socket programming in android app development

Question

This is my Server Program. This works fine. It starts waiting for the client.

package jay.com;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
public class serv {
public static void main(String[] args) throws IOException{
    String recvsentence = null;
    String sendsentence = null;


    ServerSocket server=new ServerSocket(5000);

    System.out.println("waiting for client");

    Socket sock = server.accept();
    System.out.println("Client Connected with IP Address");

    DataInputStream dis = new DataInputStream(sock.getInputStream());

    DataOutputStream dos = new DataOutputStream(sock.getOutputStream());

    recvsentence = dis.readUTF();

    System.out.println("Got Data");

    sendsentence = recvsentence+"changed";

    System.out.println("Message Altered");

    dos.writeUTF(sendsentence);

    sock.close();

    server.close();

}

}

This is my Client Program. Socket is not creating here....

package jay.com;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.net.UnknownHostException;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class Mypro1 extends Activity {
EditText myText,finaltext;
Button button;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    myText=(EditText)findViewById(R.id.editText1);
    button=(Button)findViewById(R.id.button1);
    finaltext=(EditText)findViewById(R.id.editText2);


    button.setOnClickListener(new View.OnClickListener(){

        public void onClick(View arg0) {
            byte adr[] = new byte[4];
            adr[0]=(byte)(192);
            adr[1]=(byte)(168);
            adr[2]=(byte)(1);
            adr[3]=(byte)(141);
            String sendsentence=null;
            String recvsentence=null;
            InetAddress addr=null;      

            try {
                addr = InetAddress.getByName("10.0.2.2");
                //finaltext.setText(addr.toString());
            } catch (UnknownHostException e1) {
                e1.printStackTrace();
            }

            try {
                //finaltext.setText("hi");
                Socket con=new Socket(addr,5000);

                finaltext.setText("Socket Created");

                DataInputStream dis = new DataInputStream(con.getInputStream());
                DataOutputStream dos = new DataOutputStream(con.getOutputStream());

                sendsentence=myText.getText().toString();

                dos.writeUTF(sendsentence);

                System.out.println("waiting for server response");

                recvsentence = dis.readUTF();

                System.out.println("got response");

                finaltext.setText(recvsentence);

            } catch (UnknownHostException e) {
                e.printStackTrace();
            } catch (IOException e) {
                System.out.println("Problem while creating");
                e.printStackTrace();
            }

        }
    });
}

}

Can anyone tell me whats the problem and also i want to know how to run the program. what ip address should i give. whether i've to try to connect to 10.0.2.2 or to 192.168.1.141(my Ip address)....

Answer 1

Sockets are not created on UI thread. They should be created on a separate thread or else would be blocked by the OS. Best approach is to use AysncTask but for a starter,

    new thread(new new Runnable() {
    public void run() {
        // create your socket here.
    }
}).start();

This approach can work.

Answer 2

If you run server client app on emulator, you have to redirect your port otherwise your emulator doesn't work as server - Go through it...

Answer 3

You can find out the IP address of the server by calling server.getInetAddress();

Therefore if you change the line after creating the ServerSocket you will see the current IP address of your server.

System.out.println("waiting for client on IP " + server.getInetAddress());