code: public Class findImplementation(Class interfase) throws IOException, ClassNotFoundException {
          String className = findString(interfase.getName());
          Class impl = classLoader.loadClass(className);
          if (!interfase.isAssignableFrom(impl)) {
              throw new ClassCastException("Class not of type: " + interfase.getName());
          }
          return impl;
      }
docs: Assumes the class specified points to a file in the classpath that contains
  the name of a class that implements or is a subclass of the specfied class.
  <p/>
  Any class that cannot be loaded will be cause an exception to be thrown.
  <p/>
  Example classpath:
  <p/>
  META-INF/java.io.InputStream    # contains the classname org.acme.AcmeInputStream
  META-INF/java.io.OutputStream
  <p/>
  ResourceFinder finder = new ResourceFinder("META-INF/");
  Class clazz = finder.findImplementation(java.io.InputStream.class);
  clazz.getName();  // returns "org.acme.AcmeInputStream"
  
  @param interfase a superclass or interface
  @return
  @throws IOException            if the URL cannot be read
  @throws ClassNotFoundException if the class found is not loadable
  @throws ClassCastException     if the class found is not assignable to the specified superclass or interface