okhttp3 源码分析

总体流程

下面的流程图是由上面的文章抄来的（自己画的图，用的visio）
整个流程是，通过OkHttpClient将构建的Request转换为Call，然后在RealCall中进行异步或同步任务，最后通过一些的拦截器interceptor发出网络请求和得到返回的response。
将流程大概是这么个流程，大家可以有个大概的印象，继续向下看：

为了让大家有更深的印象，我准备追踪一个GET网络请求的具体流程，来介绍在源码中发生了什么。

GET请求过程

这是利用OkHttp写一个Get请求步骤，这里是一个同步的请求,异步的下面也会说：

   //HTTP GET    public String get(String url) throws IOException {        //新建OKHttpClient客户端        OkHttpClient client = new OkHttpClient();        //新建一个Request对象        Request request = new Request.Builder()                .url(url)                .build();        //Response为OKHttp中的响应        Response response = client.newCall(request).execute();        if (response.isSuccessful()) {            return response.body().string();        }else{            throw new IOException("Unexpected code " + response);        }    }

OKHttpClient：流程的总控制者

OkHttpClient的类设计图

使用OkHttp的时候我们都会创建一个OkHttpClient对象:
OkHttpClient client = new OkHttpClient();
这是做什么的呢？看下builder里面的参数：

     final Dispatcher dispatcher;  //分发器    final Proxy proxy;  //代理    final List<Protocol> protocols; //协议    final List<ConnectionSpec> connectionSpecs; //传输层版本和连接协议    final List<Interceptor> interceptors; //拦截器    final List<Interceptor> networkInterceptors; //网络拦截器    final ProxySelector proxySelector; //代理选择    final CookieJar cookieJar; //cookie    final Cache cache; //缓存    final InternalCache internalCache;  //内部缓存    final SocketFactory socketFactory;  //socket 工厂    final SSLSocketFactory sslSocketFactory; //安全套接层socket 工厂，用于HTTPS    final CertificateChainCleaner certificateChainCleaner; // 验证确认响应证书 适用 HTTPS 请求连接的主机名。    final HostnameVerifier hostnameVerifier;    //  主机名字确认    final CertificatePinner certificatePinner;  //  证书链    final Authenticator proxyAuthenticator;     //代理身份验证    final Authenticator authenticator;      // 本地身份验证    final ConnectionPool connectionPool;    //连接池,复用连接    final Dns dns;  //域名    final boolean followSslRedirects;  //安全套接层重定向    final boolean followRedirects;  //本地重定向    final boolean retryOnConnectionFailure; //重试连接失败    final int connectTimeout;    //连接超时    final int readTimeout; //read 超时    final int writeTimeout; //write 超时

在这些声明的对象中可以看出来，几乎所有用到的类都和OkHttpClient有关系。事实上，你能够通过它来设置改变一些参数，因为他是通过建造者模式实现的，因此你可以通过builder()来设置。如果不进行设置，在Builder中就会使用默认的设置：

            dispatcher = new Dispatcher();            protocols = DEFAULT_PROTOCOLS;            connectionSpecs = DEFAULT_CONNECTION_SPECS;            proxySelector = ProxySelector.getDefault();            cookieJar = CookieJar.NO_COOKIES;            socketFactory = SocketFactory.getDefault();            hostnameVerifier = OkHostnameVerifier.INSTANCE;            certificatePinner = CertificatePinner.DEFAULT;            proxyAuthenticator = Authenticator.NONE;            authenticator = Authenticator.NONE;            connectionPool = new ConnectionPool();            dns = Dns.SYSTEM;            followSslRedirects = true;            followRedirects = true;            retryOnConnectionFailure = true;            connectTimeout = 10_000;            readTimeout = 10_000;            writeTimeout = 10_000;

看到这，如果你还不明白的话，也没关系，在OkHttp中只是设置用的的各个东西。真正的流程要从里面的newCall()方法中说起：

       /**        *  Prepares the {@code request} to be executed at some point in the future.        *  准备将要被执行的request        */        @Override        public Call newCall(Request request) {            return new RealCall(this, request);        }

