Feign整合Ribbon和Hystrix源碼解析

時間 2019-11-11

標籤 feign 整合 ribbon hystrix 源碼解析简体版

原文原文鏈接

在上篇文章Feign自動裝配中，咱們提到了Feign的自動裝配的原理,以及Feign整合Ribbon和Hystrix的核心在類FeignClientFactoryBean中，那麼本篇文章就來揭開這個類的神祕面紗java

首先，咱們看到這個類實現了FactoryBean這個接口，這個接口的主要做用就是利用getObject()來建立一些實例化過程比較複雜的bean，更多關於這個接口的內容能夠參考這篇文章：Spring擴展點之FactoryBean接口spring

咱們直接來看這個類的getObject方法：app

public Object getObject() throws Exception {
        FeignContext context = applicationContext.getBean(FeignContext.class);
        Feign.Builder builder = feign(context);

        if (!StringUtils.hasText(this.url)) {
            String url;
            if (!this.name.startsWith("http")) {
                url = "http://" + this.name;
            }
            else {
                url = this.name;
            }
            url += cleanPath();
            return loadBalance(builder, context, new HardCodedTarget<>(this.type,
                    this.name, url));
        }
        if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
            this.url = "http://" + this.url;
        }
        String url = this.url + cleanPath();
        Client client = getOptional(context, Client.class);
        if (client != null) {
            if (client instanceof LoadBalancerFeignClient) {
                // not lod balancing because we have a url,
                // but ribbon is on the classpath, so unwrap
                client = ((LoadBalancerFeignClient)client).getDelegate();
            }
            builder.client(client);
        }
        Targeter targeter = get(context, Targeter.class);
        return targeter.target(this, builder, context, new HardCodedTarget<>(
                this.type, this.name, url));
    }

獲取bean:FeignContext，這個bean上篇文章已經說過了。裏面包含了各個Feign客戶端的配置

2. 構建Feign.Builder

設置編解碼器負載均衡

protected Feign.Builder feign(FeignContext context) {
        FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
        Logger logger = loggerFactory.create(this.type);

        Feign.Builder builder = get(context, Feign.Builder.class)
                .logger(logger)
                .encoder(get(context, Encoder.class))
                .decoder(get(context, Decoder.class))
                .contract(get(context, Contract.class));
        configureFeign(context, builder);

        return builder;
    }

設置日誌、重試策略、錯誤code解析、超時時間、攔截器ide

protected void configureUsingConfiguration(FeignContext context, Feign.Builder builder) {
        Logger.Level level = getOptional(context, Logger.Level.class);
        if (level != null) {
            builder.logLevel(level);
        }
        Retryer retryer = getOptional(context, Retryer.class);
        if (retryer != null) {
            builder.retryer(retryer);
        }
        ErrorDecoder errorDecoder = getOptional(context, ErrorDecoder.class);
        if (errorDecoder != null) {
            builder.errorDecoder(errorDecoder);
        }
        Request.Options options = getOptional(context, Request.Options.class);
        if (options != null) {
            builder.options(options);
        }
        Map<String, RequestInterceptor> requestInterceptors = context.getInstances(
                this.name, RequestInterceptor.class);
        if (requestInterceptors != null) {
            builder.requestInterceptors(requestInterceptors.values());
        }

        if (decode404) {
            builder.decode404();
        }
    }

判斷Feign是否指定url屬性，正常狀況下是沒有指定url的，因此會添加一個http://前綴

4. 獲取代理

protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
                            HardCodedTarget<T> target) {

    Client client = getOptional(context, Client.class);
    if (client != null) {
        builder.client(client);
        Targeter targeter = get(context, Targeter.class);

        return targeter.target(this, builder, context, target);
    }

    throw new IllegalStateException(
                "No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?");
}

