OKHttp 执行拦截器前

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在同步和异步方法中都调用 

getResponseWithInterceptorChain():

Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors()); //由我们能定义的 不是由我们定义成为系统拦截器
    interceptors.add(retryAndFollowUpInterceptor);
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    interceptors.add(new CacheInterceptor(client.internalCache()));
    interceptors.add(new ConnectInterceptor(client));
    if (!forWebSocket) {//默认是false
      interceptors.addAll(client.networkInterceptors()); //由我们能定义的
}
    interceptors.add(new CallServerInterceptor(forWebSocket));
     //创建拦截器链 并调用proceed(...)
    Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

    return chain.proceed(originalRequest);


}

作用:将创建系统拦截器和读取我们定义的拦截器 放入拦截器链中 并执行 proceed(....)

@Override public Response proceed(Request request) throws IOException {
    return proceed(request, streamAllocation, httpCodec, connection); //重载方法
  }

  public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
      RealConnection connection) throws IOException {
    if (index >= interceptors.size()) throw new AssertionError();

    calls++;

    // If we already have a stream, confirm that the incoming request will use it.
    if (this.httpCodec != null && !this.connection.supportsUrl(request.url())) {
      throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
          + " must retain the same host and port");
    }

    // If we already have a stream, confirm that this is the only call to chain.proceed().
    if (this.httpCodec != null && calls > 1) {
      throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
          + " must call proceed() exactly once");
    }

    // Call the next interceptor in the chain.
      // index+1 下次进来时取得下一个拦截器
 RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
        connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
        writeTimeout);
     //取出拦截器并执行intercept(...)方法
   Interceptor interceptor = interceptors.get(index);
    Response response = interceptor.intercept(next);

    // Confirm that the next interceptor made its required call to chain.proceed().
   确保每个拦截器都调用了proceed
 if (httpCodec != null && index + 1 < interceptors.size() && next.calls != 1) {
      throw new IllegalStateException("network interceptor " + interceptor
          + " must call proceed() exactly once");
    }

    // Confirm that the intercepted response isn't null.
    if (response == null) {
      throw new NullPointerException("interceptor " + interceptor + " returned null");
    }

    if (response.body() == null) {
      throw new IllegalStateException(
          "interceptor " + interceptor + " returned a response with no body");
    }

    return response;
  }

作用: 创建新拦截器链执行 拦截器intercept方法

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