Okhttp3学习笔记

OkHttp的基本使用

String url = "http://wwww.baidu.com";
//(1)创建一个OKhttpClient
OkHttpClient okHttpClient = new OkHttpClient();

//(2)创建一个Request
final Request request = new Request.Builder()
        .url(url)
        .build();
//(3)okHttpClient 调用newCall()方法 创建一个Call对象
Call call = okHttpClient.newCall(request);
//(4)call调用enqueue()方法,这次请求Call添加到任务队列，并通过CallBack接收返回结果。
call.enqueue(new Callback() {
    @Override
    public void onFailure(Call call, IOException e) {
        Log.d(TAG, "onFailure: ");
    }

    @Override
    public void onResponse(Call call, Response response) throws IOException {
        Log.d(TAG, "onResponse: " + response.body().string());
    }
});

• 在OkHttp3中，每一个请求任务都封装为一个Call，其实现为RealCall。
• 而所有的策略几乎都可以通过OkHttpClient传入
• 所有全局策略与数据，除了存储在允许上层访问的OkHttpClient实例以外，还有一部分是存储在只允许包可见的Internal.instance中（如连接池、路由黑名单等)
• OkHttp中用户可传入的interceptor分为两类，一类是全局interceptor，该类interceptor在请求开始之前最早被调用，另外一类为非网页请求的networkInterceptor，这类interceptor只有在非网页请求中会被调用，并且是在组装完成请求之后，真正发起请求之前被调用(这块具体可以参看RealCall#getResponseWithInterceptorChain()方法)
• 整个请求过程通过RealInterceptorChain#proceed来连接，在每个interceptor中调用下一个interceptor来完成整个请求流程，并且在回到当前interceptor后完成响应处理
• 在异步请求中，我们通过Callback来获得简单清晰的请求回调(onFailure、onResponse)
• 在OkHttpClient中，我们可以传入EventListener的工厂方法，为每一个请求创建一个EventListener，来接收非常细的事件回调

一、OKHttp3 原理介绍

1、okHttp中大量使用了Builder设置模式

如

OkHttpClient.Builder
Request.Builder

Builder机制的优势是 可以规避大量参数构造方法不灵活的缺点，和set方法不能保证对象的合法性问题。并且Builder采用链式调用，使用方便灵活。

2、Request 类

Request类其实是一个数据承载类，主要承载网络请求的参数信息，代表着一个网络请求。如method(get 或post),HttpUrl(scheme、host、port),headers 和RequestBody

public final class Request {
  final HttpUrl url;
  final String method;
  final Headers headers;
  final @Nullable RequestBody body;
  final Object tag;

  private volatile CacheControl cacheControl; // Lazily initialized.

  Request(Builder builder) {
    this.url = builder.url;
    this.method = builder.method;
    this.headers = builder.headers.build();
    this.body = builder.body;
    this.tag = builder.tag != null ? builder.tag : this;
  }
}

3、OkHttpClient 类,也是一个载体类，一个工具箱。它承载http请求相关的策略参数、拦截器、调度分发器、超时时间、连接池等。

public class OkHttpClient implements Cloneable, Call.Factory, WebSocket.Factory {
 final Dispatcher dispatcher;
  final @Nullable Proxy proxy;
  final List<Protocol> protocols;
  final List<ConnectionSpec> connectionSpecs;
  final List<Interceptor> interceptors;
  final List<Interceptor> networkInterceptors;
  final EventListener.Factory eventListenerFactory;
  final ProxySelector proxySelector;
  final CookieJar cookieJar;
  final @Nullable Cache cache;
  final @Nullable InternalCache internalCache;
  final SocketFactory socketFactory;
  final @Nullable SSLSocketFactory sslSocketFactory;
  final @Nullable CertificateChainCleaner certificateChainCleaner;
  final HostnameVerifier hostnameVerifier;
  final CertificatePinner certificatePinner;
  final Authenticator proxyAuthenticator;
  final Authenticator authenticator;
  final ConnectionPool connectionPool;
  final Dns dns;
  final boolean followSslRedirects;
  final boolean followRedirects;
  final boolean retryOnConnectionFailure;
  final int connectTimeout;
  final int readTimeout;
  final int writeTimeout;
  final int pingInterval;

}

OkHttpClient 继承自Call.Factory，实现了newCall()方法

interface Factory {
    Call newCall(Request request);
  }
  
   @Override public Call newCall(Request request) {
    return RealCall.newRealCall(this, request, false /* for web socket */);
  }

