OkHttp

OkHttp

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OkHttp 请求处理过程：

1、通过 OkhttpClient 创立一个 client，组装 Request，通过 client.newCall(request).execute() 发起同步请求，或 client.newCall(request).enqueue(Callback) 发起异步请求。
2、OkHttp 通过 Dispatcher 对所有的 Call（RealCall 实现）进行统一管理，并通过 execute() 及 enqueue() 方法对同步或者异步请求进行执行；
3、execute() 及 enqueue() 这两个方法会最终调用 RealCall 中的 getResponseWithInterceptorChain() 方法，从阻拦器链中获取返回结果
4、OkHttp 拦截器链中，依次通 过ApplicationInterceptor（应用拦截器）、RetryAndFollowUpInterceptor（重定向阻拦器）、BridgeInterceptor（桥接阻拦器）、CacheInterceptor（缓存阻拦器）、ConnectInterceptor（连接阻拦器）、NetwrokInterceptor（网络拦截器）、CallServerInterceptor（请求阻拦器）对请求依次处理。

final class RealCall implements Call {
  @Override public Response execute() throws IOException {
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    transmitter.timeoutEnter();
    transmitter.callStart();
    try {
      client.dispatcher().executed(this);
      return getResponseWithInterceptorChain();
    } finally {
      client.dispatcher().finished(this);
    }
  }

  Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());
    interceptors.add(new RetryAndFollowUpInterceptor(client));
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    interceptors.add(new CacheInterceptor(client.internalCache()));
    interceptors.add(new ConnectInterceptor(client));
    if (!forWebSocket) {
      interceptors.addAll(client.networkInterceptors());
    }
    interceptors.add(new CallServerInterceptor(forWebSocket));

    Interceptor.Chain chain = new RealInterceptorChain(interceptors, transmitter, null, 0,
        originalRequest, this, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

    boolean calledNoMoreExchanges = false;
    try {
      Response response = chain.proceed(originalRequest);
      if (transmitter.isCanceled()) {
        closeQuietly(response);
        throw new IOException("Canceled");
      }
      return response;
    } catch (IOException e) {
      calledNoMoreExchanges = true;
      throw transmitter.noMoreExchanges(e);
    } finally {
      if (!calledNoMoreExchanges) {
        transmitter.noMoreExchanges(null);
      }
    }
  }
}

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