OkHttp_3.12.0源碼分析

基于OkHttp:3.12.0:https://github.com/square/okhttp/tree/okhttp_3.12.x

RTFSC

Read The Fucking Source Code

流程分析

1. 用戶層面調(diào)用形式：

OkHttpClient#newCall(new Request())#enquenue(new Callback(){})

2. OkHttpClient#newCall(new Request())：OkHttpClient根據(jù)client、request創(chuàng)建RealCall，RealCall里面包含所有請(qǐng)求的各種配置信息:攔截器、請(qǐng)求連接、調(diào)度器Dispatcher、ConnectionPool等

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

3. RealCall#enqueue(new Callback(){}):
   1. 通過(guò)RealCall中的client間接獲取Dispatcher--維護(hù)一個(gè)線程池、readyAsyncCalls、runningAsyncCalls、runningSyncCalls三個(gè)請(qǐng)求隊(duì)列。
   2. Dispatcher的enqueue會(huì)把當(dāng)前的responseCallback包裝成AsyncCall的形式放入readyAsyncCalls隊(duì)列中，注意AsyncCall實(shí)現(xiàn)了Runnable接口。

//RealCall
@Override public void enqueue(Callback responseCallback) {
     //其它信息...    
     client.dispatcher().enqueue(new AsyncCall(responseCallback));
  }
  

// Dispatcher    
 void enqueue(AsyncCall call) {
    synchronized (this) {
         readyAsyncCalls.add(call);
        }
        promoteAndExecute();
    } 

4. Dispatcher#promoteAndExecute：這一步會(huì)遍歷readyAsyncCalls把準(zhǔn)備隊(duì)列中的AsyncCall放到runningAsyncCalls運(yùn)行隊(duì)列中；同時(shí)放到立馬執(zhí)行的一個(gè)列表中：executableCalls。這里一些額外的判斷是：，請(qǐng)求是否超過(guò)了最大請(qǐng)求數(shù)maxRequests，同一個(gè)host是否大于maxRequestsPerHostmaxRequests。

    //Dispatcher
    private boolean promoteAndExecute() {
        //...
        List<AsyncCall> executableCalls = new ArrayList<>();
        //偽代碼...
        if(滿足一定條件){executableCalls.addAll(readyAsyncCalls)}
    
        for (int i = 0, size = executableCalls.size(); i < size; i++) {
          AsyncCall asyncCall = executableCalls.get(i);
          asyncCall.executeOn(executorService());
        }
    
        return isRunning;
      }

5. AsyncCall#executeOn(executorService()):

   1. AsyncCall#executeOn(ExecutorService):通過(guò)線程池執(zhí)行當(dāng)前對(duì)象，會(huì)調(diào)用上層NamedRunnable的run()方法。重點(diǎn)：這里完成線程切換邏輯，因?yàn)橄旅婢鸵_始去執(zhí)行耗時(shí)操作。
   2. NamedRunnable#run方法會(huì)調(diào)用execute(),具體邏輯在子類AsyncCall實(shí)現(xiàn)。
   3. AsyncCall#execute()是真正獲取Response值、把值回調(diào)給responseCallback的步驟。

   //AsyncCall 
   void executeOn(ExecutorService executorService) {
       //...
       executorService.execute(this);//這里會(huì)調(diào)用父類的run方法
       //...
   }

    //NamedRunnable, AsyncCall的父類  
    public abstract class NamedRunnable implements Runnable {
      //...    
      @Override public final void run() {
        //...
        execute();
      }
      //子類AsyncCall做對(duì)應(yīng)實(shí)現(xiàn)
      protected abstract void execute();
    }        
        