RealCall类中newRealCall（）

   static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
    // Safely publish the Call instance to the EventListener.
    RealCall call = new RealCall(client, originalRequest, forWebSocket);
    call.eventListener = client.eventListenerFactory().create(call);
    return call;
  }

okHttpClient的newCall方法内部调用的是RealCall的newRealCall()方法，传入okHttpClient对象（一个公共工具箱）和Request对象(什么网络请求)，返回一个RealCalL对象。

4、RealCall 类

RealCall集成自Call接口

public interface Call extends Cloneable {

  //返回request请求
  Request request();

  //同步执行网络请求
  Response execute() throws IOException;

  //异步执行网路请求
  void enqueue(Callback responseCallback);

 //取消执行
  void cancel();

  boolean isExecuted();

  boolean isCanceled();

  Call clone();

  interface Factory {
    Call newCall(Request request);
  }

RealCall类是网络请求的具体实施类。持有OkhttpClient(大工具箱)，和Request对象(网络请求)

（1）execute() 同步执行网路请求

  @Override public Response execute() throws IOException {
    synchronized (this) {
    
      //保证仅执行一次
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    eventListener.callStart(this);
    try {
      //将该Call 添加到分发器中的同步队列中.
      client.dispatcher().executed(this);
      //网络请求真正执行的地方
      Response result = getResponseWithInterceptorChain();
      if (result == null) throw new IOException("Canceled");
      return result;
    } catch (IOException e) {
      eventListener.callFailed(this, e);
      throw e;
    } finally {
      // realCall执行完成，尝试将待执异步任务添加到 异步执行队列
      client.dispatcher().finished(this);
    }
  }

（2）enqueue() 异步执行网络请求

realCall.enqueue() 的具体调用过程，如下图
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 @Override public void enqueue(Callback responseCallback) {
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    eventListener.callStart(this);
    //将RealCall 封装成一个AsyncCall同时添加到异步执行队列中。
    client.dispatcher().enqueue(new AsyncCall(responseCallback));
  }

AsyncCall 继承自NamedRunnable类，同时是RealCall的内部类，真正的执行过程位于execute中。

• NamedRunnable 为Runnable 添加了一个名称属性,成为可命名的Runnable,并将run()方法任务 代理到 虚方法execute()方法中

public abstract class NamedRunnable implements Runnable {
  protected final String name;

  public NamedRunnable(String format, Object... args) {
    this.name = Util.format(format, args);
  }

  @Override public final void run() {
    String oldName = Thread.currentThread().getName();
    Thread.currentThread().setName(name);
    try {
      execute();
    } finally {
      Thread.currentThread().setName(oldName);
    }
  }

  protected abstract void execute();
}

• AsyncCall继承自NamedRunnable,execuate()方法中，通过责任链getResponseWithInterceptorChain()来完成请求操作

final class AsyncCall extends NamedRunnable {
    private final Callback responseCallback;

    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 {
      
        //请求执行的代码
        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 {
          eventListener.callFailed(RealCall.this, e);
          responseCallback.onFailure(RealCall.this, e);
        }
      } finally {
        client.dispatcher().finished(this);
      }
    }
  }

（3）网络请求真正被执行的地方

getResponseWithInterceptorChain() 方法
可以看到该方法中天剑了一个Interceptor.Chain 拦截器链，同时添加了很多连接器。

真正的网络请求在CallServerInterceptor 拦截器中处理

  Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());
    interceptors.add(retryAndFollowUpInterceptor);
    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, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

    return chain.proceed(originalRequest);
  }
}

5、 Dispatcher类 负责任务的分发

• Dispatcher 内部持有一个线程池
• 持有两个异步队列readyAsyncCalls(待执行异步任务队列)和runningAsyncCalls（正在执行的异步任务队列）
• 持有一个同步队列：runningSyncCalls（正在执行的同步任务）

public final class Dispatcher {
  private int maxRequests = 64;
  private int maxRequestsPerHost = 5;
  private @Nullable Runnable idleCallback;

  /** Executes calls. Created lazily. */
  private @Nullable ExecutorService executorService;

  /** Ready async calls in the order they'll be run. */
  private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();

  /** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
  private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();

  /** Running synchronous calls. Includes canceled calls that haven't finished yet. */
  private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();

  public Dispatcher(ExecutorService executorService) {
    this.executorService = executorService;
  }

  public Dispatcher() {
  }

  public synchronized ExecutorService executorService() {
    if (executorService == null) {
      executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
          new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false));
    }
    return executorService;
  }
}