当通过建造者模式创建了Request之后（这个没什么好说），紧接着就通过下面的代码来获得Response
大家还记得上面做GET请求时的这句代码吧：
Response response = client.newCall(request).execute();这就代码就开启了整个GET请求的流程：

RealCall：真正的请求执行者。

先看一下他的构造方法：

protected RealCall(OkHttpClient client, Request originalRequest) {      this.client = client;        this.originalRequest = originalRequest;        this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client);}

可以看到他传过来一个OkHttpClient对象和一个originalRequest（我们创建的Request）。
接下来看它的execute()方法：

 @Override    public Response execute() throws IOException {        synchronized (this) {            if (executed) throw new IllegalStateException("Already Executed"); //(1)            executed = true;        }        try {            client.dispatcher.executed(this);//(2)            Response result = getResponseWithInterceptorChain();//(3)            if (result == null) throw new IOException("Canceled");            return result;        }finally {            client.dispatcher.finished(this);//(4)        }    }

1. 检查这个 call是否已经被执行了，每个 call 只能被执行一次，如果想要一个完全一样的 call，可以利用 all#clone 方法进行克隆。
2. 利用 client.dispatcher().executed(this) 来进行实际执行，dispatcher 是刚才看到的 OkHttpClient.Builder 的成员之一，它的文档说自己是异步 HTTP请求的执行策略，现在看来，同步请求它也有掺和。
3. 调用 getResponseWithInterceptorChain() 函数获取 HTTP 返回结果，从函数名可以看出，这一步还会进行一系列“拦截”操作。

4. 最后还要通知 dispatcher 自己已经执行完毕。
   dispatcher 这里我们不过度关注，在同步执行的流程中，涉及到 dispatcher 的内容只不过是告知它我们的执行状态，比如开始执行了（调用 executed），比如执行完毕了（调用 finished），在异步执行流程中它会有更多的参与。
   真正发出网络请求，解析返回结果的，还是 getResponseWithInterceptorChain：

   //拦截器的责任链。 private Response getResponseWithInterceptorChain() throws IOException {     // Build a full stack of interceptors.     List<Interceptor> interceptors = new ArrayList<>();     interceptors.addAll(client.interceptors());     //(1)     interceptors.add(retryAndFollowUpInterceptor);    //(2)     interceptors.add(new BridgeInterceptor(client.cookieJar()));    //(3)     interceptors.add(new CacheInterceptor(client.internalCache()));    //(4)     interceptors.add(new ConnectInterceptor(client));    //(5)     if (!retryAndFollowUpInterceptor.isForWebSocket()) {         interceptors.addAll(client.networkInterceptors());    //(6)     }     interceptors.add(new CallServerInterceptor(             retryAndFollowUpInterceptor.isForWebSocket()));     //(7)     Interceptor.Chain chain = new RealInterceptorChain(             interceptors, null, null, null, 0, originalRequest);     return chain.proceed(originalRequest); //  <<=========开始链式调用 }

1. 在配置 OkHttpClient 时设置的 interceptors；
2. 负责失败重试以及重定向的 RetryAndFollowUpInterceptor；
3. 负责把用户构造的请求转换为发送到服务器的请求、把服务器返回的响应转换为用户友好的响应的 BridgeInterceptor；
4. 负责读取缓存直接返回、更新缓存的 CacheInterceptor；
5. 负责和服务器建立连接的 ConnectInterceptor；
6. 配置 OkHttpClient 时设置的 networkInterceptors；
7. 负责向服务器发送请求数据、从服务器读取响应数据的 CallServerInterceptor。
8. 在return chain.proceed(originalRequest);中开启链式调用：

RealInterceptorChain

 public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,      Connection 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.    //如果我们已经有一个stream。确定即将到来的request会使用它    if (this.httpCodec != null && !sameConnection(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().    //如果我们已经有一个stream， 确定chain.proceed()唯一的call    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.    //调用链的下一个拦截器    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;  }`

