9

I'm developing an Android application (client) and want it to connect with my Java server using TCP communication.

I've done the code - simple program, client send a message and server echos it back - as below:

Server code:

    import java.net.*;


public class Server {

    public static void main(String[] args) {

        int nreq = 1;
        try
        {
            ServerSocket sock = new ServerSocket (8080);
            for (;;)
            {
                Socket newsock = sock.accept();
                System.out.println("Creating thread ...");
                Thread t = new ThreadHandler(newsock,nreq);
                t.start();
            }
        }
        catch (Exception e)
        {
            System.out.println("IO error " + e);
        }
        System.out.println("End!");
    }
}

a Thread Handler code in the same project file of the server:

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

class ThreadHandler extends Thread {
    Socket newsock;
    int n;

    ThreadHandler(Socket s, int v) {
        newsock = s;
        n = v;
    }


    public void run() {
        try {

            PrintWriter outp = new PrintWriter(newsock.getOutputStream(), true);
            BufferedReader inp = new BufferedReader(new InputStreamReader(
                    newsock.getInputStream()));

            outp.println("Hello :: enter QUIT to exit \n");
            boolean more_data = true;
            String line;

            while (more_data) {
                line = inp.readLine();
                System.out.println("Message '" + line + "' echoed back to client.");
                if (line == null) {
                    System.out.println("line = null");
                    more_data = false;
                } else {
                    outp.println("From server: " + line + ". \n");
                    if (line.trim().equals("QUIT"))
                        more_data = false;
                }
            }
            newsock.close();
            System.out.println("Disconnected from client number: " + n);
        } catch (Exception e) {
            System.out.println("IO error " + e);
        }

    }
}

And this is the Client side (Android):

package com.android.client;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;

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

public class Client extends Activity {
    /** Called when the activity is first created. */
    Scanner scanner = new Scanner(System.in);

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

        final EditText msg = (EditText) findViewById(R.id.etMsg);
        Button send = (Button) findViewById(R.id.bSend);
        final TextView convo = (TextView) findViewById(R.id.tvConvo);
        final TextView status = (TextView) findViewById(R.id.tvStatus);

        try {
            send.setOnClickListener(new View.OnClickListener() {

                Socket s = new Socket("localhost", 8080);
                String message = msg.getText().toString();

                @Override
                public void onClick(View v) {
                    status.setText("...");
                    PrintWriter outp = null;
                    BufferedReader inp = null;
                    status.setText("Established connection..");
                    String serverMsg = null;

                    try {
                        outp = new PrintWriter(s.getOutputStream(), true);
                        inp = new BufferedReader(new InputStreamReader(s.getInputStream()));
                        serverMsg = inp.readLine();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    convo.append(serverMsg + "\n");

                    if (message != null) {
                        if (msg.getText().toString().trim() == "QUIT") {
                            try {
                                s.close();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                            status.setText("Disconnected from server.");

                        } else {
                                try {

                                    convo.append(message + "\n");
                                    outp.println(message); 
                                    serverMsg = inp.readLine();
                                    convo.append(serverMsg + "\n");
                                } catch (IOException e) {
                                    e.printStackTrace();
                                }
                        }

                    }
                    else
                        status.setText("Problem in connection..!");
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

And this is the XML file:

<?xml version="1.0" encoding="utf-8" ?> 
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical">
  <TextView android:id="@+id/tvText" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Your message here:" /> 
- <EditText android:id="@+id/etMsg" android:layout_width="match_parent" android:layout_height="wrap_content" android:ems="10">
  <requestFocus /> 
  </EditText>
  <TextView android:id="@+id/tvStatus" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Status..." android:textAppearance="?android:attr/textAppearanceSmall" /> 
  <Button android:id="@+id/bSend" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Send" /> 
  <TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Conversation:" android:textAppearance="?android:attr/textAppearanceLarge" /> 
  <TextView android:id="@+id/tvConvo" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="" /> 
  </LinearLayout>

I tried running it, but nothing happens. When I click the button the TextView doesn't view the "Hello" message from the server.

2
  • Do you have <uses-permission android:name="android.permission.INTERNET" /> set in your manifest.xml? Commented Apr 9, 2012 at 12:53
  • Yes there is an INTERNET permission Commented Apr 9, 2012 at 12:58

2 Answers 2

10

You connect with your Android client to localhost.

Socket s = new Socket("localhost", 8080);

This would only work when your server is running on the Android device. But I think it is running on your PC. So, when you run your app on Android emulator, you can connect to 10.0.2.2 in order to contact the host. On a real device, you have to find out your servers IP address which can be reached by the Android device, e.g. via Wi-Fi.

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2 Comments

Hi Diewie, I'm trying to connect the client (Android) to my PC through the internet, how can I do that? - I tried connecting it through WiFi and it worked by replacing the 10.2.0.0 with my laptop's IP address.
This will only work, when your PC can directly be reached from the Internet or respective port forwarding rules exist. How is your current setup?
0

If your server is on Windows, type cmd in the Start menu search box and then type ipconfig at the command prompt. You will see something like IVP4 Address----- 192.168.0.101. you need to use this address and port number on your client.

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