队列管理

异步任务入列时，首先会判断 正在执行的异步任务个数是否小于可同时执行的任务个数，若是，则将call添加到runningAsyncCalls队列，同时在线程池中执行该Call任务

若否，说明任务忙，将Call添加到等待执行队列readyAsyncCalls

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

当某个任务执行完成后，都会调用promoteCalls（）,尝试将等待队列中的任务，切换到正在执行队列，并在线程池中执行call任务。

  private void promoteCalls() {
    if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
    if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.

    for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
      AsyncCall call = i.next();

      if (runningCallsForHost(call) < maxRequestsPerHost) {
        i.remove();
        runningAsyncCalls.add(call);
        executorService().execute(call);
      }

      if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity.
    }
  }

/** Used by {@code Call#execute} to signal completion. */
  void finished(RealCall call) {
    finished(runningSyncCalls, call, false);
  }

  private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
    int runningCallsCount;
    Runnable idleCallback;
    synchronized (this) {
      if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
      if (promoteCalls) promoteCalls();
      runningCallsCount = runningCallsCount();
      idleCallback = this.idleCallback;
    }

    if (runningCallsCount == 0 && idleCallback != null) {
      idleCallback.run();
    }
  }

二、OKHttp 中拦截器链是其整个框架的精髓

image

用户可传入的 interceptor 分为两类：

• ①一类是全局的 interceptor，该类 interceptor 在整个拦截器链中最早被调用，通过 OkHttpClient.Builder#addInterceptor(Interceptor) 传入；
• ②另外一类是非网页请求的 interceptor ，这类拦截器只会在非网页请求中被调用，并且是在组装完请求之后，真正发起网络请求前被调用，所有的 interceptor 被保存在 List<Interceptor> interceptors 集合中，按照添加顺序来逐个调用。具体可参考 RealCall#getResponseWithInterceptorChain() 方法。通过 OkHttpClient.Builder#addNetworkInterceptor(Interceptor) 传入；

image

1、RetryAndFollowUpInterceptor 负责错误重试

如下面所示,外层是一个while(true)循环,执行完请求之后,由followUpRequest(response, route)判定是应该重试,直到followUp == null 退出循环。

class RetryAndFollowUpInterceptor(private val client: OkHttpClient) : Interceptor {

  @Throws(IOException::class)
  override fun intercept(chain: Interceptor.Chain): Response {
    var request = chain.request()
    val realChain = chain as RealInterceptorChain
    var followUpCount = 0
    var priorResponse: Response? = null

    //(1) while 死循环
    while (true) {
   

      var response: Response
      var success = false
      try {
        // 执行请求
        response = realChain.proceed(request, transmitter, null)
        success = true
      } catch (e: RouteException) {
        // The attempt to connect via a route failed. The request will not have been sent.
        if (!recover(e.lastConnectException, transmitter, false, request)) {
          throw e.firstConnectException
        }
        continue
      } catch (e: IOException) {
        // An attempt to communicate with a server failed. The request may have been sent.
        val requestSendStarted = e !is ConnectionShutdownException
        if (!recover(e, transmitter, requestSendStarted, request)) throw e
        continue
      } finally {
        // The network call threw an exception. Release any resources.
        if (!success) {
          transmitter.exchangeDoneDueToException()
        }
      }

      val exchange = response.exchange
      val route = exchange?.connection()?.route()
      //(3) 错误处理,followUp ！= null 则进行重试
      val followUp = followUpRequest(response, route)

      if (followUp == null) {
        if (exchange != null && exchange.isDuplex) {
          transmitter.timeoutEarlyExit()
        }
        return response
      }
    }
}

2、BridgeInterceptor 主要负责添加某些请求头Headers

class BridgeInterceptor(private val cookieJar: CookieJar) : Interceptor {

  @Throws(IOException::class)
  override fun intercept(chain: Interceptor.Chain): Response {
    val userRequest = chain.request()
    val requestBuilder = userRequest.newBuilder()

    val body = userRequest.body
    if (body != null) {
      val contentType = body.contentType()
      if (contentType != null) {
        requestBuilder.header("Content-Type", contentType.toString())
      }

      val contentLength = body.contentLength()
      if (contentLength != -1L) {
        requestBuilder.header("Content-Length", contentLength.toString())
        requestBuilder.removeHeader("Transfer-Encoding")
      } else {
        requestBuilder.header("Transfer-Encoding", "chunked")
        requestBuilder.removeHeader("Content-Length")
      }
    }

    if (userRequest.header("Host") == null) {
      requestBuilder.header("Host", userRequest.url.toHostHeader())
    }

