Socket using in a swing applet

Question

I should made a server & client in Java,based on Swing and gui.I neeed to make somehow a socket that will go from the server to the client and from the client to the server, and will pass some kind of a string.I would like to have later a function that would do several things according to the string that would be in the socket.
For some reason I couldn't find a simple example for code that shows how it's done in a simple way.
Anyone has any simple example or can explain how is it being done?

Answer 1

Based on this example, here's a simple network client-server pair using Swing. Note some issues related to correct synchronization: The GUI itself is constructed on the event dispatch thread using invokeLater(). In addition, the code relies on the thread safety of append(). Finally, it incorporates a handy tip from the article Text Area Scrolling.

Update: In Java 7, append() is no longer marked as thread safe; invokeLater() is used in display() to sequence updates.

package net;  import java.awt.*; import java.awt.event.*; import java.io.*; import java.net.*; import java.util.Scanner; import javax.swing.*; import javax.swing.text.DefaultCaret;  /**  * A simple network client-server pair  * @http://stackoverflow.com/questions/3245805  */ public class Echo implements ActionListener, Runnable {      private static final String HOST = "127.0.0.1";     private static final int PORT = 12345;     private final JFrame f = new JFrame();     private final JTextField tf = new JTextField(25);     private final JTextArea ta = new JTextArea(15, 25);     private final JButton send = new JButton("Send");     private volatile PrintWriter out;     private Scanner in;     private Thread thread;     private Kind kind;      public static enum Kind {          Client(100, "Trying"), Server(500, "Awaiting");         private int offset;         private String activity;          private Kind(int offset, String activity) {             this.offset = offset;             this.activity = activity;         }     }      public Echo(Kind kind) {         this.kind = kind;         f.setTitle("Echo " + kind);         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);         f.getRootPane().setDefaultButton(send);         f.add(tf, BorderLayout.NORTH);         f.add(new JScrollPane(ta), BorderLayout.CENTER);         f.add(send, BorderLayout.SOUTH);         f.setLocation(kind.offset, 300);         f.pack();         send.addActionListener(this);         ta.setLineWrap(true);         ta.setWrapStyleWord(true);         DefaultCaret caret = (DefaultCaret) ta.getCaret();         caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);         display(kind.activity + HOST + " on port " + PORT);         thread = new Thread(this, kind.toString());     }      public void start() {         f.setVisible(true);         thread.start();     }      //@Override     public void actionPerformed(ActionEvent ae) {         String s = tf.getText();         if (out != null) {             out.println(s);         }         display(s);         tf.setText("");     }      //@Override     public void run() {         try {             Socket socket;             if (kind == Kind.Client) {                 socket = new Socket(HOST, PORT);             } else {                 ServerSocket ss = new ServerSocket(PORT);                 socket = ss.accept();             }             in = new Scanner(socket.getInputStream());             out = new PrintWriter(socket.getOutputStream(), true);             display("Connected");             while (true) {                 display(in.nextLine());             }         } catch (Exception e) {             display(e.getMessage());             e.printStackTrace(System.err);         }     }      private void display(final String s) {         EventQueue.invokeLater(new Runnable() {             //@Override             public void run() {                 ta.append(s + "\u23CE\n");             }         });     }      public static void main(String[] args) {         EventQueue.invokeLater(new Runnable() {             //@Override             public void run() {                 new Echo(Kind.Server).start();                 new Echo(Kind.Client).start();             }         });     } }