eclipse containers for fun and profit

given a multi module project in eclipse, where project X depends on project Y,
when I close project Y,
I want project X to depend on a jar of project Y.

eclipse classpath containers are a mechanism for dynamic late binding of classpath elements.

ibm has a tutorial that requires you to register on their site. m2eclipse does the whole thing for maven projects, but also 99 other things, most of which involve running random maven tasks when your trying to write code.

despite all the static methods and integers enumerations, eclipse makes the whole thing easy; including creating your own plugin and publishing an update-site for it.

the heart of the class path container is the is the IClasspathContainer. The getClasspathEntries() method returns whatever is relevant for that situation. in my case it's either a JavaCore.newProjectEntry() or a JavaCore.newLibraryEntry() depending on whether the referenced project is open or closed at the time. For some reason JavaCore.newVariableEntry() comes out as K_SOURCE which doesn't work for a jar. so I use wrapped the resolved path from newVariableEntry() into a newLibraryEntry to make it a K_BINARY. your type is K_APPLICATION, your path is your unique identifier, and stuff after the slash in the path is parameters for your container. in my case the parameters might be the other projects that this project depends on.

then you need a ClasspathContainerInitializer, which will call JavaCore.setClasspathContainer with a new instance of YourContainer on the dependent projects everytime you open or close one the dependee projects. this then sends an F_CLASSPATH_CHANGED signal to those concerned.

you'll know that a project was opened or closed, because you added an IElementChangedListener with JavaCore.addElementChangedListener().

Your initializer is registered by adding it at the extension point org.eclipse.jdt.core.classpathContainerInitializer. never mind the xml, eclipse will generate it for you.

to allow the addition of containers from the build path configuration menu, eclipse requires a classpathContainerPage. either create a dummy one and register it, or add your container to the classpath file by hand.

Finally, I exported my plugin, and then binary imported the same. This is a nonrecoverable operation that replaces the source code of the plugin with the class files.
*cough*