首先獲取Client的實現類，這個實現類是LoadBalancerFeignClient,這個類裏融合了Ribbon的相關內容。而後將Client包裝到Feign.Builder中，接着獲取Targeter，這裏咱們存在Hystrix環境，因此Targeter的實現類爲HystrixTargeterui

public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context,
                        Target.HardCodedTarget<T> target) {
        if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {
            return feign.target(target);
        }
        feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder) feign;
        SetterFactory setterFactory = getOptional(factory.getName(), context,
            SetterFactory.class);
        if (setterFactory != null) {
            builder.setterFactory(setterFactory);
        }
        Class<?> fallback = factory.getFallback();
        if (fallback != void.class) {
            return targetWithFallback(factory.getName(), context, target, builder, fallback);
        }
        Class<?> fallbackFactory = factory.getFallbackFactory();
        if (fallbackFactory != void.class) {
            return targetWithFallbackFactory(factory.getName(), context, target, builder, fallbackFactory);
        }

        return feign.target(target);
    }

接着以Feign客戶端設置了fallback爲例this

private <T> T targetWithFallback(String feignClientName, FeignContext context,Target.HardCodedTarget<T> target,HystrixFeign.Builder builder, Class<?> fallback) {
        T fallbackInstance = getFromContext("fallback", feignClientName, context, fallback, target.type());
        return builder.target(target, fallbackInstance);
    }

接着就是這個代理的建立，如今這個代理中包含了Ribbon和Hystrix。而這個代理類的實現類是HystrixInvocationHandlerurl

public Object invoke(final Object proxy, final Method method, final Object[] args)
      throws Throwable {
    // early exit if the invoked method is from java.lang.Object
    // code is the same as ReflectiveFeign.FeignInvocationHandler
    if ("equals".equals(method.getName())) {
      try {
        Object otherHandler =
            args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
        return equals(otherHandler);
      } catch (IllegalArgumentException e) {
        return false;
      }
    } else if ("hashCode".equals(method.getName())) {
      return hashCode();
    } else if ("toString".equals(method.getName())) {
      return toString();
    }

    HystrixCommand<Object> hystrixCommand = new HystrixCommand<Object>(setterMethodMap.get(method)) {
      @Override
      protected Object run() throws Exception {
        try {
          return HystrixInvocationHandler.this.dispatch.get(method).invoke(args);
        } catch (Exception e) {
          throw e;
        } catch (Throwable t) {
          throw (Error) t;
        }
      }

      @Override
      protected Object getFallback() {
        if (fallbackFactory == null) {
          return super.getFallback();
        }
        try {
          Object fallback = fallbackFactory.create(getExecutionException());
          Object result = fallbackMethodMap.get(method).invoke(fallback, args);
          if (isReturnsHystrixCommand(method)) {
            return ((HystrixCommand) result).execute();
          } else if (isReturnsObservable(method)) {
            // Create a cold Observable
            return ((Observable) result).toBlocking().first();
          } else if (isReturnsSingle(method)) {
            // Create a cold Observable as a Single
            return ((Single) result).toObservable().toBlocking().first();
          } else if (isReturnsCompletable(method)) {
            ((Completable) result).await();
            return null;
          } else {
            return result;
          }
        } catch (IllegalAccessException e) {
          // shouldn't happen as method is public due to being an interface
          throw new AssertionError(e);
        } catch (InvocationTargetException e) {
          // Exceptions on fallback are tossed by Hystrix
          throw new AssertionError(e.getCause());
        }
      }
    };

    if (isReturnsHystrixCommand(method)) {
      return hystrixCommand;
    } else if (isReturnsObservable(method)) {
      // Create a cold Observable
      return hystrixCommand.toObservable();
    } else if (isReturnsSingle(method)) {
      // Create a cold Observable as a Single
      return hystrixCommand.toObservable().toSingle();
    } else if (isReturnsCompletable(method)) {
      return hystrixCommand.toObservable().toCompletable();
    }
    return hystrixCommand.execute();
  }

這裏就利用到了Hystrix的知識，更多關於Hystrix的內容能夠參考以前的文章spa

接着深刻invoke方法代理

public Object invoke(Object[] argv) throws Throwable {
    RequestTemplate template = buildTemplateFromArgs.create(argv);
    Retryer retryer = this.retryer.clone();
    while (true) {
        try {
            return executeAndDecode(template);
        } catch (RetryableException e) {
            retryer.continueOrPropagate(e);
            if (logLevel != Logger.Level.NONE) {
                logger.logRetry(metadata.configKey(), logLevel);
            }
            continue;
        }
    }
}

這裏構建了請求信息和重試策略，具體請求內容在下面：

Object executeAndDecode(RequestTemplate template) throws Throwable {
    Request request = targetRequest(template);

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

    Response response;
    long start = System.nanoTime();
    try {
      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());
      }
    }
  }

再往下深刻就是Ribbon的負載均衡了，具體內容能夠參考以前的文章