code: public ImmutableSet<ClassInfo> getAllClassesRecursive(String packageName) {
      checkNotNull(packageName);
      String packagePrefix = packageName + '.';
      ImmutableSet.Builder<ClassInfo> builder = ImmutableSet.builder();
      ImmutableSet<ClassInfo> allClasses = getAllClasses();
      List<String> debugData = Lists.newLinkedList();
      for (ClassInfo classInfo : allClasses) {
        if (classInfo.getName().startsWith(packagePrefix)) {
          builder.add(classInfo);
          debugData.add(classInfo.getResourceName() + "\n");
        }
      }
      return builder.build();
    }
docs: Returns all top level classes whose package name is {@code packageName} or starts with
  {@code packageName} followed by a '.'.