Socket communication between two apps on Android

Question

I have got huge problem with my Android app and I would like to ask you for help.

I am currently writing Android Clietn-Server app using sockets. I have found lots of tutorils on the Internet and from them I have created basics for my project. However, all tutorials are only for one message send and that's all. I need to send more of them so I've been trying to modify it.

This are code fragments responsible for server and client. The rest is not important at this time.

Server:

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        serverStatus = (TextView) findViewById(R.id.server_status);
        recivedMsg = (TextView)findViewById(R.id.rec_msg);

        SERVERIP = getLocalIpAddress();

        Thread fst = new Thread(new ServerThread());
        fst.start();
    }

    public class ServerThread implements Runnable {

        public void run() {
            try {
                if (SERVERIP != null) {
                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            serverStatus.setText("Listening on IP: " + SERVERIP);
                        }
                    });
                    serverSocket = new ServerSocket(SERVERPORT);
                    while (true) {
                        // listen for incoming clients
                        Socket client = serverSocket.accept();
                        handler.post(new Runnable() {
                            @Override
                            public void run() {
                                serverStatus.setText("Connected." + System.getProperty("line.separator"));
                            }
                        });

                        try {
                            line = null;
                            while (connected) {
                                BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
                                if((line = in.readLine())!=null)
                                {
                                    Log.d("ServerActivity", line);
                                    handler.post(new Runnable() {
                                        @Override
                                        public void run() {
                                            if(recivedMsg.equals("CLOSE"))
                                            {
                                                recivedMsg.append("CLOSE socket");
                                                connected = false;
                                            }
                                            else
                                            {
                                                recivedMsg.append("MSG: " + line + System.getProperty("line.separator"));
                                            }
                                            // do whatever you want to the front end
                                            // this is where you can be creative
                                        }
                                    });
                                }
                                else
                                {
                                    recivedMsg.append("empty" + System.getProperty("line.separator"));
                                }
                            }
                            break;
                        } catch (Exception e) {
                            handler.post(new Runnable() {
                                @Override
                                public void run() {
                                    serverStatus.setText("Oops. Connection interrupted. Please reconnect your phones.");
                                }
                            });
                            e.printStackTrace();
                        }
                    }
                } else {
                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            serverStatus.setText("Couldn't detect internet connection.");
                        }
                    });
                }
            } catch (Exception e) {
                handler.post(new Runnable() {
                    @Override
                    public void run() {
                        serverStatus.setText("Error");
                    }
                });
                e.printStackTrace();
            }
        }
    }

Client

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        serverIp = (EditText) findViewById(R.id.server_ip);
        connectPhones = (Button) findViewById(R.id.connect_phones);

        sendField = (EditText) findViewById(R.id.send_field);
        sendMsg = (Button) findViewById(R.id.msg_send);

        connectPhones.setOnClickListener(connectListener);
        sendMsg.setOnClickListener(sendMessage);
    }

    @Override
    protected void onStop() {
         super.onStop();
         try {
                 BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
                 //send output msg
                 String outMsg = "CLOSE"; 
                 out.write(outMsg);
                 out.flush();
                 // make sure you close the socket upon exiting
                 s.close();
         } catch (IOException e) {
                 e.printStackTrace();
         }
    }

    private OnClickListener connectListener = new OnClickListener() {

        @Override
        public void onClick(View v) {
            serverIpAddress = serverIp.getText().toString();
            runTcpConnection();
            sendMessageToServer("Msg");
        }
    };

    private OnClickListener sendMessage = new OnClickListener() {

        @Override
        public void onClick(View v) {
            sendMessageToServer(sendField.getText().toString());
        }
    };

    private void runTcpConnection() {
        try {
            s = new Socket(serverIpAddress, SERVERPORT);
            BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
            //send output msg
            String outMsg = "TCP connecting to " + SERVERPORT + System.getProperty("line.separator"); 
            out.write(outMsg);
            out.flush();
            Log.i("TcpClient", "sent: " + outMsg);
            SystemClock.sleep(10);
            s.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    };

    public void sendMessageToServer(String str) {
        try {
                    s = new Socket(serverIpAddress, SERVERPORT);
                    BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
                    //send output msg
                    String outMsg = str + System.getProperty("line.separator"); 
                    out.write(outMsg);
                    out.flush();
                    Log.i("TcpClient", "sent: " + outMsg);
                    s.close();
                } catch (UnknownHostException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    Log.d("", "hello222");
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    Log.d("", "hello4333");
                }

            }

For now devices connect correctly. Moreover They are sending the first connection messages (those in OnClickListener connectListener ). The problem is that when I am trying to send another message using sendMessageToServer it is impossible. Those messages shows only after client activity is destroyed.

Very interesting is that without SystemClock.sleep(10); listener runTcpConnection() behave strange. Only 'Connected.' displays on server.

Can someone tell me what I have to do to be able to send messages normally?

EDIT: This are things that I have found:

• If I am at the connection sending more messages than all are empty (null) and after the second one connection error shows - please reconnect phones
• If I am at the connection sending more messages without s.close line in sendMessageToServer only one message is passing through. No error is displayed after it.
• The message form runTcpConnection shows always (except when in this function is no SystemClock.sleep(10))

Hope it will help someone to diagnose my error.

Answer 1

As I see, you create a new socket whenever user click button send, right?
I recommend you should init it only one time when user click connect, then you use it in send click event ( because this is TCP, you will disconnect to server if you create new instance of socket)
So, you should remove these lines in sendMessageToServer :

s = new Socket(serverIpAddress, SERVERPORT);
s.close();

and this line in runTcpConnection

s.close();

Socket should close whenever you don't want communicate with the server (onstop is an example, or when change activity...)
Also you should create only one instance of BufferedWriter too.
Hope this help.