How to Create a Simple Swing-based Java Client-Server Application Using Sockets?

Utilizing sockets in Swing applet

Question

Write a server and client program using Java language based on Swing and GUI. We need to somehow create a socket that goes from the server to the client, and from the client to the server, and be able to pass some kind of string. I hope to write a function later that performs multiple operations based on the string in the socket. For some reason I can't find a simple code example that shows how to achieve this in a simple way. Does anyone have a simple example or can explain how to achieve this?

Answer

Building on this example, here is a simple network client-server pairing using Swing. There are some issues related to correct synchronization to be aware of: The GUI itself is built on the event dispatch thread using invokeLater(). Additionally, this code relies on append() being thread-safe. Finally, I used a handy tip from the article "TextArea Scrolling".

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

[Picture: Echo](https://i.sstatic.net/W32IY.png)

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 {

    // 常量
    private static final String HOST = "127.0.0.1";
    private static final int PORT = 12345;

    // GUI 组件
    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");

    // 网络变量
    private volatile PrintWriter out;
    private Scanner in;
    private Thread thread;

    // 类型枚举
    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;
        // GUI 设置

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