The flat project structure

One of the major problems that occur when using Maven and Eclipse together, is that Maven encourages the use of deep project structures, whereas eclipse can't handle those. A solution to this problem is to force Maven to use the flat structure:

.....
<modules>
  <module>../module1</module>
  <module>../module2</module>
</modules>
.....

This has some very big drawbacks: You will lose the possibility to use several of Maven's tools (eg the release-plugin), because these are unable to handle flat structures.

The best approach is to do everything the way it was intended in Maven, and let the maven-eclipse-plugin bend WTP to its will. Therefore, the recommendation would be to use the deep structures:

.....
<modules>
  <module>module1</module>
  <module>module2</module>
</modules>
.....

The Example project

This project is an example of a multi-module projects, containing some JAR-, a WAR- and an EAR-project. You can download it from here. The project is based on the j2ee-simple archetype.

Source Control Management

Eclipse and Maven support a wide range of SCM systems (like CVS and SVN). The usage in a WTP/Maven project has some peculiarities, which we will discuss below.

.classpath
.project
.settings
target

Multi Project Import/Export Plugin

There is an Eclipe plugin available that can help a lot when using multi-module projects. This plugin can import several projects at once, and it can do so from both a deep and a flat structure.

The plugin is called "Multi Project Import/Export Plugin" and can be found here. You can also reference the update site in eclipse, using the URL: http://eclipse-tools.sourceforge.net/updates/

Project names

The project names in Eclipse do not have to be the same as the name of the folder. Instead of forcing Maven to generate artifacts without version name (which is considered bad practice), the maven-eclipse-plugin can adapt the project names to include the version name! This way the artifact Eclipse generates, will have the same name as the artifact the Maven generates!

Many problems in the area of "the eclipse exported ear works, but the maven generated not" (or vice-versa) come from this different "final name" problem.

The best way to evade such problems is to use this setting for the maven-eclipse-plugin:

<projectNameTemplate>[artifactId]-[version]</projectNameTemplate>

The pom modules

The root of the projects in Maven is always a POM-module. These projects can be imported into Eclipse as well, which then enables you to create and use External Tool-launches with workspace-locations. This makes the launches also exchangeable between developers and they can therefore also be stored in SCM.

Maven builds as launches

As was said above, it is very useful to have your Maven builds inside Eclipse as a Launch-configuration. To create these, you should create a new External Tool and fill out the following values:

• Name:

  The name for the launch -- this can be chosen freely.

• Location:

    ${env_var:JAVA_HOME}/bin/java

  If you're on Windows, you should add the '.exe' extension to the above command.

  Or, if you really want to make the builds interoperable, all developers should create a variable in their workspace called 'JAVA_EXECUTABLE', holding either the value 'java' (linux) or 'java.exe' (windows). The above command can then be changed into

    ${env_var:JAVA_HOME}/bin/${JAVA_EXECUTABLE}

• Working Directory:

  Select the root pom project here.

    ${workspace_loc:/j2ee-simple}

• Arguments:

  In the example below, we presume you have made the organization-project containing the Maven distribution. The project is called 'organization'.

    -Dclassworlds.conf=${resource_loc:organization/maven-2.0/bin/m2.conf} 
    -Dmaven.home=${resource_loc:organization/maven-2.0}
    -classpath ${resource_loc:organization/maven-2.0/core/boot/classworlds-1.1.jar}
     org.codehaus.classworlds.Launcher
  
    -DdownloadSources=true
    -Dmaven.test.skip=${string_prompt:maven.test.skip:false}  
     clean eclipse:clean eclipse:eclipse install

  The last three lines are configurations for plugins and the actual goals to run. These can be changed if necessary.

  The second to last line is used to have Eclipse prompt for running or skipping tests. Enter 'true' to skip the tests, anything else will run the tests.

• Refresh / Refresh resources upon completion

  Best to activate "The entire workspace" just to be sure all projects are aware of changes.

• Common / Save as Shared file

  Best to select the Root pom project location. The resulting launch file can be put under SCM control.

The EAR project

WTP saves some extra information in the application.xml that would otherwise be generated by the maven-ear-plugin. We do not want to interfere with the maven-ear-plugin, so the maven-eclipse-plugin generates a special application.xml for WTP. This enables you to use the WTP deployer in the server view.

Important: this generated version of the application.xml will NOT be used in the maven build.

The EJB project

WTP automatically uses the ejbModule's source folder, but it is not mandatory. Use the Maven location instead: 'src/main/resources' for the ejb-jar.xml (etc) and 'src/main/java' for the JAVA-beans.

TIP: if WTP can not read your deployment descriptor, check if you included a 'display-name'-tag and specified the xml encoding in the xml file.

The WAR project

Early versions of WTP had some problems when no toplevel directory was used for the webcontent. As of v1.5 this problem is no longer there! This enables using the standard maven directory 'src/main/webapp' as the web-content folder.

The WEB-INF/classes directory can still trigger problems, therefore it is best not to include JAVA classes in a war module. Just put them in a separate JAVA (JAR) module and a lot of undetermined problems disappear.

WTP needs the context root in the war project, but in Maven it is defined in the ear project. As long as the ear project is available in the reactor (as part of the same multi module build) the eclipse plugin will take the context root from the ear project configuration.

The Eclipse MANIFEST files

In Maven the manifest is generated by the maven-jar-plugin from the dependencies just before packaging, but WTP needs them to run. The maven-eclipse-plugin will generate a manifest that is available only to Eclipse (located at 'target/generated-resources/eclipse/META-INF/MANIFEST.MF'), meaning that it will be ignored in the normal maven build.

Deploying with WTP

When you followed all directions described here, there should be no problem to deploy your EARs using the WTP tools for your application server. So there is no need to start a maven build after every change.

Finally

The configuration of the maven-eclipse-plugin used in this description is:

  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-eclipse-plugin</artifactId>
    <version>2.12.1</version>
    <configuration>
      <projectNameTemplate>[artifactId]-[version]</projectNameTemplate>
      <wtpmanifest>true</wtpmanifest>
      <wtpapplicationxml>true</wtpapplicationxml>
      <wtpversion>2.0</wtpversion>
      <manifest>${basedir}/src/main/resources/META-INF/MANIFEST.MF</manifest>
    </configuration>
  </plugin>