Using Sockets to send and receive data

Question

I am using sockets to connect my Android application (client) and a Java backend Server. From the client I would like to send two variables of data each time I communicate w

Answer 1

    //Client

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

    public class Client {
        public static void main(String[] args) {

        String hostname = "localhost";
        int port = 6789;

        // declaration section:
        // clientSocket: our client socket
        // os: output stream
        // is: input stream

            Socket clientSocket = null;  
            DataOutputStream os = null;
            BufferedReader is = null;

        // Initialization section:
        // Try to open a socket on the given port
        // Try to open input and output streams

            try {
                clientSocket = new Socket(hostname, port);
                os = new DataOutputStream(clientSocket.getOutputStream());
                is = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            } catch (UnknownHostException e) {
                System.err.println("Don't know about host: " + hostname);
            } catch (IOException e) {
                System.err.println("Couldn't get I/O for the connection to: " + hostname);
            }

        // If everything has been initialized then we want to write some data
        // to the socket we have opened a connection to on the given port

        if (clientSocket == null || os == null || is == null) {
            System.err.println( "Something is wrong. One variable is null." );
            return;
        }

        try {
            while ( true ) {
            System.out.print( "Enter an integer (0 to stop connection, -1 to stop server): " );
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            String keyboardInput = br.readLine();
            os.writeBytes( keyboardInput + "\n" );

            int n = Integer.parseInt( keyboardInput );
            if ( n == 0 || n == -1 ) {
                break;
            }

            String responseLine = is.readLine();
            System.out.println("Server returns its square as: " + responseLine);
            }

            // clean up:
            // close the output stream
            // close the input stream
            // close the socket

            os.close();
            is.close();
            clientSocket.close();   
        } catch (UnknownHostException e) {
            System.err.println("Trying to connect to unknown host: " + e);
        } catch (IOException e) {
            System.err.println("IOException:  " + e);
        }
        }           
    }





//Server




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

public class Server1 {
    public static void main(String args[]) {
    int port = 6789;
    Server1 server = new Server1( port );
    server.startServer();
    }

    // declare a server socket and a client socket for the server

    ServerSocket echoServer = null;
    Socket clientSocket = null;
    int port;

    public Server1( int port ) {
    this.port = port;
    }

    public void stopServer() {
    System.out.println( "Server cleaning up." );
    System.exit(0);
    }

    public void startServer() {
    // Try to open a server socket on the given port
    // Note that we can't choose a port less than 1024 if we are not
    // privileged users (root)

        try {
        echoServer = new ServerSocket(port);
        }
        catch (IOException e) {
        System.out.println(e);
        }   

    System.out.println( "Waiting for connections. Only one connection is allowed." );

    // Create a socket object from the ServerSocket to listen and accept connections.
    // Use Server1Connection to process the connection.

    while ( true ) {
        try {
        clientSocket = echoServer.accept();
        Server1Connection oneconnection = new Server1Connection(clientSocket, this);
        oneconnection.run();
        }   
        catch (IOException e) {
        System.out.println(e);
        }
    }
    }
}

class Server1Connection {
    BufferedReader is;
    PrintStream os;
    Socket clientSocket;
    Server1 server;

    public Server1Connection(Socket clientSocket, Server1 server) {
    this.clientSocket = clientSocket;
    this.server = server;
    System.out.println( "Connection established with: " + clientSocket );
    try {
        is = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        os = new PrintStream(clientSocket.getOutputStream());
    } catch (IOException e) {
        System.out.println(e);
    }
    }

    public void run() {
        String line;
    try {
        boolean serverStop = false;

            while (true) {
                line = is.readLine();
        System.out.println( "Received " + line );
                int n = Integer.parseInt(line);
        if ( n == -1 ) {
            serverStop = true;
            break;
        }
        if ( n == 0 ) break;
                os.println("" + n*n ); 
            }

        System.out.println( "Connection closed." );
            is.close();
            os.close();
            clientSocket.close();

        if ( serverStop ) server.stopServer();
    } catch (IOException e) {
        System.out.println(e);
    }
    }
}