代码很多，但是主要是进行一些判断，主要的代码在这：

// Call the next interceptor in the chain.    //调用链的下一个拦截器    RealInterceptorChain next = new RealInterceptorChain(        interceptors, streamAllocation, httpCodec, connection, index + 1, request);    //(1)    Interceptor interceptor = interceptors.get(index);     //(2)    Response response = interceptor.intercept(next);    //(3)

1. 实例化下一个拦截器对应的RealIterceptorChain对象，这个对象会在传递给当前的拦截器
2. 得到当前的拦截器：interceptors是存放拦截器的ArryList
3. 调用当前拦截器的intercept()方法，并将下一个拦截器的RealIterceptorChain对象传递下去
   除了在client中自己设置的interceptor,第一个调用的就是retryAndFollowUpInterceptor

   RetryAndFollowUpInterceptor:负责失败重试以及重定向

   直接上代码

@Override public Response intercept(Chain chain) throws IOException {        Request request = chain.request();        streamAllocation = new StreamAllocation(                client.connectionPool(), createAddress(request.url()));        int followUpCount = 0;        Response priorResponse = null;        while (true) {            if (canceled) {                streamAllocation.release();                throw new IOException("Canceled");            }            Response response = null;            boolean releaseConnection = true;            try {                response = ((RealInterceptorChain) chain).proceed(request, streamAllocation, null, null);    //(1)                releaseConnection = false;            } catch (RouteException e) {                // The attempt to connect via a route failed. The request will not have been sent.                //通过路线连接失败，请求将不会再发送                if (!recover(e.getLastConnectException(), true, request)) throw e.getLastConnectException();                releaseConnection = false;                continue;            } catch (IOException e) {                // An attempt to communicate with a server failed. The request may have been sent.                // 与服务器尝试通信失败，请求不会再发送。                if (!recover(e, false, request)) throw e;                releaseConnection = false;                continue;            } finally {                // We're throwing an unchecked exception. Release any resources.                //抛出未检查的异常，释放资源                if (releaseConnection) {                    streamAllocation.streamFailed(null);                    streamAllocation.release();                }            }            // Attach the prior response if it exists. Such responses never have a body.            // 附加上先前存在的response。这样的response从来没有body            // TODO: 2016/8/23 这里没赋值，岂不是一直为空？            if (priorResponse != null) { //  (2)                response = response.newBuilder()                        .priorResponse(priorResponse.newBuilder()                                .body(null)                                .build())                        .build();            }            Request followUp = followUpRequest(response); //判断状态码 (3)            if (followUp == null){                if (!forWebSocket) {                    streamAllocation.release();                }                return response;            }            closeQuietly(response.body());            if (++followUpCount > MAX_FOLLOW_UPS) {                streamAllocation.release();                throw new ProtocolException("Too many follow-up requests: " + followUpCount);            }            if (followUp.body() instanceof UnrepeatableRequestBody) {                throw new HttpRetryException("Cannot retry streamed HTTP body", response.code());            }            if (!sameConnection(response, followUp.url())) {                streamAllocation.release();                streamAllocation = new StreamAllocation(                        client.connectionPool(), createAddress(followUp.url()));            } else if (streamAllocation.codec() != null) {                throw new IllegalStateException("Closing the body of " + response                        + " didn't close its backing stream. Bad interceptor?");            }            request = followUp;            priorResponse = response;        }    }

1. 这里是最关键的代码，可以看出在response = ((RealInterceptorChain) chain).proceed(request, streamAllocation, null, null);中直接调用了下一个拦截器，然后捕获可能的异常来进行操作
2. 这里没看太懂，有点坑，以后补
3. 这里对于返回的response的状态码进行判断，然后进行处理

