Java实现局域网QQ，这是最简单的实现了。整个系统只有一个服务器端和一个客户端，成功建立连接后，服务器端发消息给客户端，客户端发消息给服务器端。最上边的文本框是显示接收到的消息的，左边清屏按钮是把接收区域清空的，中间空白的是输入框，右边发送按钮是发送到另一端的，最下面的文本框显示QQ的连接状态。

先来一张图：

源代码-服务器端

package server;import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;public class Server extends JFrame {private JButton b1 = new JButton("发送");private JButton b2 = new JButton("清屏");// 输入框private JTextField text = new JTextField(10);// 显示连接状态private JTextField info = new JTextField(10);// 显示文本框private JTextArea area = new JTextArea(10, 25);private DataInputStream in = null;private DataOutputStream out = null;// 是否和客户端已建立连接标识private boolean connect = false;public static void main(String[] args){Server frame = new Server();frame.setTitle("QQ-服务器端");frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setSize(600, 500);frame.setVisible(true);frame.showInfo("QQ服务器开始启动...");frame.workCycle(frame);}public Server() {// 为b1按钮添加监听事件，“发送”b1.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {if (connect) {String str = text.getText();text.setText(""); // 设置为空Date date = new Date();DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");area.append(format.format(date) + '\n');area.append("我：" + str + '\n');try {out.writeBytes(str + '\n'); // 加上最后的'\n'为了在另一端显示换行} catch (IOException ex) {ex.printStackTrace();}}}});// 为b2按钮添加监听事件，“清屏”b2.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {area.setText("");}});add(BorderLayout.NORTH, new JScrollPane(area));add(BorderLayout.CENTER, text);add(BorderLayout.SOUTH, info);add(BorderLayout.EAST, b1);add(BorderLayout.WEST, b2);}private void showInfo(String str) {info.setText(str);}public void workCycle(Server frame) {try {ServerSocket server = new ServerSocket(60000);Socket socket = server.accept();frame.showInfo("客户端连接成功...");connect = true;in = new DataInputStream(socket.getInputStream());out = new DataOutputStream(socket.getOutputStream());for (;;) { // 始终和客户端连接/*char c = in.readChar();if (c != '\n')area.append("" + c); // (String)c 这样转换竟然不行...elsearea.append("" + '\n');*/String str = in.readLine();Date date = new Date();DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");area.append(format.format(date) + '\n');area.append("client: " + str + '\n');}}catch (IOException ex) {ex.printStackTrace();}}
}

源代码-客户端

package client;import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;public class Client extends JFrame {private JButton b1 = new JButton("发送");private JButton b2 = new JButton("清屏");// 输入框private JTextField text = new JTextField(10);// 显示连接状态private JTextField info = new JTextField(10);// 显示文本框private JTextArea area = new JTextArea(10, 25);private DataInputStream in = null;private DataOutputStream out = null;// 是否和服务器端已建立连接标识private boolean connect = false;public static void main(String[] args){Client frame = new Client();frame.setTitle("QQ-客户端");frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setSize(600, 500);frame.setVisible(true);frame.showInfo("QQ客户端开始启动...");frame.workCycle(frame);}public Client() {// 为b1按钮添加监听事件，“发送”b1.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {if (connect) {String str = text.getText();text.setText(""); // 设置为空Date date = new Date();DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");area.append(format.format(date) + '\n');area.append("我：" + str + '\n');try {out.writeBytes(str + '\n'); // 加上最后的'\n'为了在另一端显示换行} catch (IOException ex) {ex.printStackTrace();}}}});// 为b2按钮添加监听事件，“清屏”b2.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {area.setText("");}});add(BorderLayout.NORTH, new JScrollPane(area));add(BorderLayout.CENTER, text);add(BorderLayout.SOUTH, info);add(BorderLayout.EAST, b1);add(BorderLayout.WEST, b2);}private void showInfo(String str) {info.setText(str);}public void workCycle(Client frame) {try {Socket socket = new Socket("localhost", 60000);frame.showInfo("连接服务器成功...");connect = true;in = new DataInputStream(socket.getInputStream());out = new DataOutputStream(socket.getOutputStream());for (;;) { // 始终和服务器端连接/*char c = in.readChar();if (c != '\n')area.append("" + c); // (String)c 这样转换竟然不行...elsearea.append("" + '\n');*/String str = in.readLine();Date date = new Date();DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");area.append(format.format(date) + '\n');area.append("server: " + str + '\n');}}catch (IOException ex) {ex.printStackTrace();}}
}