Reflections from Maven Mojo

Question

I'd like to use Google Reflections to scan classes from the compiled project from my Maven plugin. But plugins by default don't see the compiled classes of the project. From Maven 3 documentation I read:

Plugins that need to load classes from the compile/runtime/test class path of a project need to create a custom URLClassLoader in combination with the mojo annotation @requiresDependencyResolution.

Which is a bit vague to say the least. Basically I would need a reference to a classloader that loads the compiled project classes. How do I get that?

EDIT:

Ok, the @Mojo annotation has requiresDependencyResolution parameter, so that's easy but still need the correct way to build a classloader.

I think "compile (...) class path of a project" really still refers to its dependencies, and you're down to: "a custom class loader needs to be created". — Sander Verhagen, Nov 01 '13 at 07:22
I don't understand what the blocker is here. A Google for custom classloader will provide plenty of examples. If all else fails you can also take a peek at the source of an existing Maven plugin that works on project classes and borrow some bits and bobs. — Gimby, Nov 01 '13 at 09:53

score 12 · Accepted Answer · edited Jan 18 '16 at 17:06

@Component
private MavenProject project;

@SuppressWarnings("unchecked")
@Override
public void execute() throws MojoExecutionException {
    List<String> classpathElements = null;
    try {
        classpathElements = project.getCompileClasspathElements();
        List<URL> projectClasspathList = new ArrayList<URL>();
        for (String element : classpathElements) {
            try {
                projectClasspathList.add(new File(element).toURI().toURL());
            } catch (MalformedURLException e) {
                throw new MojoExecutionException(element + " is an invalid classpath element", e);
            }
        }

        URLClassLoader loader = new URLClassLoader(projectClasspathList.toArray(new URL[0]));
        // ... and now you can pass the above classloader to Reflections

    } catch (ClassNotFoundException e) {
        throw new MojoExecutionException(e.getMessage());
    } catch (DependencyResolutionRequiredException e) {
        new MojoExecutionException("Dependency resolution failed", e);
    }
}

If You do URLClassLoader loader = new URLClassLoader(projectClasspathList.toArray(new URL[0]), Thread.currentThread().getContextClassLoader()); Then the classes You load as plugin dependencies will be instances of the same, that would be returned by Reflections — maslan, May 25 '16 at 07:36
Thanks! I had ClassNotFoundExceptions from within my plugin logic, using Class names returned by `Reflections#getAllTypes()` until I `Class.forName(type, true, loader)` where loader is your loader — juanmf, Aug 02 '16 at 11:07

Reflections from Maven Mojo

1 Answers1