BridgeInterceptor：

负责把用户构造的请求转换为发送到服务器的请求、把服务器返回的响应转换为用户友好的响应的 。

@Override public Response intercept(Chain chain) throws IOException {    Request userRequest = chain.request();    Request.Builder requestBuilder = userRequest.newBuilder();    //检查request。将用户的request转换为发送到server的请求    RequestBody body = userRequest.body();     //(1)    if (body != null) {      MediaType contentType = body.contentType();      if (contentType != null) {        requestBuilder.header("Content-Type", contentType.toString());      }      long contentLength = body.contentLength();      if (contentLength != -1) {        requestBuilder.header("Content-Length", Long.toString(contentLength));        requestBuilder.removeHeader("Transfer-Encoding");      } else {        requestBuilder.header("Transfer-Encoding", "chunked");        requestBuilder.removeHeader("Content-Length");      }    }    if (userRequest.header("Host") == null) {      requestBuilder.header("Host", hostHeader(userRequest.url(), false));    }    if (userRequest.header("Connection") == null) {      requestBuilder.header("Connection", "Keep-Alive");    }      // If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing    // the transfer stream.    //GZIP压缩    boolean transparentGzip = false;    if (userRequest.header("Accept-Encoding") == null) {      transparentGzip = true;      requestBuilder.header("Accept-Encoding", "gzip");    }    List<Cookie> cookies = cookieJar.loadForRequest(userRequest.url());    if (!cookies.isEmpty()) {      requestBuilder.header("Cookie", cookieHeader(cookies));    }    if (userRequest.header("User-Agent") == null) {      requestBuilder.header("User-Agent", Version.userAgent());    }    Response networkResponse = chain.proceed(requestBuilder.build());   //(2)    HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers()); //(3)    Response.Builder responseBuilder = networkResponse.newBuilder()        .request(userRequest);    if (transparentGzip        && "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))        && HttpHeaders.hasBody(networkResponse)) {      GzipSource responseBody = new GzipSource(networkResponse.body().source());      Headers strippedHeaders = networkResponse.headers().newBuilder()          .removeAll("Content-Encoding")          .removeAll("Content-Length")          .build();      responseBuilder.headers(strippedHeaders);      responseBuilder.body(new RealResponseBody(strippedHeaders, Okio.buffer(responseBody)));    }    return responseBuilder.build();  }

1. 在（1）和（2）之间，BridgeInterceptor对于request的格式进行检查，让构建了一个新的request
2. 调用下一个interceptor来得到response
3. （3）下面就是对得到的response进行一些判断操作，最后将结果返回。
4. 主要利用while(true) 一直重试

@Override public Response intercept(Chain chain) throws IOException {    Response cacheCandidate = cache != null        //=============(1)        ? cache.get(chain.request()) //通过request得到缓存        : null;    long now = System.currentTimeMillis();    CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get(); //根据request来得到缓存策略===========(2)    Request networkRequest = strategy.networkRequest;    Response cacheResponse = strategy.cacheResponse;    if (cache != null) {      cache.trackResponse(strategy);    }    if (cacheCandidate != null && cacheResponse == null) { //存在缓存的response，但是不允许缓存      closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it. 缓存不适合，关闭    }    // If we're forbidden from using the network and the cache is insufficient, fail.      //如果我们禁止使用网络，且缓存为null，失败    if (networkRequest == null && cacheResponse == null) {      return new Response.Builder()          .request(chain.request())          .protocol(Protocol.HTTP_1_1)          .code(504)          .message("Unsatisfiable Request (only-if-cached)")          .body(EMPTY_BODY)          .sentRequestAtMillis(-1L)          .receivedResponseAtMillis(System.currentTimeMillis())          .build();    }    // If we don't need the network, we're done.    if (networkRequest == null) {  //没有网络请求，跳过网络，返回缓存      return cacheResponse.newBuilder()          .cacheResponse(stripBody(cacheResponse))          .build();    }    Response networkResponse = null;    try {      networkResponse = chain.proceed(networkRequest);//网络请求拦截器    //======(3)    } finally {      // If we're crashing on I/O or otherwise, don't leak the cache body.        //如果我们因为I/O或其他原因崩溃，不要泄漏缓存体      if (networkResponse == null && cacheCandidate != null) {        closeQuietly(cacheCandidate.body());      }    }    // If we have a cache response too, then we're doing a conditional get.========(4)      //如果我们有一个缓存的response，然后我们正在做一个条件GET    if (cacheResponse != null) {      if (validate(cacheResponse, networkResponse)) { //比较确定缓存response可用        Response response = cacheResponse.newBuilder()            .headers(combine(cacheResponse.headers(), networkResponse.headers()))            .cacheResponse(stripBody(cacheResponse))            .networkResponse(stripBody(networkResponse))            .build();        networkResponse.body().close();        // Update the cache after combining headers but before stripping the        // Content-Encoding header (as performed by initContentStream()).          //更新缓存，在剥离content-Encoding之前        cache.trackConditionalCacheHit();        cache.update(cacheResponse, response);        return response;      } else {        closeQuietly(cacheResponse.body());      }    }    Response response = networkResponse.newBuilder()        .cacheResponse(stripBody(cacheResponse))        .networkResponse(stripBody(networkResponse))        .build();    if (HttpHeaders.hasBody(response)) {    // =========(5)      CacheRequest cacheRequest = maybeCache(response, networkResponse.request(), cache);      response = cacheWritingResponse(cacheRequest, response);    }    return response;  }

