OkHttp_3.12.0源碼分析

OkHttp_3.12.0源碼分析

基於OkHttp:3.12.0:github.com/square/okht…

RTFSC

Read The Fucking Source Code

流程分析

1. 用戶層面調用形式：

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

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2. OkHttpClient#newCall(new Request())：OkHttpClient根據client、request建立RealCall，RealCall裏面包含全部請求的各類配置信息:攔截器、請求鏈接、調度器Dispatcher、ConnectionPool等

//OkHttpClient
@Override public Call newCall(Request request) {
    return RealCall.newRealCall(this, request, false /* for web socket */);
  }
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3. RealCall#enqueue(new Callback(){}):
   1. 經過RealCall中的client間接獲取Dispatcher--維護一個線程池、readyAsyncCalls、runningAsyncCalls、runningSyncCalls三個請求隊列。
   2. Dispatcher的enqueue會把當前的responseCallback包裝成AsyncCall的形式放入readyAsyncCalls隊列中，注意AsyncCall實現了Runnable接口。

//RealCall
@Override public void enqueue(Callback responseCallback) {
     //其它信息...    
     client.dispatcher().enqueue(new AsyncCall(responseCallback));
  }
  
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// Dispatcher    
 void enqueue(AsyncCall call) {
    synchronized (this) {
         readyAsyncCalls.add(call);
        }
        promoteAndExecute();
    } 
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4. Dispatcher#promoteAndExecute：這一步會遍歷readyAsyncCalls把準備隊列中的AsyncCall放到runningAsyncCalls運行隊列中；同時放到立馬執行的一個列表中：executableCalls。這裏一些額外的判斷是：，請求是否超過了最大請求數maxRequests，同一個host是否大於maxRequestsPerHostmaxRequests。

//Dispatcher
    private boolean promoteAndExecute() {
        //...
        List<AsyncCall> executableCalls = new ArrayList<>();
        //僞代碼...
        if(知足必定條件){executableCalls.addAll(readyAsyncCalls)}
    
        for (int i = 0, size = executableCalls.size(); i < size; i++) {
          AsyncCall asyncCall = executableCalls.get(i);
          asyncCall.executeOn(executorService());
        }
    
        return isRunning;
      }
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5. AsyncCall#executeOn(executorService()):

   1. AsyncCall#executeOn(ExecutorService):經過線程池執行當前對象，會調用上層NamedRunnable的run()方法。重點：這裏完成線程切換邏輯，由於下面就要開始去執行耗時操做。
   2. NamedRunnable#run方法會調用execute(),具體邏輯在子類AsyncCall實現。
   3. AsyncCall#execute()是真正獲取Response值、把值回調給responseCallback的步驟。

//AsyncCall 
   void executeOn(ExecutorService executorService) {
       //...
       executorService.execute(this);//這裏會調用父類的run方法
       //...
   }
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//NamedRunnable, AsyncCall的父類  
    public abstract class NamedRunnable implements Runnable {
      //...    
      @Override public final void run() {
        //...
        execute();
      }
      //子類AsyncCall作對應實現
      protected abstract void execute();
    }        
        
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#AsyncCall
   @Override protected void execute() {
       boolean signalledCallback = false;
       timeout.enter();
       try {
       //關鍵，去獲取response對象，真正的耗時也就在這
       Response response = getResponseWithInterceptorChain();
       if (retryAndFollowUpInterceptor.isCanceled()) {
           signalledCallback = true;
           //失敗，請求被取消
            responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
       } else {
           signalledCallback = true;
           //成功請求，拿去結果回調
           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
             responseCallback.onFailure(RealCall.this, e);
       }
         } finally {
           //完整結束當前請求，作一些收尾操做
           client.dispatcher().finished(this);
         }
       }
     }
     
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6. RealCall#getResponseWithInterceptorChain:
   1. RealCall#getResponseWithInterceptorChain會把用戶自定義的攔截器、系統級別的攔截器放到list中組裝好，給一個new RealInterceptorChain。這裏須要注意攔截器加入的順序，用戶攔截器優先級最高->系統一些中間攔截->最後網絡請求。
   2. RealInterceptorChain#proceed在這裏會構造一個新的RealInterceptorChain:next，注意新的RealInterceptorChain中index+1;另外根據當前的index取得當前攔截器，執行攔截器中惟一的方法intercept(next)，具體執行的哪個呢，就看上層實現的是哪個具體實現。
   3. 咱們隨便看一個實現，假如BridgeInterceptor:會在BridgeInterceptor中執行BridgeInterceptor相關的實現，最關鍵的會執行chain.proceed(requestBuilder.build()),注意Chain是上一個建立的RealInterceptorChain，因此又跑到了第二步，同時index這個時候已經+1，如此完成遞歸操做！
   4. 通過二、3兩步，經過迭代操做，完整全部攔截器的執行。至於說網絡請求、緩存、重試、日誌等等核心包括外圍功能，所有經過攔截器實現，而且責任分明，高度解耦合，實現方式：責任鏈模式。

#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);
  }
  
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#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 {
    //...
    
    //注意這裏又構造了一個RealInterceptorChain，重點index+1
    RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
        connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
        writeTimeout);
        
    //取當前index對應的攔截器
    Interceptor interceptor = interceptors.get(index);
    //執行取到的攔截器
    Response response = interceptor.intercept(next);
    
    //...
    return response;
  }

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# BridgeInterceptor
@Override public Response intercept(Chain chain) throws IOException {
    //根據上游chain繼續處理當前攔截器。注意：chain的源頭：RealInterceptorChain#proceed中建立的next,一個新的RealInterceptorChain
    Request userRequest = chain.request();
    Request.Builder requestBuilder = userRequest.newBuilder();

    //各類邏輯，跳過只看核心...
    
    //核心，這裏又回到了RealInterceptorChain#proceed
    Response networkResponse = chain.proceed(requestBuilder.build());

    //後續邏輯...

    return responseBuilder.build();
  }

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