Not receiving data from Android using TCP connection

Question

I am trying to receive acceleration data from my android phone to my PC.

I have tried using this JAVA code for accessing and sending data from my android:

 import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.TextView;


public class MainActivity extends Activity implements SensorEventListener{

    String mClientMsg = "";
    Thread myCommsThread = null;
    public static final String TAG = "SocketServer";
    private CommsThread commsThread = null;
    TextView tv;
    PrintWriter out;
    private float ax, ay, az;
    private long timenow = 0, timeprev = 0, timestamp =0 ;

    private SensorManager sm;
    private Sensor sensor;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv = (TextView) findViewById(R.id.textView1);
        sm = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        sensor = sm.getSensorList(Sensor.TYPE_LINEAR_ACCELERATION).get(0);
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        sm.registerListener(this, sensor, SensorManager.SENSOR_DELAY_UI);
        this.commsThread = new CommsThread();
        this.myCommsThread = new Thread(this.commsThread);
        this.myCommsThread.start();
    }

    @Override
    protected void onPause() {
        // TODO Auto-generated method stub
        super.onPause();
        sm.unregisterListener(this);
        if (commsThread != null) {
            commsThread.stopComms();
        }
    }

    Handler myHandler = new Handler(){
        public void handleMessage(Message msg){
            TextView status = (TextView) findViewById(R.id.textView3);
            status.setText("Status: Streaming Now!");
        }
    };

    class CommsThread implements Runnable {
        private volatile boolean stopFlag = false;
        private ServerSocket ss = null;
        private static final int SERVERPORT = 6000;
        public void run() {
            Socket s = null;
            try {
                ss = new ServerSocket(SERVERPORT);
            } catch (IOException e) {
                e.printStackTrace();
            }

            try {
                s = ss.accept();
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            myHandler.sendEmptyMessage(0);

            while(!stopFlag){
                try {
                    out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(s.getOutputStream())), true);
                    out.printf("*#%3.2f#%3.2f#%3.2f#%2d#*\n",ax,ay,az,(int)timestamp );
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

        public void stopComms() {
            // TODO Auto-generated method stub
            this.stopFlag = true;
            if(ss != null){
                try {
                    ss.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }

    @Override
    public void onAccuracyChanged(Sensor arg0, int arg1) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        // TODO Auto-generated method stub
        ax = event.values[0];
        ay = event.values[1];
        az = event.values[2];
        timenow = event.timestamp;
        timestamp = (timenow - timeprev)/1000000;
        refreshDisplay();
    }

    private void refreshDisplay() {
        // TODO Auto-generated method stub
        String output = String.format("time: %d -- x:%03.2f | Y:%03.2f | Z:%03.2f", timestamp, ax,ay,az);
        timeprev = timenow;
        tv.setText(output);
    }
}

and this python script as server at my PC:

    import socket
from time import *
import sys

serv=socket.socket()

HOST=''
PORT = 7000 
#HOST="78.91.80.123" //here I use my IP
#ADDR = (HOST,PORT)    
BUFSIZE = 4096   


#bind our socket to the address
try:
    serv.bind((HOST, PORT))
    serv.listen(5)
    conn,addr = serv.accept()
except KeyboardInterrupt:
    print "Keyboard Interrupt"
    serv.close()
    exit(1)
try:
    for i in range(0,3100):
        data=conn.recv(4096)
        sys.stdout.flush()
        chunk=data.split()
        sys.stdout.write("0:%s\n" % chunk[-1]) # writes the last element in the list
        sleep(0.03)

    conn.close()
    sleep(10)

except KeyboardInterrupt:
    conn.close()
    print "bye!"
except IndexError:
    conn.close()
    print "indexError"

I have tested the python script and it works, however when I open the app, Nothing is being sent to the PC. I am kind of new in protocols so i am still trying to figure out what happens.

Answer 1

1. First, you are using two different port numbers. In your Python script, you have PORT = 7000 and in your Java code you have private static final int SERVERPORT = 6000; . These must match in order to create a connection, and make sure you aren't using this port for anything else on your machine.

2. If your Python script is running the server, then you shouldn't use a ServerSocket in your Java code. The ServerSocket waits for incoming connections from a client. To establish a connection to your server, you'd instead want to use:

    Socket s = new Socket("78.91.80.123", SERVERPORT); 

From there, you can write to the socket by viewing some examples in the corresponding Java Documentation.