1. 首先，根据request来判断cache中是否有缓存的response，如果有，得到这个response，然后进行判断当前response是否有效，没有将cacheCandate赋值为空。
2. 根据request判断缓存的策略，是否要使用了网络，缓存 或两者都使用
3. 调用下一个拦截器，决定从网络上来得到response
4. 如果本地已经存在cacheResponse，那么让它和网络得到的networkResponse做比较，决定是否来更新缓存的cacheResponse

5. 缓存未经缓存过的response

   ConnectInterceptor:建立连接

   @Override public Response intercept(Chain chain) throws IOException {    RealInterceptorChain realChain = (RealInterceptorChain) chain;    Request request = realChain.request();    StreamAllocation streamAllocation = realChain.streamAllocation();    // We need the network to satisfy this request. Possibly for validating a conditional GET.    boolean doExtensiveHealthChecks = !request.method().equals("GET");    HttpCodec httpCodec = streamAllocation.newStream(client, doExtensiveHealthChecks);    RealConnection connection = streamAllocation.connection();    return realChain.proceed(request, streamAllocation, httpCodec, connection);}

实际上建立连接就是创建了一个HttpCodec对象，它将在后面的步骤中被使用，那它又是何方神圣呢？它是对 HTTP 协议操作的抽象，有两个实现：Http1Codec和Http2Codec，顾名思义，它们分别对应 HTTP/1.1 和 HTTP/2 版本的实现。

在Http1Codec中，它利用 Okio 对Socket的读写操作进行封装，Okio 以后有机会再进行分析，现在让我们对它们保持一个简单地认识：它对java.io和java.nio进行了封装，让我们更便捷高效的进行 IO 操作。

而创建HttpCodec对象的过程涉及到StreamAllocation、RealConnection，代码较长，这里就不展开，这个过程概括来说，就是找到一个可用的RealConnection，再利用RealConnection的输入输出（BufferedSource和BufferedSink）创建HttpCodec对象，供后续步骤使用。

NetworkInterceptors

配置OkHttpClient时设置的 NetworkInterceptors。

CallServerInterceptor：发送和接收数据

 @Override public Response intercept(Chain chain) throws IOException {    HttpCodec httpCodec = ((RealInterceptorChain) chain).httpStream();    StreamAllocation streamAllocation = ((RealInterceptorChain) chain).streamAllocation();    Request request = chain.request();    long sentRequestMillis = System.currentTimeMillis();    httpCodec.writeRequestHeaders(request);    if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {   //===(1)      Sink requestBodyOut = httpCodec.createRequestBody(request, request.body().contentLength());      BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);      request.body().writeTo(bufferedRequestBody);      bufferedRequestBody.close();    }    httpCodec.finishRequest();    Response response = httpCodec.readResponseHeaders()     //====(2)        .request(request)        .handshake(streamAllocation.connection().handshake())        .sentRequestAtMillis(sentRequestMillis)        .receivedResponseAtMillis(System.currentTimeMillis())        .build();    if (!forWebSocket || response.code() != 101) {      response = response.newBuilder()          .body(httpCodec.openResponseBody(response))          .build();    }    if ("close".equalsIgnoreCase(response.request().header("Connection"))        || "close".equalsIgnoreCase(response.header("Connection"))) {      streamAllocation.noNewStreams();    }    int code = response.code();    if ((code == 204 || code == 205) && response.body().contentLength() > 0) {      throw new ProtocolException(          "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());    }    return response;  }