   #AsyncCall
   @Override protected void execute() {
       boolean signalledCallback = false;
       timeout.enter();
       try {
       //關(guān)鍵，去獲取response對(duì)象，真正的耗時(shí)也就在這
       Response response = getResponseWithInterceptorChain();
       if (retryAndFollowUpInterceptor.isCanceled()) {
           signalledCallback = true;
           //失敗，請(qǐng)求被取消
            responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
       } else {
           signalledCallback = true;
           //成功請(qǐng)求，拿去結(jié)果回調(diào)
           responseCallback.onResponse(RealCall.this, response);
           }
        } catch (IOException e) {
           e = timeoutExit(e);
           if (signalledCallback) {
             // Do not signal the callback twice!
             Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
           } else {
             eventListener.callFailed(RealCall.this, e);
             //失敗，回調(diào)
             responseCallback.onFailure(RealCall.this, e);
       }
         } finally {
           //完整結(jié)束當(dāng)前請(qǐng)求，做一些收尾操作
           client.dispatcher().finished(this);
         }
       }
     }
     

6. RealCall#getResponseWithInterceptorChain:
   1. RealCall#getResponseWithInterceptorChain會(huì)把用戶自定義的攔截器、系統(tǒng)級(jí)別的攔截器放到list中組裝好，給一個(gè)new RealInterceptorChain。這里需要注意攔截器加入的順序，用戶攔截器優(yōu)先級(jí)最高->系統(tǒng)一些中間攔截->最后網(wǎng)絡(luò)請(qǐng)求。
   2. RealInterceptorChain#proceed在這里會(huì)構(gòu)造一個(gè)新的RealInterceptorChain:next，注意新的RealInterceptorChain中index+1;另外根據(jù)當(dāng)前的index取得當(dāng)前攔截器，執(zhí)行攔截器中唯一的方法intercept(next)，具體執(zhí)行的哪一個(gè)呢，就看上層實(shí)現(xiàn)的是哪一個(gè)具體實(shí)現(xiàn)。
   3. 我們隨便看一個(gè)實(shí)現(xiàn)，假如BridgeInterceptor:會(huì)在BridgeInterceptor中執(zhí)行BridgeInterceptor相關(guān)的實(shí)現(xiàn)，最關(guān)鍵的會(huì)執(zhí)行chain.proceed(requestBuilder.build()),注意Chain是上一個(gè)創(chuàng)建的RealInterceptorChain，所以又跑到了第二步，同時(shí)index這個(gè)時(shí)候已經(jīng)+1，如此完成遞歸操作！
   4. 經(jīng)過(guò)2、3兩步，通過(guò)迭代操作，完整所有攔截器的執(zhí)行。至于說(shuō)網(wǎng)絡(luò)請(qǐng)求、緩存、重試、日志等等核心包括外圍功能，全部通過(guò)攔截器實(shí)現(xiàn)，并且責(zé)任分明，高度解耦合，實(shí)現(xiàn)方式：責(zé)任鏈模式。

#RealCall
Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    //用戶添加的自定義攔截器
    interceptors.addAll(client.interceptors());
    //重試
    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);
  }
  

#RealInterceptorChain
@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 {
    //...
    
    //注意這里又構(gòu)造了一個(gè)RealInterceptorChain，重點(diǎn)index+1
    RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
        connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
        writeTimeout);
        
    //取當(dāng)前index對(duì)應(yīng)的攔截器
    Interceptor interceptor = interceptors.get(index);
    //執(zhí)行取到的攔截器
    Response response = interceptor.intercept(next);
    
    //...
    return response;
  }

# BridgeInterceptor
@Override public Response intercept(Chain chain) throws IOException {
    //根據(jù)上游chain繼續(xù)處理當(dāng)前攔截器。注意：chain的源頭：RealInterceptorChain#proceed中創(chuàng)建的next,一個(gè)新的RealInterceptorChain
    Request userRequest = chain.request();
    Request.Builder requestBuilder = userRequest.newBuilder();

    //各種邏輯，跳過(guò)只看核心...
    
    //核心，這里又回到了RealInterceptorChain#proceed
    Response networkResponse = chain.proceed(requestBuilder.build());

    //后續(xù)邏輯...

    return responseBuilder.build();
  }