//创建OkHttpClient对象
OkHttpClient client = new OkHttpClient();
String run(String url) throws IOException {
   //创建Request请求对象
  Request request = new Request.Builder()
      .url(url)
      .build();
   //创建Call对象，并执行同步获取网络数据
  Response response = client.newCall(request).execute();
  return response.body().string();
}

void runAsync(String url, Callback callback) {
    OkHttpClient client = new OkHttpClient.Builder().addInterceptor(new Interceptor() {
        @Override
        public Response intercept(Chain chain) throws IOException {
            Request request = chain.request();
            Request.Builder builder = request.newBuilder().addHeader("name", "test");
            return chain.proceed(builder.build());
        }
    }).build();
    //创建Request请求对象
    Request request = new Request.Builder()
            .url(url)
            .build();
    client.newCall(request).enqueue(callback);
}

OkhttpClient client = new OkHttpClient
                    .Builder()
                    .connectTimeout(5, TimeUnit.SECONDS)
                    .writeTimeout(10,TimeUnit.SECONDS)
                    .readTimeout(10, TimeUnit.SECONDS)
                    .build();

public final class Request {
  final HttpUrl url;
  final String method;
  final Headers headers;
  final RequestBody body;
  final Object tag;
  private volatile CacheControl cacheControl; // Lazily initialized.
}

@Override public Response execute() throws IOException {
  synchronized (this) {
    if (executed) throw new IllegalStateException("Already Executed");
    executed = true;
  }
  captureCallStackTrace();
  try {
    // 执行 client.dispatcher() 的 executed 方法
    client.dispatcher().executed(this);
    Response result = getResponseWithInterceptorChain();
    if (result == null) throw new IOException("Canceled");
    return result;
  } finally {
    // 最后再执行 dispatcher 的 finish 方法
    client.dispatcher().finished(this);
  }
}

 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);
    return chain.proceed(originalRequest);
  }

  public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
      Connection connection) throws IOException {
     // 省略无关代码
    //  生成 list 当中下一个 interceptot 的 chain 对象
    RealInterceptorChain next = new RealInterceptorChain(
        interceptors, streamAllocation, httpCodec, connection, index + 1, request);
    // 当前的 interceptor
    Interceptor interceptor = interceptors.get(index);
    // 当前的 intercept 处理下一个 intercept 包装的 chain 对象
    Response response = interceptor.intercept(next);
    // ----
    return response;
  }

OkHttpClient client = new OkHttpClient.Builder().addInterceptor(new Interceptor() {
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        Request.Builder builder = request.newBuilder().addHeader("name","test");
        return chain.proceed(builder.build());
    }
}).build();

public final class Dispatcher {
  private int maxRequests = 64;
  private int maxRequestsPerHost = 5;
  private Runnable idleCallback;
  /** Executes calls. Created lazily. */
  private ExecutorService executorService;
  // 异步的请求等待队列
  private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
  // 异步的正在请求的队列
  private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
  // 绒布的正在请求的队列
  private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
}

@Override public void enqueue(Callback responseCallback) {
  synchronized (this) {
    if (executed) throw new IllegalStateException("Already Executed");
    executed = true;
  }
  captureCallStackTrace();
  client.dispatcher().enqueue(new AsyncCall(responseCallback));
}

final class AsyncCall extends NamedRunnable {
  private final Callback responseCallback;
  // ----
  @Override protected void execute() {
    boolean signalledCallback = false;
    try {
      Response response = getResponseWithInterceptorChain();
      // 判断请求是否取消了，如果取消了，直接回调 onFailure
      if (retryAndFollowUpInterceptor.isCanceled()) {
        signalledCallback = true;
        responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
      } else { // 请求成功
        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);
    }
  }
}

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();
}

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