Why doesn't reflection work when a class returns Lambdas

Question

I have encountered a somewhat strange behaviour. I use annotations to mark certain classes with a particular purpose, and then I use org.reflections library to find all the

Answer 1

You may perform the lookup without any third-party code as follows:

private static  Set> getAnnotated(
        Class context, Class anno) throws IOException, URISyntaxException {

    URI clURI = context.getResource(context.getSimpleName()+".class").toURI();
    if(!clURI.getScheme().equals("file")) try {
        FileSystems.getFileSystem(clURI);
    } catch(FileSystemNotFoundException ex) {
        FileSystems.newFileSystem(clURI, Collections.emptyMap());
    }
    String pkg=context.getPackage().getName();
    return Files.list(Paths.get(clURI).getParent())
        .map(p->p.getFileName().toString())
        .filter(s->s.endsWith(".class"))
        .map(s->s.substring(0, s.length()-6))
        .map(s-> { try {
            return context.getClassLoader().loadClass(pkg+'.'+s);
          } catch(ClassNotFoundException ex) { return null; } })
        .filter(c -> c!=null && c.isAnnotationPresent(anno))
        .collect(Collectors.toSet());
}

The advantage of Path over good old File is that it abstracts over the filesystem (storage) and thus can be used to list package members even if the Class is stored in a jar file (or any other kind of class storage for which a FileSystemProvider exists).

You may use it as

Set> clazzes  = getAnnotated(context, MyAnnotation.class);

where context is a Class within the package for which you want to get a annotated classes.