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java – Android TCP Server Client Communication

Posted by: admin June 15, 2020 Leave a comment

Questions:

I found a well written tutorial here for server client communication on android. Works like a charm. But it is only one way communication. I am trying to listen server response in client but not know where I am wrong here. Here is the code for server where I am trying to make changes.

Server

public class Server extends Activity {

    private ServerSocket serverSocket;

    Handler updateConversationHandler;

    Thread serverThread = null;

    private TextView text;



    public static final int SERVERPORT = 8080;

    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        text = (TextView) findViewById(R.id.text2);

        updateConversationHandler = new Handler();

        this.serverThread = new Thread(new ServerThread());
        this.serverThread.start();

    }

    @Override
    protected void onStop() {
        super.onStop();
        try {
            serverSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    class ServerThread implements Runnable {

        public void run() {
            Socket socket = null;
            try {
                serverSocket = new ServerSocket(SERVERPORT);
            } catch (IOException e) {
                e.printStackTrace();
            }
            while (!Thread.currentThread().isInterrupted()) {

                try {

                    socket = serverSocket.accept();

                    CommunicationThread commThread = new CommunicationThread(socket);
                    new Thread(commThread).start();

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

    class CommunicationThread implements Runnable {

        private Socket clientSocket;

        private BufferedReader input;

        public CommunicationThread(Socket clientSocket) {

            this.clientSocket = clientSocket;

            try {

                this.input = new BufferedReader(new InputStreamReader(this.clientSocket.getInputStream()));
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        public void run() {


            while (!Thread.currentThread().isInterrupted()) {

                try {

                    String read = input.readLine();

                     if (read == null ){
                         Thread.currentThread().interrupt();
                     }else{
                         BufferedWriter out = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
                         out.write("TstMsg");
                         updateConversationHandler.post(new updateUIThread(read));

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

    }

    class updateUIThread implements Runnable {
        private String msg;

        public updateUIThread(String str) {
            this.msg = str;
        }

        @Override
        public void run() {
            text.setText("Client Says: "+ msg + new Date() + "\n");

        }

    }

}

Client

public class Client extends Activity {

    private Socket socket;

    private static final int SERVERPORT = 8080;
    private static final String SERVER_IP = "192.168.104.107";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);      
                    new Thread(new ClientThread()).start();

    }


    public void onClick(View view) {
        try {
            EditText et = (EditText) findViewById(R.id.EditText01);
            String str = et.getText().toString();
            PrintWriter out = new PrintWriter(new BufferedWriter(
                    new OutputStreamWriter(socket.getOutputStream())),
                    true);
            out.println(str);
            out.flush();
            BufferedReader  in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String read = in.readLine();
            System.out.println("MSG:" + read);  

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

    class ClientThread implements Runnable {

        @Override
        public void run() {

            try {
                InetAddress serverAddr = InetAddress.getByName(SERVER_IP);
                socket = new Socket(serverAddr, SERVERPORT);

            } catch (UnknownHostException e1) {
                e1.printStackTrace();
            } catch (IOException e1) {
                e1.printStackTrace();
            }

        }

    }
}

Update

When client send any message to server the message is received by server but when server send its response

BufferedWriter out = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
 out.write("TstMsg");

and in client

String read = in.readLine();
System.out.println("MSG:" + read); 

It dose not recieved by client or we can say server listen clients message but client not.
I have added both permissions in manifest.

<uses-permission android:name="android.permission.INTERNET" >
</uses-permission>

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" >
</uses-permission>

Update
After a long hang comes these errors.

11-28 18:35:45.786: E/GTalkService(292): connectionClosed: no XMPPConnection - That's strange!
11-28 18:35:48.806: D/ConnectivityService(148): handleInetConditionHoldEnd: net=1, condition=0, published condition=0
11-28 18:35:54.526: I/GTalkService/c(292): [[email protected]] connect: acct=1000000, state=CONNECTING
11-28 18:35:55.176: D/dalvikvm(1167): GC_CONCURRENT freed 495K, 9% free 6604K/7239K, paused 2ms+3ms
11-28 18:35:55.226: D/Finsky(1167): [1] 5.onFinished: Installation state replication succeeded.
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349): Problem with socket or streams.
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349): java.net.ConnectException: failed to connect to www.google-analytics.com/173.194.39.41 (port 80): connect failed: ETIMEDOUT (Connection timed out)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at libcore.io.IoBridge.connect(IoBridge.java:114)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at java.net.Socket.connect(Socket.java:842)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at com.google.android.apps.analytics.t.run(Unknown Source)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at android.os.Handler.handleCallback(Handler.java:605)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at android.os.Handler.dispatchMessage(Handler.java:92)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at android.os.Looper.loop(Looper.java:137)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at android.os.HandlerThread.run(HandlerThread.java:60)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349): Caused by: libcore.io.ErrnoException: connect failed: ETIMEDOUT (Connection timed out)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at libcore.io.Posix.connect(Native Method)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:85)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  at libcore.io.IoBridge.connect(IoBridge.java:112)
11-28 18:37:18.276: W/GoogleAnalyticsTracker(349):  ... 9 more
11-28 18:37:29.016: D/dalvikvm(349): GC_CONCURRENT freed 1258K, 35% free 8238K/12487K, paused 2ms+8ms
How to&Answers:

readLine() expects an actual line :’ A line is considered to be terminated by any one of a line feed (‘\n’), a carriage return (‘\r’), or a carriage return followed immediately by a linefeed.’

You should therefore send one, eg. with BufferedWriter.newLine().

Answer:

I am still not to sure about what you are trying to achieve. Your error -log shows a XMPPConnection – Error. XMPP isn’t handled over the port you are using in the posted code, so this error message could be either from a different part of your application.
The other error message is related to an HTTP – Connection for Google analytics and neither is related to the code snippet that you posted.
You should downtrace your problem by: catching possible exceptions, Log.d with a tag you can filter your error – messages by.
The hint from Martin James is good I think, so trying to switch to a byte – wise reading of your inputstream at least for verification and downtracing if you receive any data from your server – connection is also a good idea.

Answer:

Have you written the following snippet in your code

out.flush();

after

BufferedWriter out = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
out.write("TstMsg");

Answer:

Have you tried adding a new line ("\n") when trying to write? Try out.write("TstMsg"+ "\n") instead.

Answer:

final Socket s = new Socket();
s.connect(new InetSocketAddress(mHost, mPort), 20000);
final DataOutputStream dos = new DataOutputStream(s.getOutputStream());
dos.write(("This is a message." + "\r\n").getBytes());
dos.flush();

Alternatively:

BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
String outgoingMsg = "This is a message." + System.getProperty("line.separator");
out.write(outgoingMsg);
out.flush();

Answer:

If you are trying to connect to a web server. As far as I know web server handles http protocol and you are trying to connect to a webserver simply with tcp/ip using socket. You will not get expected response as you are violating protocol standard. your option would be if you want to connect to a web server either you use android HttpURLConnection related classes or you create your own application server using severSocket related classes in any programming language to handle your clients.