Question

I am testing socket programming on Android however I am having a problem. The client is basically launched through the main activity with a basic function of sending a message to the server and getting a reply.

the client activity:

package com.test.socket;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;

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

public class socketActivity extends Activity implements OnClickListener {

String input;
private EditText et;
private ObjectOutputStream oos;
private TextView tv;
private String message;
private ObjectInputStream ois;

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

    try{

        InetAddress host = InetAddress.getLocalHost();
        Socket socket = new Socket(host.getHostName(),7777);
        //send to server

        oos = new ObjectOutputStream(socket.getOutputStream());

        et = (EditText) findViewById(R.id.text);
        Button sendButton = (Button) findViewById(R.id.button);
        sendButton.setOnClickListener(this);

        //read from server
        ois = new ObjectInputStream(socket.getInputStream());


        //System.out.println("Message from Server: "+message);
        tv = (TextView) findViewById(R.id.textView);

    }

    catch(UnknownHostException e)
    {
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}


@Override
public void onClick(View v) {
    // TODO Auto-generated method stub
    switch(v.getId())
    {
    case R.id.button:
        input = et.getText().toString();
        try {
            oos.writeObject(input);
            ois.close();
            oos.close();
            message = (String) ois.readObject();
            tv.setText("Message from Server: "+message);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        break;
    }
}



}

The Server class launched separately from JCreator listening to port 7777:

import java.io.*;
import java.lang.*;
import java.net.*;

public class server {

private ServerSocket server;
private int port = 7777;

public server()
{
    try{
        server = new ServerSocket(port);
    }
    catch(IOException e)
    {
        e.printStackTrace();
    }


}

public static void main(String args[])
{
    server example = new server();
    example.handleConnection();
}

public void handleConnection()
{
    System.out.println("Waiting for client message...");

    while(true)
    {
        try{
            Socket socket = server.accept();
            new ConnectionHandler(socket);
        }
        catch(IOException e)
        {
            e.printStackTrace();
        }
    }
}

}

ConnectionHandler class which the Server accesses:

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;


public class ConnectionHandler implements Runnable {

private Socket socket;

public ConnectionHandler(Socket socket)
{
    this.socket = socket;

    Thread t = new Thread(this);
    t.start();
}

@Override
public void run() {
    // TODO Auto-generated method stub
    try{

        //receive from client
        ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
        String message = (String) ois.readObject();

        System.out.println("Message from client: "+message);

        if(message.equals("check"))
        {
            System.out.println("Checking for malicious interference...");
            Thread.sleep(5000);
            System.out.println("Status: Files are good.");
        }

        //send response to client
        ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());


        if(message.equals("check"))
        {
            oos.writeObject("Checking...");
        }

        else oos.writeObject("Invalid input");



        ois.close();
        oos.close();
        socket.close();

        System.out.println("Waiting for client message...");
    }
    catch(IOException e)
    {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}
}

I have tested the code on JCreator and Eclipse through Java application not Android app and it worked perfect. However when I try doing it through the activity, it’s not working.

Any ideas?

Answer 1

In Android, localhost would point to the phone/emulator itself. It doesn’t point to your server. The following line below is pointing to your Android device/emulator and not your server. You need to get the actual IP of the server to get it working from your Android

    InetAddress host = InetAddress.getLocalHost();
    Socket socket = new Socket(host.getHostName(),7777);

It works through Java App, because when you execute it from the context of Java Application, the localhost is pointing to the same server location.