客户端与服务器之间通过applet进行的通信

Question

i'm relatively new to client-server programming, i'm trying to get simple communication between the client and server on an applet gui, it is working now but i'm getting an exception when I run the client

MODIFIED CODE:

Client:

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

import javax.swing.*;


public class Client extends JApplet{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private JTextArea displayArea;
    private Socket socket = null;
    private DataInputStream input;
    private DataOutputStream output;


    public void init()
    {

        Container container = getContentPane();

        // set up JTextArea to display
        displayArea = new JTextArea();
        displayArea.setEditable(false);
        container.add(new JScrollPane(displayArea), BorderLayout.SOUTH );

        try 
        {
            // make connection
            socket = new Socket(getCodeBase().getHost(), 5423);

            // get streams
            input = new DataInputStream( socket.getInputStream() );
            output = new DataOutputStream( socket.getOutputStream() ); 


            while(true) 
            {
                output.writeUTF("hello from client"); //send message to server
                output.flush(); 

                processMessage(input.readUTF()); //process data from server    
            }
        }
        // catch problems setting up connection and streams
        catch ( IOException ioException ) {
            ioException.printStackTrace(); 
        }

        try 
        {
            input.close();
            output.close();
        } 
        catch (IOException e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }


    // process message received by client
    private void processMessage(String message)
    {
        if (message.equals("hello") ) 
        {
            displayMessage("Connected to server");
        }
    }


    private void displayMessage(final String messageToDisplay)
    {

        SwingUtilities.invokeLater(
                new Runnable() {  

                    public void run() 
                    {
                        displayArea.append(messageToDisplay);
                        displayArea.setCaretPosition(displayArea.getText().length());
                    }
                } 
            ); 
    }

}

Server:

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

import javax.swing.*;


public class Server extends JFrame{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private ServerSocket serverSocket;
    private JTextArea outputArea;
    private Socket socket = null;
    private DataInputStream input;
    private DataOutputStream output;


    public Server()
    {

        super("Server");

        try
        {
            serverSocket = new ServerSocket(5423, 1);
        }
        catch(IOException ioException)
        {
            ioException.printStackTrace();
            System.exit(1);
        }


        outputArea = new JTextArea();
        getContentPane().add(outputArea, BorderLayout.CENTER);
        outputArea.setText("Server awaiting connections\n");


        setSize(300, 300);
        setVisible(true);
    }


    private void doThis() throws IOException
    {
        try
        {
            while(true)
            {

                socket = serverSocket.accept();

                input = new DataInputStream(socket.getInputStream());
                output = new DataOutputStream(socket.getOutputStream());

                output.writeUTF("hello");
                outputArea.append(input.readUTF()); //receive data from client
                output.flush();     
            }
        }
        catch(IOException e)
        {
            e.printStackTrace();
        }
        finally
        {
            output.close();
            input.close();
            socket.close(); //close connection to client
        }
    }


    public static void main(String[] args) throws IOException 
    {
        Server server = new Server();   
        server.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        server.doThis();    
    }
}

Exception reads:

java.net.SocketException: Connection reset at java.net.SocketInputStream.read(Unknown Source) at java.net.SocketInputStream.read(Unknown Source) at java.net.SocketInputStream.read(Unknown Source) at java.io.DataInputStream.readUnsignedShort(Unknown Source) at java.io.DataInputStream.readUTF(Unknown Source) at java.io.DataInputStream.readUTF(Unknown Source) at Client.init(Client.java:45) at sun.applet.AppletPanel.run(Unknown Source) at java.lang.Thread.run(Unknown Source)

Answer 1

Now your Server is at fault.
The ServerSocket should be created once (as it is in your code),
then ServerSocket listener should wait to accept new connections - one per client, it ONLY happens when NEW client attempts to connect,
when NEW client connection is accept()ed a new thread should handle each client and within that thread you should open the IO streams ONCE and then create a loop reading/writing/handling data, again the IO streams should be closed only once AFTER the data handling loop is complete.

Answer 2

tried to take in suggestions posted, there is no exception present this time

Client:

import java.awt.*;
import java.net.*;
import java.io.*;
import javax.swing.*;

public class Client extends JApplet{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private JTextArea displayArea;
    private Socket socket = null;
    private DataInputStream input;
    private DataOutputStream output;

    @Override
    public void init()
    {
        Container container = getContentPane();

        // set up JTextArea to display
        displayArea = new JTextArea();
        displayArea.setEditable(false);
        container.add(new JScrollPane(displayArea), BorderLayout.SOUTH );

        try 
        {   
            // make connection
            socket = new Socket(getCodeBase().getHost(), 8020);

            // get streams
            input = new DataInputStream( socket.getInputStream() );
            output = new DataOutputStream( socket.getOutputStream() ); 

            output.writeUTF("hello from client"); //send message to server  

            processMessage(input.readUTF()); //process data from server     
        }
        // catch problems setting up connection and streams
        catch (IOException e) 
        {
            e.printStackTrace(); 
        }
    }


    // process message received by client
    private void processMessage(String message) throws IOException
    {
        if (message.equals("hello") ) 
        {
            displayMessage("Connected to server");      
        }
    }

    private void displayMessage(final String messageToDisplay)
    {

        SwingUtilities.invokeLater(
                new Runnable() {  

                    public void run() 
                    {
                        displayArea.append(messageToDisplay);
                        displayArea.setCaretPosition(displayArea.getText().length());
                    }
                } 
            ); 
    }

}

Server:

import java.awt.*;
import java.net.*;
import java.io.*;
import javax.swing.*;


public class Server extends JFrame{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private JTextArea outputArea;
    private DataInputStream input;
    private DataOutputStream output;


    public Server()
    {
        super("Server");    

        outputArea = new JTextArea();
        getContentPane().add(outputArea, BorderLayout.CENTER);

        SwingUtilities.invokeLater(
                new Runnable() {  

                    public void run() 
                    {
                        outputArea.setText("Server awaiting connections\n");
                    }
                } 
            ); 


        setSize(300, 300);
        setVisible(true);
    }


    private void doThis() throws IOException
    {
        ServerSocket serverSocket = null;
        Socket socket = null;

        try
        {
            serverSocket = new ServerSocket(8020, 1);
        }
        catch(IOException ioException)
        {
            ioException.printStackTrace();
            System.exit(1);
        }


        try
        {
            while(true)
            {
                socket = serverSocket.accept();

                input = new DataInputStream(socket.getInputStream());
                output = new DataOutputStream(socket.getOutputStream());

                output.writeUTF("hello"); //send a string to client
                outputArea.append(input.readUTF()); //receive data from client and append the string to the text area


            }
        }
        catch(IOException e)
        {
            e.printStackTrace();
        }

        finally 
        {
            socket.close();
        } 
    }


    public static void main(String[] args) 
    {
        new Thread(new Runnable() 
        {
            @Override
            public void run() 
            { 

                Server server = new Server();   
                server.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                try 
                {
                    server.doThis();        
                } 
                catch (IOException e) 
                {
                    e.printStackTrace();
                }   

            }
        }).start();
    }
}