创建两个Module

在Module：app中的Myservice代码

public class Myservice extends Service {

    @SuppressLint("HandlerLeak")
    Messenger server_messager=new Messenger(new Handler(){
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            //接受客户端消息
            Bundle bundle = msg.getData();
            String message = bundle.getString("client_message");
            Toast.makeText(Myservice.this, "服务器发来的消息："+message, Toast.LENGTH_SHORT).show();
            //向客户端发送消息
            Messenger clientMessager=msg.replyTo;//用于获取客户端的信使
            Message message1 = Message.obtain();
            Bundle bundle1 = new Bundle();
            bundle1.putString("server_message","你不是真正的快乐");
            message1.setData(bundle1);

            try {
                clientMessager.send(message1);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
            super.handleMessage(msg);
        }

    });

    //TODO 返回server_messager的代理人，便于客户端获取服务端信使
    @Override
    public IBinder onBind(Intent intent) {
        return server_messager.getBinder();
    }

    public Myservice() {
    }
    
}

在Module：myservices中的MainActivity代码

public class MainActivity extends AppCompatActivity {
    @SuppressLint("HandlerLeak")
    //3.客户端的信使:负责接受服务器发来的消息
    private Messenger Clientmesssager = new Messenger(new Handler() {
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            Bundle bundle = msg.getData();
            String message = bundle.getString("server_message");
            Toast.makeText(MainActivity.this, "接受到服务器发来的消息" + message, Toast.LENGTH_SHORT).show();
        }
    });
    // 4. 客户端发送消息给服务端
    private Messenger servermessenger;
    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder service) {
            servermessenger = new Messenger(service);
            Message message = Message.obtain();
            Bundle bundle = new Bundle();
            bundle.putString("client_message", "服务器你好");
            message.setData(bundle);
            //非常重要的一句话
            message.replyTo = Clientmesssager;
            try {
                servermessenger.send(message);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {

        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.i("TAG", "onCreate方法");
        //1.绑定服务
        Intent intent = new Intent();
        intent.setAction("com.myf");
        intent.setPackage("com.bwie.mylianxi820");
        bindService(intent,connection, Service.BIND_AUTO_CREATE);
    }

    //2.解除绑定
    @Override
    protected void onDestroy() {
        super.onDestroy();
        unbindService(connection);
    }
}