定義：Okhttp是對Socket的封裝。有三個(gè)主要的類喳挑，Request彬伦，Response，Call
默認(rèn)使用new OkHttpClient() 創(chuàng)建初client對象伊诵。
如果需要初始化網(wǎng)絡(luò)請求的參數(shù)单绑，如timeout,interceptor等，可以創(chuàng)建Builder曹宴，通過builder.build() 創(chuàng)建初client對象搂橙。

三個(gè)問題

1.請求發(fā)送到什么哪去了？框架里放到哪里了笛坦？
請求通過execute方法發(fā)送到框架中的兩個(gè)隊(duì)列中去了:運(yùn)行中的隊(duì)列区转；等待中的隊(duì)列，如果說運(yùn)行中的隊(duì)列總數(shù)小于64并且訪問同一目標(biāo)機(jī)器請求小于5版扩，就進(jìn)入運(yùn)行隊(duì)列废离，否則進(jìn)入等待隊(duì)列

2.請求被誰處理：請求提交到運(yùn)行中隊(duì)列后，交給線程池來處理礁芦，直接處理請求

3.請求是怎么被維護(hù)的：每次請求完成后蜻韭，client.dispath調(diào)用finished方法，對運(yùn)行中的隊(duì)列和等待中的隊(duì)列進(jìn)行數(shù)據(jù)處理柿扣，（在符合條件的情況下肖方，將等待中的加入到運(yùn)行中隊(duì)列中去）

流程

1.通過
生成一個(gè)OkHttpClient client = new OkHttpClient();

2.構(gòu)建一個(gè)Request requet = new Request.Builder()
.get().url("https:www.baidu.com").build();
3.通過client.newCall(request)得到Call,這個(gè)call是他的子類RealCall

4.通過call.execute(同步) 或call.enqueue(異步)啟動(dòng)

A：執(zhí)行Execute

@Override public Response execute() throws IOException {
  synchronized (this) {
    if (executed) throw new IllegalStateException("Already Execu
ted");  // (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.先判斷這個(gè)call是否被執(zhí)行了，每個(gè)call只能被執(zhí)行一次未状，如果要一個(gè)完成一樣的call可以利用call的clone方法進(jìn)行克隆

2.利用client.dispathcer().execute(this)來進(jìn)行執(zhí)行,其中dispatcher.execute方法為

 synchronized void executed(RealCall call) {
    runningSyncCalls.add(call);
  }

這里我剛開始沒有相同窥妇，之后他加入隊(duì)列后怎么調(diào)用的，后來發(fā)現(xiàn)在 下一個(gè)方法調(diào)用的
3.調(diào)用getResponseWithInterceptorChain函數(shù)來獲取HTTP返回的結(jié)果,這里的originalRequest就是我們的請求剛剛加入隊(duì)列的是RealCall娩践，通過chain.proceed(originalRequest)去調(diào)用

 private 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 (!retryAndFollowUpInterceptor.isForWebSocket()) {
      interceptors.addAll(client.networkInterceptors());
    }
    interceptors.add(new CallServerInterceptor(
        retryAndFollowUpInterceptor.isForWebSocket()));

    Interceptor.Chain chain = new RealInterceptorChain(
        interceptors, null, null, null, 0, originalRequest);
    return chain.proceed(originalRequest);
  }

4.最后還要通知dispathcer自己已經(jīng)執(zhí)行完畢
client.dispatcher().finished(this);
會(huì)執(zhí)行finished（隊(duì)列活翩、call,true）
其中這個(gè)方法是同步和異步都調(diào)用的方法，通過第三個(gè)參數(shù)翻伺，是否執(zhí)行promoteCall方法具體的執(zhí)行會(huì)不同材泄，promoteCall方法

private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
        int runningCallsCount;
        Runnable idleCallback;
        synchronized (this) {
            //TODO calls 移除隊(duì)列
            if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
            //TODO 檢查是否為異步請求，檢查等候的隊(duì)列 readyAsyncCalls吨岭，如果存在等候隊(duì)列拉宗，則將等候隊(duì)列加入執(zhí)行隊(duì)列
            if (promoteCalls) promoteCalls();
            //TODO 運(yùn)行隊(duì)列的數(shù)量
            runningCallsCount = runningCallsCount();
            idleCallback = this.idleCallback;
        }
        //閑置調(diào)用
        if (runningCallsCount == 0 && idleCallback != null) {
            idleCallback.run();
        }
    }
    
    private void promoteCalls() {
        //TODO 檢查 運(yùn)行隊(duì)列 與 等待隊(duì)列
        if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
        if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.

        //TODO 將等待隊(duì)列加入到運(yùn)行隊(duì)列中
        for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
            AsyncCall call = i.next();
            //TODO  相同host的請求沒有達(dá)到最大，加入運(yùn)行隊(duì)列
            if (runningCallsForHost(call) < maxRequestsPerHost) {
                i.remove();
                runningAsyncCalls.add(call);
                executorService().execute(call);
            }

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

B執(zhí)行Enqueue

// RealCall.java
@Override public void enqueue(Callback responseCallback) {
    synchronized (this) { // 如果這個(gè) call 已經(jīng)被執(zhí)行過，拋異常
        if (executed) throw new IllegalStateException("Already Executed");
        executed = true;
    }
    captureCallStackTrace();
    eventListener.callStart(this);
    client.dispatcher().enqueue(new AsyncCall(responseCallback));
}

 //TODO 執(zhí)行異步請求
    synchronized void enqueue(AsyncCall call) {
        //TODO 同時(shí)請求不能超過并發(fā)數(shù)(64,可配置調(diào)度器調(diào)整)
        //TODO okhttp會(huì)使用共享主機(jī)即 地址相同的會(huì)共享socket
        //TODO 同一個(gè)host最多允許5條線程通知執(zhí)行請求
        if (runningAsyncCalls.size() < maxRequests &&
                runningCallsForHost(call) < maxRequestsPerHost) {
            //TODO 加入運(yùn)行隊(duì)列 并交給線程池執(zhí)行
            runningAsyncCalls.add(call);
            //TODO AsyncCall 是一個(gè)runnable旦事，放到線程池中去執(zhí)行魁巩，查看其execute實(shí)現(xiàn)
            executorService().execute(call);
        } else {
            //TODO 加入等候隊(duì)列
            readyAsyncCalls.add(call);
        }
    }