompany.MyModule

Web Application Sources Folder

src/main/webapp, the web application sources, it contains static resources used by the web application, and the deployment descriptor file web.xml. Notice that when using the DevMode, the resources in this folder are not refreshable.

Test Sources Folder

src/test/java, the test sources, it contains GWT tests. GWT tests are different from classical unit tests. They are transpiled from Java to JavaScript before being executed. GWT includes a special GWTTestCase base class that provides JUnit integration. Running a compiled GWTTestCase subclass under JUnit launches the HtmlUnit browser which serves to emulate your application behavior during test execution. Since these tests are launched in browser, they are actually integration tests. Naming test as GwtTest means:

  • They won’t be executed at test phrase (avoid matching *Test and Test*).
  • They will be executed at verify phrase by Maven GWT Plugin.
  • They won’t be executed as normal integration tests by Maven Failsafe Plugin.

Test Resources Folder

src/test/resources, the test resources, is very similar to application resources.

Run DevMode

The standard src/main/webapp webapp folder is used by Maven GWT Plugin to run the dev mode server (Jetty).

mvn gwt:run

And you can now see the GWT Development Mode. When clicking the button “Launch Default Browser”, you can see the result in your browser:

Dev Mode in localhost

Testing

The Maven GWT Plugin testing support is not intended to be run standalone, rather it is bound to the Maven integration-test phase. To get gwt:test to run, you should include the test goal in your plugin configuration executions, and you should invoke mvn verify (or mvn install).

mvn verify

Conclusion

Today we learnt how to use GWT Maven Plugin to create a quick start project by following the standard Maven layouts. Some basic thinking about the different folders. We also use the 2 basics Maven commands for running application in development mode, and running GWT tests. Hope you enjoy this post, see you the next time.

References