【Feign】Feign源码分析(三): FeignClient请求的过程

FeignClient请求的过程，主要是在发送请求的过程中，整合了Ribbon实现负载均衡，以及从注册中心获取服务列表的，最终响应的过程

一.源码入口 SynchronousMethodHandler.invoke()方法

@Override
  public Object invoke(Object[] argv) throws Throwable {
    //发送http请求的模板类，具备请求方法，协议类型，类似，GET /hello HTTP/1.1 
    RequestTemplate template = buildTemplateFromArgs.create(argv);
    //获取重试器，主要用于在异常时的重试
    Retryer retryer = this.retryer.clone();
    while (true) {
      try {
        //执行请求的核心逻辑
        return executeAndDecode(template);
      } catch (RetryableException e) {
        retryer.continueOrPropagate(e);
        if (logLevel != Logger.Level.NONE) {
          logger.logRetry(metadata.configKey(), logLevel);
        }
        continue;
      }
    }
  }

执行请求的核心逻辑executeAndDecode()

Object executeAndDecode(RequestTemplate template) throws Throwable {
    //将requestTemplate对象转换为request对象 类似  GET http://HELLO-SERVICE/hello，以及执行拦截器相关的逻辑
    Request request = targetRequest(template);

    if (logLevel != Logger.Level.NONE) {
      logger.logRequest(metadata.configKey(), logLevel, request);
    }

    Response response;
    long start = System.nanoTime();
    try {
　　 //这里主要是使用LoadBalanceFeignClient执行execute()方法
      response = client.execute(request, options);
      // ensure the request is set. TODO: remove in Feign 10
      response.toBuilder().request(request).build();
    } catch (IOException e) {
      if (logLevel != Logger.Level.NONE) {
        logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start));
      }
      throw errorExecuting(request, e);
    }
    long elapsedTime = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);

    boolean shouldClose = true;
    try {
      if (logLevel != Logger.Level.NONE) {
        response =
            logger.logAndRebufferResponse(metadata.configKey(), logLevel, response, elapsedTime);
        // ensure the request is set. TODO: remove in Feign 10
        response.toBuilder().request(request).build();
      }
      if (Response.class == metadata.returnType()) {
        if (response.body() == null) {
          return response;
        }
        if (response.body().length() == null ||
                response.body().length() > MAX_RESPONSE_BUFFER_SIZE) {
          shouldClose = false;
          return response;
        }
        // Ensure the response body is disconnected
        byte[] bodyData = Util.toByteArray(response.body().asInputStream());
        return response.toBuilder().body(bodyData).build();
      }
      if (response.status() >= 200 && response.status() < 300) {
        if (void.class == metadata.returnType()) {
          return null;
        } else {
          return decode(response);
        }
      } else if (decode404 && response.status() == 404 && void.class != metadata.returnType()) {
        return decode(response);
      } else {
        throw errorDecoder.decode(metadata.configKey(), response);
      }
    } catch (IOException e) {
      if (logLevel != Logger.Level.NONE) {
        logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime);
      }
      throw errorReading(request, response, e);
    } finally {
      if (shouldClose) {
        ensureClosed(response.body());
      }
    }
  }

client.execute(request, options);执行真实请求

@Override
    public Response execute(Request request, Request.Options options) throws IOException {
        try {
　　　　　　  //获取请求的URI
            URI asUri = URI.create(request.url());
            String clientName = asUri.getHost();
            URI uriWithoutHost = cleanUrl(request.url(), clientName);
            FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(
                    this.delegate, request, uriWithoutHost);
            IClientConfig requestConfig = getClientConfig(options, clientName);
　　　　　　  //lbClient主要是通过服务名，在Ribbon中获取服务名对应的FeignLoadBalance，执行executeWithLoadBalancer()
            return lbClient(clientName).executeWithLoadBalancer(ribbonRequest,
                    requestConfig).toResponse();
        }
        catch (ClientException e) {
            IOException io = findIOException(e);
            if (io != null) {
                throw io;
            }
            throw new RuntimeException(e);
        }
    }

lbClient(clientName) 整合Ribbon，通过服务名获取FeignLoadBalance

public FeignLoadBalancer create(String clientName) {
        //优先从缓存工厂里面获取
        FeignLoadBalancer client = this.cache.get(clientName);
        if(client != null) {
            return client;
        }
        IClientConfig config = this.factory.getClientConfig(clientName);
        ILoadBalancer lb = this.factory.getLoadBalancer(clientName);
        ServerIntrospector serverIntrospector = this.factory.getInstance(clientName, ServerIntrospector.class);
        client = loadBalancedRetryFactory != null ? new RetryableFeignLoadBalancer(lb, config, serverIntrospector,
            loadBalancedRetryFactory) : new FeignLoadBalancer(lb, config, serverIntrospector);
        this.cache.put(clientName, client);
        return client;
    }

executeWithLoadBalancer()方法

public T executeWithLoadBalancer(final S request, final IClientConfig requestConfig) throws ClientException {
        LoadBalancerCommand<T> command = buildLoadBalancerCommand(request, requestConfig);
　　　　 //comand.submit方法就是通过FeignLoadBalancer去获取服务名对应的服务URL
        try {
            return command.submit(
                new ServerOperation<T>() {
                    @Override
                    public Observable<T> call(Server server) {
                        URI finalUri = reconstructURIWithServer(server, request.getUri());
                        S requestForServer = (S) request.replaceUri(finalUri);
                        try {
                            return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
                        } 
                        catch (Exception e) {
                            return Observable.error(e);
                        }
                    }
                })
                .toBlocking()
                .single();
        } catch (Exception e) {
            Throwable t = e.getCause();
            if (t instanceof ClientException) {
                throw (ClientException) t;
            } else {
                throw new ClientException(e);
            }
        }
        
    }