Creating a simple Hello world Android Client-Server program

Question

To keep it simple, all I'm trying to do is to send a message from my Android Emulator to a Java console server on Eclipse that contains a simple string, then I want the server to reply with another string. Ofcourse; Ill connect to host 10.0.2.2 and use any open port (in my case 4000). The server gets a "connected" msg everytime I click on connecting button on the emulator, but I cant find a way to deliver packets or messages.

In case you want to read some code, here's my (what I think is) too long code for a simple task.

Client package com.example.clienttest;

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

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

public class MainActivity extends Activity {

    Thread m_objThreadClient;
    Socket clientSocket;
    TextView serverMessage;
    EditText clientMessage;
    String sIn, sOut;
    ObjectOutputStream oos;
    ObjectInputStream ois;

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

        serverMessage = (TextView) findViewById(R.id.textView1);
        clientMessage = (EditText) findViewById(R.id.editText1);

    }


    public void Start(View view) throws IOException{
        final String Text;
        String send = " ";
        Text = clientMessage.getText().toString();
        m_objThreadClient = new Thread( new Runnable(){
            public void run()
            {
                try {
                    clientSocket = new Socket("10.0.2.2", 4000);
                    oos = new ObjectOutputStream (clientSocket.getOutputStream());
                    oos.writeObject(Text);
                    oos.flush();

                } catch (IOException e) {
                    serverMessage.setText(e.getMessage());
                }

            }
        });
        serverMessage.setText(send);

        m_objThreadClient.start();

    }

}

and server

import java.net.ServerSocket;
import java.net.Socket;

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;

import java.util.Hashtable;

public class Server2 {

    @SuppressWarnings("resource")
    public static void main (String[] args) throws IOException {

        ServerSocket server = null;  
        try {
            server = new ServerSocket(4000); 
        } catch (IOException e) {
            System.err.println("Could not start up on: " + "4000" + "Maby server is already open? Or a portforwording messup?");
            System.err.println(e);
            System.exit(1);
        }

        Socket client = null;
        while(true) {
            try {
                client = server.accept();
                System.out.print("connected");
            } catch (IOException e) {
                System.err.println("Accept failed.");
                System.err.println(e);
            }

            Thread t = new Thread(new ClientConn(client));
            t.start();
        }
    }
}


class ClientConn implements Runnable {
    private Socket client;
    ObjectInputStream ois;
    ObjectOutputStream oos;

    ClientConn(Socket client) {
        this.client = client;
        try {
            ois = new ObjectInputStream(client.getInputStream());
            String Recv;
            Recv = ois.readLine();

            oos = new ObjectOutputStream(client.getOutputStream());
            oos.writeChars("Welcome");
            oos.flush();

            oos.close();

        } catch (IOException e) {
            System.err.println(e);
            return;
        }
    }

    public void run() {
        String msg, response;
        try {
            System.out.print("checking");
            while ((msg = ois.readLine()) != null) {
                System.out.print(msg);
            }
        } catch (IOException e) {
            System.err.println(e);
        }
    }

    public void sendMsg(String msg) throws IOException {
        oos.writeChars(msg);
    }
}

Thanks~

Answer 1

Some thoughts that may or may not solve the problem:

The method readLine() for the ObjectInputStream is deprecated. Try using a DataInputStream instead. Something like :

try {
        outToClient = new DataOutputStream(socket.getOutputStream());
        inFromClient = new DataInputStream(socket.getInputStream());
} catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
}

And then :

inFromClient.readLine();

Note that the read line will continue to read until it encounters a new line character '\n'. So readLine() will block until it reads a newline.

Try these things and see if they help

EDIT: It appears readLine() for DataInputStream is deprecated as well, but there are several others methods that should work. For example readUTF()