code: public static Object invokeMethod(final Object obj, final String methodName, final Class<?>[] parameterTypes,
  			final Object[] args) {
  		Method method = getAccessibleMethod(obj, methodName, parameterTypes);
  		if (method == null) {
  			throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + obj + "]");
  		}
  
  		try {
  			return method.invoke(obj, args);
  		} catch (Exception e) {
  			throw convertReflectionExceptionToUnchecked(e);
  		}
  	}
docs: 直接调用对象方法, 无视private/protected修饰符.
  用于一次性调用的情况.