public class MessengerService extends Service {private static final String TAG = "MessengerService";// 消息处理messengerHandler，处理来自客户端的消息private ServiceMessengerHandler messengerHandler = new ServiceMessengerHandler();// 指向handler的服务端Messengerprivate Messenger mServiceMessenger = new Messenger(messengerHandler);public MessengerService() {}@Overridepublic IBinder onBind(Intent intent) {return mServiceMessenger.getBinder();}public static class ServiceMessengerHandler extends Handler{@Overridepublic void handleMessage(@NonNull Message msg) {super.handleMessage(msg);// 取出客户端的消息内容Bundle clientBundle = msg.getData();String clientMessage = clientBundle.getString("client");Log.i(TAG, "客户端的消息是：" + clientMessage);// 新建一个Message对象,作为回复客户端的对象(Service回复的消息)Message serviceToClientMsg = Message.obtain();Bundle serviceBundle = new Bundle();serviceBundle.putString("service", "你好，客户端很高兴认识你！");serviceToClientMsg.setData(serviceBundle);// 获取客户端携带过来的Messenger对象Messenger mClientMessenger = msg.replyTo;try {// 回复消息给客户端
                mClientMessenger.send(serviceToClientMsg);} catch(RemoteException e) {e.printStackTrace();}}}
}

public class MessengerActivity extends AppCompatActivity implements View.OnClickListener {private static final String TAG = "MessengerActivity";// 客户端的消息处理器private ClientMessengerHandler clientMessengerHandler = new ClientMessengerHandler();// 指向handler的客户端的Messengerprivate Messenger mClientMessenger = new Messenger(clientMessengerHandler);private static class ClientMessengerHandler extends Handler {@Overridepublic void handleMessage(@NonNull Message msg) {super.handleMessage(msg);Bundle serviceBundle = msg.getData();String serviceMessage = serviceBundle.getString("service");Log.i(TAG, "服务端回复的消息是：" + serviceMessage);}}@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_messenger);}public void onClick(View v) {switch (v.getId()) {case R.id.bindService:Intent intent = new Intent(this, MessengerService.class);bindService(intent, mConnection, BIND_AUTO_CREATE);break;case R.id.unBindService:unbindService(mConnection);break;default:break;}}private ServiceConnection mConnection = new ServiceConnection() {@Overridepublic void onServiceConnected(ComponentName componentName, IBinder iBinder) {// 获取服务端关联的Messenger对象Messenger mServiceMessenger = new Messenger(iBinder);// 创建客户端向服务端传递消息的MessageMessage clientToServiceMsg = Message.obtain();Bundle clientBundle = new Bundle();clientBundle.putString("client", "你好，服务器，我是客户端！");clientToServiceMsg.setData(clientBundle);// 在message中添加一个服务端回复客户端的客户端Messenger对象clientToServiceMsg.replyTo = mClientMessenger;try {mServiceMessenger.send(clientToServiceMsg);} catch (RemoteException e) {e.printStackTrace();}}@Overridepublic void onServiceDisconnected(ComponentName componentName) {}};@Overrideprotected void onDestroy() {super.onDestroy();}
}

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".MessengerActivity"><Buttonandroid:id="@+id/bindService"android:layout_width="match_parent"android:layout_height="wrap_content" /><Buttonandroid:id="@+id/unBindService"android:layout_width="match_parent"android:layout_height="wrap_content" /></androidx.constraintlayout.widget.ConstraintLayout>