private void performSyncHttpRequest() {
  OkHttpClient client = new OkHttpClient();

  Request request = new Request.Builder()
    .url("http://www.baidu.com")
    .build();
  Call call = client.newCall(request);
  Response response = call.execute();
}

  private Handler requestHandler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
      switch (msg.what) {
        case REQUEST_SUCCESS:
          Toast.makeText(MainActivity.this, "SUCCESSFUL", Toast.LENGTH_SHORT).show();
          break;
        case REQUEST_FAIL:
          Toast.makeText(MainActivity.this, "request failed", Toast.LENGTH_SHORT).show();
          break;
        default:
          super.handleMessage(msg);
      }
    }
  };

  private void performSyncHttpRequest() {
    Runnable requestTask = new Runnable() {
      @Override
      public void run() {
        Message msg = requestHandler.obtainMessage();
        try {
          OkHttpClient client = new OkHttpClient();

          Request request = new Request.Builder()
              .url("http://www.baidu.com")
              .build();
          Call call = client.newCall(request);
          // 1
          Response response = call.execute();

          if (!response.isSuccessful()) {
            msg.what = REQUEST_FAIL;
          } else {
            msg.what = REQUEST_SUCCESS;
          }
        } catch (IOException ex) {
          msg.what = REQUEST_FAIL;
        } finally {
          // send the message
          // 2
          msg.sendToTarget();
        }
      }
    };

    Thread requestThread = new Thread(requestTask);
    requestThread.start();
  } 

  private void performAsyncHttpRequest() {
    OkHttpClient client = new OkHttpClient();

    Request request = new Request.Builder()
        .url("http://www.baidu.com")
        .build();
    Call call = client.newCall(request);
    // 1
    call.enqueue(new Callback() {
      // 2
      @Override
      public void onFailure(Call call, IOException e) {
        //Toast.makeText(MainActivity.this, e.getMessage(), Toast.LENGTH_SHORT).show();
        
        if (Looper.getMainLooper().getThread() == Thread.currentThread()) {
          Log.d(TAG, "Main Thread");
        } else {
          Log.d(TAG, "Not Main Thread");
        }
      }

      @Override
      public void onResponse(Call call, final Response response) throws IOException {
        // 3
        if (Looper.getMainLooper().getThread() == Thread.currentThread()) {
          Log.d(TAG, "Main Thread");
        } else {
          Log.d(TAG, "Not Main Thread");
        }
      }
    });
  }  

  MainActivity.this.runOnUiThread(new Runnable() {
    @Override
    public void run() {
      Log.d(TAG, "code: ");
      Toast.makeText(MainActivity.this, String.valueOf(response.code()), Toast.LENGTH_SHORT).show();
    }
  });

MainActivity.this.mView.post(new Runnable() {
  public void run() {
    Log.d("UI thread", "I am the UI thread");
  }
});

private class BackgroundTask extends AsyncTask<String, Void, Bitmap> {
  protected void onPostExecute(Bitmap result) {
    Log.d("UI thread", "I am the UI thread");
  }
}

  public final void runOnUiThread(Runnable action) {
    if (Thread.currentThread() != mUiThread) {
      mHandler.post(action);
    } else {
      action.run();
    }
  }
  // mHandler.post(action); 之post方法的实现
  public final boolean post(Runnable r) {
    return sendMessageDelayed(getPostMessage(r), 0);
  }

  public boolean post(Runnable action) {
    final AttachInfo attachInfo = mAttachInfo;
    if (attachInfo != null) {
      return attachInfo.mHandler.post(action);
    }
    // Assume that post will succeed later
    ViewRootImpl.getRunQueue().post(action);
    return true;
  }

call.enqueue(new Callback() {
  @Override
  public void onFailure(Call call, IOException e) {
    final String errorMMessage = e.getMessage();

    if (Looper.getMainLooper().getThread() == Thread.currentThread()) {
      Log.d(TAG, "Main Thread");
    } else {
      Log.d(TAG, "Not Main Thread");
    }

    MainActivity.this.runOnUiThread(new Runnable() {
      @Override
      public void run() {
        Toast.makeText(MainActivity.this, errorMMessage, Toast.LENGTH_SHORT).show();
      }
    });
  }

  @Override
  public void onResponse(Call call, final Response response) throws IOException {
    if (Looper.getMainLooper().getThread() == Thread.currentThread()) {
      Log.d(TAG, "Main Thread");
    } else {
      Log.d(TAG, "Not Main Thread");
    }

    MainActivity.this.runOnUiThread(new Runnable() {
      @Override
      public void run() {
        Log.d(TAG, "code: ");
        Toast.makeText(MainActivity.this, String.valueOf(response.code()), Toast.LENGTH_SHORT).show();
      }
    });
  }
});