code: private static Method getDeclaredMethods(Class<?> clazz, String methodName) {
          Method[] methods = clazz.getDeclaredMethods();
          for (Method method : methods) {
              if (method.getName().equals(methodName)) {
                  return method;
              }
          }
          throw new IllegalArgumentException("方法" + methodName + "不存在！");
      }
docs: 获取指定的方法