okhttp3源码分析之RetryAndFollowUpInterceptor

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功能：重试与重定向拦截器。

由于是工厂方法模式，直接调用intercept方法

@Override public Response intercept(Chain chain) throws IOException {
    Request request = chain.request();//获取请求信息
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    Transmitter transmitter = realChain.transmitter();//获取管理器

    int followUpCount = 0;
    Response priorResponse = null;
    //启动无限循环
    while (true) {
      //创建流
      transmitter.prepareToConnect(request);
	  ...
      Response response;
      boolean success = false;
      try {
      	//交给下一个拦截起处理
        response = realChain.proceed(request, transmitter, null);
        success = true;
      } catch (RouteException e) {
        ...
        continue;
      }...

      ...
	  //根据异常状态，返回request对象（判断网络状态404...）
      Request followUp = followUpRequest(response, route);
	  //如果为null（没有异常）关闭请求
      if (followUp == null) {
        ...
        return response;
      }
	  //如果body不是空,并且设置了最多可以传输一次，返回response
      RequestBody followUpBody = followUp.body();
      if (followUpBody != null && followUpBody.isOneShot()) {
        return response;
      }
	  //关闭已有的请求
      closeQuietly(response.body());
      if (transmitter.hasExchange()) {
        exchange.detachWithViolence();
      }
	  //判断重新连接次数
      if (++followUpCount > MAX_FOLLOW_UPS) {
        throw new ProtocolException("Too many follow-up requests: " + followUpCount);
      }
	  //设置参数，重新连接
      request = followUp;
      priorResponse = response;
    }
  }

特点：

1. 通过while(true)死循环来进行重新连接
2. 通过响应码来决定下一次循环的行为是重试、重定向。。。