code: @Override
      public MethodDescriptor<String> getServiceDescriptor(String key) {
          Preconditions.checkNotNull(key, "Key cannot be null");
          return serviceRegistry.getServiceDescriptorByKey(key);
      }
docs: 根据服务标示获取服务方法的描述
  
  @param key
  @return 服务方法的描述
  @see com.baidu.beidou.navi.server.locator.ServiceLocator#getServiceDescriptor(java.lang.Object)