拦截器分类

应用程序拦截器
网络拦截器

源码分析

public Response execute() throws IOException {
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    eventListener.callStart(this);
    try {
      client.dispatcher().executed(this);
      Response result = getResponseWithInterceptorChain();  //位置 1
      if (result == null) throw new IOException("Canceled");
      return result;
    } catch (IOException e) {
      eventListener.callFailed(this, e);
      throw e;
    } finally {
      client.dispatcher().finished(this);
    }
  }

Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    //添加用户自定义拦截器
    interceptors.addAll(client.interceptors());
    //重试和失败重定向拦截器
    interceptors.add(retryAndFollowUpInterceptor);
    //桥接拦截器，处理一些必须的请求头信息的拦截器
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    //缓存拦截器
    interceptors.add(new CacheInterceptor(client.internalCache()));
    //连接拦截器：建立可用的连接，是CallServerInterceptor的基本
    interceptors.add(new ConnectInterceptor(client));
    if (!forWebSocket) {
      interceptors.addAll(client.networkInterceptors());
    }
    //将http请求写进io流当中，并且从io流中读取response
    interceptors.add(new CallServerInterceptor(forWebSocket));
 
    //初始化 RealInterceptorChain
    Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());
 
    return chain.proceed(originalRequest);
  }

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.
  （1）调用下一个拦截器
  RealInterceptorChain next = new RealInterceptorChain(
      interceptors, streamAllocation, httpCodec, connection, index + 1, request);
  Interceptor interceptor = interceptors.get(index);
  Response response = interceptor.intercept(next);

  // Confirm that the next interceptor made its required call to chain.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");
  }

  return response;
}

调用流程图

Okhttp 拦截器

拦截器分类

源码分析

每个拦截器的作用：

参考: