public static List<Class<?>> getClassesOfPackage(String packageName) {
    InputStream stream = ClassLoader.getSystemClassLoader().getResourceAsStream(packageName.replaceAll("[.]", "/"));
    if (stream == null) return new ArrayList<>();
    BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
    return reader.lines()
         .filter(line -> line.endsWith(".class"))
         .map(line -> {
             try {
                return Class.forName(packageName + "." + line.substring(0, line.lastIndexOf('.')));
             } catch (ClassNotFoundException e) {
                e.printStackTrace();
             }
             return null;
         })
         .collect(Collectors.toList());
}