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javareflectionannotationsaopguice

Java - Register all classes annotated with @MyAnnotation

I have an annotation @MyAnnotation and I can annotate any type (class) with it. Then I have a class called AnnotatedClassRegister and I would like it to register all classes annotated with @MyAnnotation so I can access them later. And I'd like to register these classes automatically upon creation of the AnnotatedClassRegister if possible, and most importantly before the annotated classes are instantiated.

I have AspectJ and Guice at my disposal. The only solution I came up with so far is to use Guice to inject a singleton instance of the AnnotatedClassRegister to an aspect, which searches for all classes annotated with @MyAnnotation and it adds the code needed to register such class in its constructor. The downside of this solution is that I need to instantiate every annotated class in order for the code added by AOP to be actually run, therefore I cannot utilize lazy instantiation of these classes.

Simplified pseudo-code example of my solution:

// This is the class where annotated types are registered
public class AnnotatedClassRegister {
    public void registerClass(Class<?> clz) {
        ...
    }
}

// This is the aspect which adds registration code to constructors of annotated
// classes
public aspect AutomaticRegistrationAspect {

    @Inject
    AnnotatedClassRegister register;

    pointcutWhichPicksConstructorsOfAnnotatedClasses(Object annotatedType) : 
            execution(/* Pointcut definition */) && args(this)

    after(Object annotatedType) :
            pointcutWhichPicksConstructorsOfAnnotatedClasses(annotatedType) {

        // registering the class of object whose constructor was picked 
        // by the pointcut
        register.registerClass(annotatedType.getClass())
    }
}

What approach should I use to address this problem? Is there any simple way to get all such annotated classes in classpath via reflection so I wouldn't need to use AOP at all? Or any other solution?

Any ideas are much appreciated, thanks!

Solution

  • It's possible:

    1. Get all paths in a classpath. Parse System.getProperties().getProperty("java.class.path", null) to get all paths.

    2. Use ClassLoader.getResources(path) to get all resources and check for classes: http://snippets.dzone.com/posts/show/4831