Make IntelliJ aware of links to Java elements in XML files - intellij-idea

Question

I have a custom XML format that links to Java resources. For the sake of simplicity let's assume my XML file would look like this:
<root>
<java-class>my.fully.qualified.class.name</java-class>
</root>
Eventually my references will be somewhat more complicated. It will not contain the fully qualified class name directly and I will need some logic to resolve the correct class, but I want to keep the example as simple as possible here.
Now I want it to be possible to Strg+Click on the element's text and want IntelliJ to carry me to the .java file, just like it is possible in Spring-XML files. In the IDEA Plugin Development FAQ there is a link called "How do I add custom references to Java elements in XML files?" which so much sounds like exactly what I need. Unfortunately it links to a discussion where someone is more or less done implementing something like this, having some minor problems. Nevertheless I understood that I probably need to write an implementation of the interface com.intellij.psi.PsiReference. Googling for "PsiReference" and "IntelliJ" or "IDEA" unfortunately did not bring up any tutorials on how to use it, but I found the class XmlValueReference which sounds useful. Yet again googling for "XmlValueReference" did not turn up anything useful on how to use the class. At least the PSI Cookbook tells me that I can find the Java class by using JavaPsiFacade.findClass(). I'd be thankful for any tutorials, hints and the like, that tell the correct usage.
The above linked discussion mentions that I need to call registry.registerReferenceProvider(XmlTag.class, provider) in order to register my provider once I eventually managed to implement it, but of which type is "registry" and where do I get it from?

Answer 1

First of all, here's a nice tutorial that came up a few days ago, which explains the basics of IntelliJ plugin development (you should take a look at the section Reference Contributor).
You will likely have to define your own PsiReferenceContributor, which will be referenced in your plugin.xml like this:
<psi.referenceContributor implementation="com.yourplugin.YourReferenceContributor"/>
In your reference contributor, there's a method registerReferenceProviders(PsiReferenceRegistrar) where you will be able to call registry.registerReferenceProvider(XmlTag.class, provider).
Finally, in your instance of PsiReferenceProvider, you will have to test the tag name to filter out tags which don't contain class references, then find the right Java class using JavaPsiFacade.findClass().
From my experience, the best place to get help regarding IntelliJ plugin development is JetBrains' forums.