    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.
    var transparentGzip = false
    if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
      transparentGzip = true
      requestBuilder.header("Accept-Encoding", "gzip")
    }

    val cookies = cookieJar.loadForRequest(userRequest.url)
    if (cookies.isNotEmpty()) {
      requestBuilder.header("Cookie", cookieHeader(cookies))
    }

    if (userRequest.header("User-Agent") == null) {
      requestBuilder.header("User-Agent", userAgent)
    }

    val networkResponse = chain.proceed(requestBuilder.build())

    cookieJar.receiveHeaders(userRequest.url, networkResponse.headers)

    val responseBuilder = networkResponse.newBuilder()
        .request(userRequest)

    ...
    return responseBuilder.build()
  }

3、CacheInterceptor 主要是处理缓存的策略

class CacheInterceptor(internal val cache: Cache?) : Interceptor {

  @Throws(IOException::class)
  override fun intercept(chain: Interceptor.Chain): Response {
    val cacheCandidate = cache?.get(chain.request())

    val now = System.currentTimeMillis()

    val strategy = CacheStrategy.Factory(now, chain.request(), cacheCandidate).compute()
    val networkRequest = strategy.networkRequest
    val cacheResponse = strategy.cacheResponse

    cache?.trackResponse(strategy)

    if (cacheCandidate != null && cacheResponse == null) {
      // The cache candidate wasn't applicable. Close it.
      cacheCandidate.body?.closeQuietly()
    }

    //(1)禁止使用网络请求，切无有效的本地缓存，则直接返回失败
    // If we're forbidden from using the network and the cache is insufficient, fail.
    if (networkRequest == null && cacheResponse == null) {
      return Response.Builder()
          .request(chain.request())
          .protocol(Protocol.HTTP_1_1)
          .code(HTTP_GATEWAY_TIMEOUT)
          .message("Unsatisfiable Request (only-if-cached)")
          .body(EMPTY_RESPONSE)
          .sentRequestAtMillis(-1L)
          .receivedResponseAtMillis(System.currentTimeMillis())
          .build()
    }

    //(2) 需要要请求网络,则直接返回缓存数据
    // If we don't need the network, we're done.
    if (networkRequest == null) {
      return cacheResponse!!.newBuilder()
          .cacheResponse(stripBody(cacheResponse))
          .build()
    }


    var networkResponse: Response? = null
    try {
     //(3) 重新从网络获取
      networkResponse = chain.proceed(networkRequest)
    } finally {
      // If we're crashing on I/O or otherwise, don't leak the cache body.
      if (networkResponse == null && cacheCandidate != null) {
        cacheCandidate.body?.closeQuietly()
      }
    }

4、ConnectInterceptor 负责建立一个实际的网络链接

object ConnectInterceptor : Interceptor {

  @Throws(IOException::class)
  override fun intercept(chain: Interceptor.Chain): Response {
    val realChain = chain as RealInterceptorChain
    val request = realChain.request()
    val transmitter = realChain.transmitter()

    // We need the network to satisfy this request. Possibly for validating a conditional GET.
    val doExtensiveHealthChecks = request.method != "GET"
    //(1)生成一个新的Exchange对象。Exchange代表一个网络链接
    val exchange = transmitter.newExchange(chain, doExtensiveHealthChecks)

    return realChain.proceed(request, transmitter, exchange)
  }
}

5、CallServerInterceptor 负责访问服务器

class CallServerInterceptor(private val forWebSocket: Boolean) : Interceptor {

  @Throws(IOException::class)
  override fun intercept(chain: Interceptor.Chain): Response {
    val realChain = chain as RealInterceptorChain
    val exchange = realChain.exchange()
    val request = realChain.request()
    val requestBody = request.body
    val sentRequestMillis = System.currentTimeMillis()

    exchange.writeRequestHeaders(request)

    var responseHeadersStarted = false
    var responseBuilder: Response.Builder? = null
    if (HttpMethod.permitsRequestBody(request.method) && requestBody != null) {
      // If there's a "Expect: 100-continue" header on the request, wait for a "HTTP/1.1 100
      // Continue" response before transmitting the request body. If we don't get that, return
      // what we did get (such as a 4xx response) without ever transmitting the request body.
 
