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Multiple Module Projects

Project layout

Due to the workspace idea many Eclipse users are used to a flat layout and therefore want to keep this structure. The following sample shows how to handle maven multiple module projects with Eclipse for both the standard maven hierachical project layout and the flat Eclipse-like layout.

Hierachical project layout

Suppose Eclipse is your favorite SCM client, this step by step example shows how to set up a new mutiple module project.

  1. Set up a new Eclipse workspace called step-by-step and add the M2_REPO classpath variable.
  2. Open the command line shell and change to the newly created workspace directory.
  3. From the command line, create a new maven project using the archetype plugin.
    mvn archetype:create -DgroupId=guide.ide.eclipse -DartifactId=guide-ide-eclipse
  4. Create a new simple project guide-ide-eclipse inside the step-by-step workspace with Eclipse (From the menu bar, select File >New > Project. Select Simple > Project). Eclipse will create a simple .project-file for your guide-ide-eclipse-project and you should be able to see the pom.xml-file.
  5. Delete the src-folder and open the pom.xml-file to change the packaging of your parent project to pom.
  6. From the command line change to the guide-ide-eclipse project directory and create some modules.
    cd guide-ide-eclipse
    mvn archetype:create -DgroupId=guide.ide.eclipse -DartifactId=guide-ide-eclipse-site
    mvn archetype:create -DgroupId=guide.ide.eclipse.core -DartifactId=guide-ide-eclipse-core
    mvn archetype:create -DgroupId=guide.ide.eclipse.module1 -DartifactId=guide-ide-eclipse-module1
  7. Add the newly created modules to your parent pom.
  8. Add the parent to the POMs of the new modules:
  9. Add dependency from module1 to the core-module:
  10. Install the project in your local repository and generate the Eclipse files:
    mvn install
    mvn eclipse:eclipse
  11. Check in your project using the Eclipse team support (select from the context menu Team > Share Project). Note: Do not check in the generated Eclipse files. If you use CVS you should have a .cvsignore-file with the following entries for each module:

    Even the parent project should have this .cvsignore-file. Eclipse will automatically generate a new simple .project-file when you check out the project from the repository.

From now on you have different options to proceed. If you are working on all modules simultanously and you'd rather have Eclipse project dependencies than binary dependencies, you should set up a new workspace and import all projects from step-by-step/guide-ide-eclipse. Note, you have to delete the .project-file of your parent project before. The result is the same as checking out the whole project from the command line, running mvn eclipse:eclipse and finally importing the projects into your Eclipse workspace. In both cases you will be able to synchronize your changes using Eclipse.

In case of large projects with many developers involved, it can be tedious to check out all modules and keep them up to date. Especially if you are only interested in one or two modules. In this case using binary dependencies is much more comfortable. Just check out the modules you want to work on with Eclipse and run mvn eclipse:eclipse for each module (see also Maven as an external tool. Of course, all referenced artifacts must be available from your maven repository.

Flat Project Layout

It is possible to move the parent POM in its own directory on the same level with the referenced modules, thus resulting to a Flat Project Layout.

Using a Flat Project Layout you can checkout and edit the parent POM without checking out the whole project.

  1. Create a new directory under guide-ide-eclipse called guide-ide-eclipse-project and move the parent POM to it.
  2. Change the module references in the parent POM to:

Issue: The Maven Release Plugin does not support the flat structure (MRELEASE-261).