Android Socket连接到服务器但未写入任何内容

Question

I'm currently runing a server on Eclipse(local IP 192.168.1.255, listening to port 4567). A client can connect trought sockets and send messages, that will be printed on the terminal by the server. Part of the server code is the following:

    System.out.println("Client connected: " + clientName);
    String line;

    while (true){
        line = in.nextLine();
        System.out.println("STRING RECEIVED: " + line + " FROM " + clientName);
    }

where in is the input stream of the client socket.

Part of client code, instead, is:

    while(true) {
        System.out.print("\nEnter your input: ");
        line = stdin.next();
        socketOut.println(line);
        socketOut.flush();
    }

So, in example, a possible output on server terminal with two clients connected is the following:

    Client connected: Socket[addr=/192.168.1.225,port=54852,localport=4567]
    STRING RECEIVED: Hello FROM Socket[addr=/192.168.1.225,port=54852,localport=4567]
    STRING RECEIVED: World FROM Socket[addr=/192.168.1.225,port=54852,localport=4567]
    Client connected: Socket[addr=/192.168.1.225,port=54945,localport=4567]
    STRING RECEIVED: Hello2 FROM Socket[addr=/192.168.1.225,port=54945,localport=4567]

Everything works well, so i'm now trying to access server trough sockets on a simple app developed on Android Studio. The code is:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        new BackgroundTask().execute();

    }

    private class BackgroundTask extends AsyncTask {

        @Override
        protected Object doInBackground(Object[] params) {

            try {
                Socket socket = new Socket("10.0.2.2", 4567);
                PrintWriter out = new PrintWriter(socket.getOutputStream());
                out.println(new String("Hi from Android!"));

            } catch (UnknownHostException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            return null;
        }
    }
}

But the output is just

    Client connected: Socket[addr=/192.168.1.225,port=55001,localport=4567]

and nothing else.

Any advice about the println doesn't send anything? The program works perfectly on Eclipse on both client/server side, so i guess the problem is on Android. Also, i enabled the Android network permissions, so the connection should work.

Thanks in advance to everybody.

EDIT : solved, i just changed Android client code to:

            try {
            Socket socket = new Socket("10.0.2.2", 4567);
            if (socket.isConnected()) {
                PrintWriter out = new PrintWriter(new BufferedWriter(
                        new OutputStreamWriter(socket.getOutputStream())), true);
                String line = new String("Hi from Android!");
                out.println(line);
            }

        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

Answer 1

You need to either flush the PrintWriter or construct it to auto-flush. It doesn't by default.