code: public boolean checkService(String serviceName, String methodName) {
          Invoker invoker = invokerMap.get(serviceName);
          return invoker instanceof ProviderProxyInvoker && getMethod(serviceName, methodName) != null;
      }
docs: Check service exists
  
  @param serviceName Service Name
  @param methodName  Method name
  @return if service and method exists, return true.