1. 检查请求方法，用Httpcodec处理request
2. 进行网络请求得到response
3. 返回response

总结

前面说了拦截器用了责任链设计模式,它将请求一层一层向下传，知道有一层能够得到Resposne就停止向下传递，然后将response向上面的拦截器传递，然后各个拦截器会对respone进行一些处理，最后会传到RealCall类中通过execute来得到esponse。

异步请求的流程：

异步get请求示例如下：

private final OkHttpClient client = new OkHttpClient();  public void run() throws Exception {    Request request = new Request.Builder()        .url("http://publicobject.com/helloworld.txt")        .build();    client.newCall(request).enqueue(new Callback() {      @Override       public void onFailure(Call call, IOException e) {        e.printStackTrace();      }      @Override       public void onResponse(Call call, Response response) throws IOException {        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);        Headers responseHeaders = response.headers();        for (int i = 0, size = responseHeaders.size(); i < size; i++) {          System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));        }        System.out.println(response.body().string());      }    });  }

由代码中client.newCall(request).enqueue(Callback)，开始我们知道client.newCall(request)方法返回的是RealCall对象，接下来继续向下看enqueue()方法:

   //异步任务使用    @Override     public void enqueue(Callback responseCallback) {        synchronized (this) {            if (executed) throw new IllegalStateException("Already Executed");            executed = true;        }        client.dispatcher().enqueue(new AsyncCall(responseCallback));    }

调用了上面我们没有详细说的Dispatcher类中的enqueue(Call )方法.接着继续看：

synchronized void enqueue(AsyncCall call) {        if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {            runningAsyncCalls.add(call);            executorService().execute(call);        } else {            readyAsyncCalls.add(call);        }    }

如果中的runningAsynCalls不满，且call占用的host小于最大数量，则将call加入到runningAsyncCalls中执行，同时利用线程池执行call；否者将call加入到readyAsyncCalls中。runningAsyncCalls和readyAsyncCalls是什么呢？看下面：

/** Ready async calls in the order they'll be run. */private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>(); //正在准备中的异步请求队列/** Running asynchronous calls. Includes canceled calls that haven't finished yet. */private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>(); //运行中的异步请求/** Running synchronous calls. Includes canceled calls that haven't finished yet. */private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>(); //同步请求

call加入到线程池中执行了。现在再看AsynCall的代码，它是RealCall中的内部类:

//异步请求    final class AsyncCall extends NamedRunnable {        private final Callback responseCallback;        private AsyncCall(Callback responseCallback) {            super("OkHttp %s", redactedUrl());            this.responseCallback = responseCallback;        }        String host() {            return originalRequest.url().host();        }        Request request() {            return originalRequest;        }        RealCall get() {            return RealCall.this;        }        @Override protected void execute() {            boolean signalledCallback = false;            try {                Response response = getResponseWithInterceptorChain();                if (retryAndFollowUpInterceptor.isCanceled()) {                    signalledCallback = true;                    responseCallback.onFailure(RealCall.this, new IOException("Canceled"));                } else {                    signalledCallback = true;                    responseCallback.onResponse(RealCall.this, response);                }            } catch (IOException e) {                if (signalledCallback) {                    // Do not signal the callback twice!                    Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);                } else {                    responseCallback.onFailure(RealCall.this, e);                }            } finally {                client.dispatcher().finished(this);            }        }    }

AysncCall中的execute()中的方法，同样是通过Response response = getResponseWithInterceptorChain();来获得response，这样异步任务也同样通过了interceptor，剩下的流程就和上面一样了。

摘自http://www.jianshu.com/p/27c1554b7fee

连接池的复用和缓存
http://www.jianshu.com/p/aad5aacd79bf