// 開始執行整個請求
Response getResponseWithInterceptorChain() throws IOException {
  // Build a full stack of interceptors.
 

  // 攔截器棧
  List<Interceptor> interceptors = new ArrayList<>();
  // 前文說過的 普通攔截器
  interceptors.addAll(client.interceptors());
  // 重試攔截器，網路錯誤、請求失敗等
  interceptors.add(retryAndFollowUpInterceptor);
  // 橋接攔截器，主要是重構請求頭即header
  interceptors.add(new BridgeInterceptor(client.cookieJar()));
  // 快取攔截器
 

  interceptors.add(newCacheInterceptor(client.internalCache()));
  // 連線攔截器，連線伺服器，https包裝
  interceptors.add(new ConnectInterceptor(client));
  // 網路攔截器，websockt不支援，同樣是自定義
  if (!forWebSocket) {
    interceptors.addAll(client.networkInterceptors());
  }
  // 服務攔截器，主要是傳送（write、input）、讀取（read、output）資料
  interceptors.add(new
 
 CallServerInterceptor(forWebSocket));

  // 開啟呼叫鏈
  Interceptor.Chain chain = new RealInterceptorChain(
      interceptors, null, null, null, 0, originalRequest);
  return chain.proceed(originalRequest);
}

　// 原始碼路徑 okhttp3/Headers.java

public final class Headers {
  private final String[] namesAndValues;
  // 略
  Builder addLenient(String name, String value) {
    namesAndValues.add(name);
    namesAndValues.add(value.trim());
    return this;
  }
  // 略
 }

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

public interface Call extends Cloneable {
  Request request(); // 獲取請求封裝的資料
  Response execute() throws IOException; // 同步執行
  void enqueue(Callback responseCallback); // 非同步執行
  void cancel(); // 取消請求
  boolean isExecuted();
  boolean isCanceled();
  Call clone();
  interface Factory {
    Call newCall(Request request);
  }
}

// 重點看看中文註釋處即可
final class RealCall implements Call {

  final OkHttpClient client;
  // 重試攔截器
  final RetryAndFollowUpInterceptor retryAndFollowUpInterceptor;

  /** The application's original request unadulterated by redirects or auth headers. */
  final Request originalRequest;
  final boolean forWebSocket;

  // Guarded by this.
  private boolean executed;

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

  @Override public Request request() {
    return originalRequest;
  }

  // 同步執行的實現
  @Override public Response execute() throws IOException {
    // 一個call只能執行一次
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    try {
      // 將請求放在，請求池中執行，此處會立即執行
      client.dispatcher().executed(this);
      // 獲取結果，即執行多個連結器的呼叫鏈
      Response result = getResponseWithInterceptorChain();
      if (result == null) throw new IOException("Canceled");
      return result;
    } finally {
      client.dispatcher().finished(this);
    }
  }

  private void captureCallStackTrace() {
    Object callStackTrace = Platform.get().getStackTraceForCloseable("response.body().close()");
    retryAndFollowUpInterceptor.setCallStackTrace(callStackTrace);
  }

  //  非同步執行，不管行返回結果
  @Override public void enqueue(Callback responseCallback) {
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    // AsyncCall是一個Runnable的實現類，同時一個是RealCall的內部類
    client.dispatcher().enqueue(new AsyncCall(responseCallback));
  }

  @Override public void cancel() {
    retryAndFollowUpInterceptor.cancel();
  }

  @Override public synchronized boolean isExecuted() {
    return executed;
  }

  @Override public boolean isCanceled() {
    return retryAndFollowUpInterceptor.isCanceled();
  }

  @SuppressWarnings("CloneDoesntCallSuperClone") // We are a final type & this saves clearing state.
  @Override public RealCall clone() {
    return new RealCall(client, originalRequest, forWebSocket);
  }

  StreamAllocation streamAllocation() {
    return retryAndFollowUpInterceptor.streamAllocation();
  }

  // 非同步執行的執行緒封裝，Android基本就是這裡了
  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 {
        // 執行呼叫鏈，是不是很重要，哈哈
        Response response = getResponseWithInterceptorChain();
        // 處理回掉
        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);
      }
    }
  }

  /**
   * Returns a string that describes this call. Doesn't include a full URL as that might contain
   * sensitive information.
   */
  String toLoggableString() {
    return (isCanceled() ? "canceled " : "")
        + (forWebSocket ? "web socket" : "call")
        + " to " + redactedUrl();
  }

  String redactedUrl() {
    return originalRequest.url().redact();
  }
	// 最重要的入口了
  	// 最重要的入口了
  	// 最重要的入口了
  // 重要事情說三遍
  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));

    // 脊髓程式碼開始處
    Interceptor.Chain chain = new RealInterceptorChain(
        interceptors, null, null, null, 0, originalRequest);
    return chain.proceed(originalRequest);
  }
}

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

  interface Chain {
    Request request();

    // 管分發,前行
    Response proceed(Request request) throws IOException;

    Connection connection();
  }
}