      if (responseBuilder == null) {
        if (requestBody.isDuplex()) {
          // Prepare a duplex body so that the application can send a request body later.
          exchange.flushRequest()
          val bufferedRequestBody = exchange.createRequestBody(request, true).buffer()
          requestBody.writeTo(bufferedRequestBody)
        } else {
          // Write the request body if the "Expect: 100-continue" expectation was met.
          val bufferedRequestBody = exchange.createRequestBody(request, false).buffer()
          requestBody.writeTo(bufferedRequestBody)
          bufferedRequestBody.close()
        }
      } 
    } 

    if (requestBody == null || !requestBody.isDuplex()) {
      exchange.finishRequest()
    }
    if (!responseHeadersStarted) {
      exchange.responseHeadersStart()
    }
    if (responseBuilder == null) {
      responseBuilder = exchange.readResponseHeaders(false)!!
    }
    var response = responseBuilder
        .request(request)
        .handshake(exchange.connection()!!.handshake())
        .sentRequestAtMillis(sentRequestMillis)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build()
    var code = response.code
    if (code == 100) {
      // server sent a 100-continue even though we did not request one.
      // try again to read the actual response
      response = exchange.readResponseHeaders(false)!!
          .request(request)
          .handshake(exchange.connection()!!.handshake())
          .sentRequestAtMillis(sentRequestMillis)
          .receivedResponseAtMillis(System.currentTimeMillis())
          .build()
      code = response.code
    }

    exchange.responseHeadersEnd(response)

    response = if (forWebSocket && code == 101) {
      // Connection is upgrading, but we need to ensure interceptors see a non-null response body.
      response.newBuilder()
          .body(EMPTY_RESPONSE)
          .build()
    } else {
      response.newBuilder()
          .body(exchange.openResponseBody(response))
          .build()
    }
    i
    return response
  }
}

三、如何实现一个拦截器

1、定义拦截器接口Interceptor 和连接器链Chain

• Interceptor 最主要方法是intercept(),参数为拦截链，返回值为Respone结果。
• Interceptor.Chain 拦截器链最主要的方法为proceed（）参数为Request

public interface Interceptor {
  Response intercept(Chain chain) throws IOException;

  interface Chain {
    Request request();

    Response proceed(Request request) throws IOException;

    @Nullable Connection connection();

    Call call();
  }
}

2、实现Interceptor 定义具体的拦截器

实现intercept()方法

• 请求预处理过程:取出原始request ，对原始request请求做相应的处理，生产一个新的Request
• 调用chain.proceed，将新request传递到下一个拦截器进行处理
• 下一个拦截器返回处理结果后，可以对结果进行二次处理，返回给上一个拦截器。

public final class BridgeInterceptor implements Interceptor {
  private final CookieJar cookieJar;

  public BridgeInterceptor(CookieJar cookieJar) {
    this.cookieJar = cookieJar;
  }

  @Override public Response intercept(Chain chain) throws IOException {
  
    //（1）取出原始request ，对原始request请求做相应的处理，生产一个新的Request
    Request userRequest = chain.request();
    Request.Builder requestBuilder = userRequest.newBuilder();


    if (userRequest.header("Host") == null) {
      requestBuilder.header("Host", hostHeader(userRequest.url(), false));
    }

    //(2)将新request传递到下一个拦截器进行处理
    Response networkResponse = chain.proceed(requestBuilder.build());


    //(3)获取到下一个拦截器处理的结果，可以对结果进行一些后处理。然后返回给上一个拦截器。
    HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());

    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);
      String contentType = networkResponse.header("Content-Type");
      responseBuilder.body(new RealResponseBody(contentType, -1L, Okio.buffer(responseBody)));
    }

    return responseBuilder.build();
  }

3、实现具体的Interceptor.Chain

public final class RealInterceptorChain implements Interceptor.Chain{
    
    //interceptors 数组
    private final List<Interceptor> interceptors;
    //index指示当前 需要哪个Interceptor 处理Request
    private final int index;
    //记录当前的request请求
    private final Request request;
        
        
 @Override public Response proceed(Request request) throws IOException {
    return proceed(request, streamAllocation, httpCodec, connection);
  }


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

 

    //(1)Clone出一个新的RealInterceptorChain,更新原来的requst,index+1,将当前interceptor的下一个拦截器为当前的interceptor。
    RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
        connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
        writeTimeout);
    
    //(2)执行当前interceptor的intercept()方法,将Clone出来的  RealInterceptorChain 作为参数传递给拦截器。
    Interceptor interceptor = interceptors.get(index);
    Response response = interceptor.intercept(next);


    //返回response
    return response;
  }
}

到此 一个建议的拦截器链 完成。拦截器有很多应用，如Okhttp库，组件化方法CC库都用拦截器实现了其核心接口。

四、参考文章

https://www.jianshu.com/p/9deec36f2759