实现了大部分聊天功能的代码，带效果图

Client段

 

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import java.text.SimpleDateFormat;
import java.util.*;
import javax.swing.*;

public class ChatClient extends Thread implements ActionListener {
 JFrame jframe = new JFrame("聊天室，客户端");
 JTextArea jta = new JTextArea(10, 30);// 保存聊天信息
 JList list = new JList();// 保存聊天用户列表
 JTextField jtf1 = new JTextField("匿名", 10);
 JLabel lab1 = new JLabel("昵称");
 JTextField jtf2 = new JTextField(10);
 JLabel lab2 = new JLabel("服务器");
 JButton connBtn = new JButton("连接");

 JLabel lab3 = new JLabel("消息");
 JTextField jtf3 = new JTextField(20);// 聊天输入框
 JButton sendBtn = new JButton("发送");
 JCheckBox box = new JCheckBox("启动私聊");
 PrintWriter pw;
 BufferedReader br;
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
 DefaultListModel model = new DefaultListModel();
 Hashtable<String, String> table = new Hashtable<String, String>();// 保存编号和呢称

 public void paint() {
  jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  connBtn.addActionListener(this);
  Container container = jframe.getContentPane();
  JPanel northPanel = new JPanel();
  northPanel.setBackground(Color.YELLOW);
  northPanel.add(lab1);
  northPanel.add(jtf1);
  northPanel.add(lab2);
  northPanel.add(jtf2);
  northPanel.add(connBtn);
  connBtn.setBackground(Color.YELLOW);
  sendBtn.setBackground(Color.GREEN);
  sendBtn.addActionListener(this);
  box.setBackground(Color.GREEN);
  JPanel southPanel = new JPanel();
  southPanel.setBackground(Color.GREEN);
  southPanel.add(box);
  southPanel.add(lab3);
  southPanel.add(jtf3);
  southPanel.add(sendBtn);

  JPanel westPanel = new JPanel(new BorderLayout());
  JLabel userLab = new JLabel("成员列表");
  westPanel.setBackground(Color.RED);
  JScrollPane userPanel = new JScrollPane(list);
  list.setBackground(Color.PINK);
  westPanel.add(userLab, BorderLayout.NORTH);
  westPanel.add(userPanel, BorderLayout.CENTER);
  westPanel.setPreferredSize(new Dimension(100, 480));
  JScrollPane centerPanel = new JScrollPane(jta);
  jta.setBackground(Color.LIGHT_GRAY);
  container.add(northPanel, BorderLayout.NORTH);
  container.add(southPanel, BorderLayout.SOUTH);
  container.add(westPanel, BorderLayout.WEST);
  container.add(centerPanel, BorderLayout.CENTER);

  list.setModel(model);

  jframe.setSize(480, 480);
  jframe.setVisible(true);
 }

 public void actionPerformed(ActionEvent e) {
  String name = e.getActionCommand();
  if (name.equals("连接")) {
   conn();
  } else if (name.equals("发送")) {
   printMessage();
  }
 }

 public void conn() {
  try {
   Socket s = new Socket(jtf2.getText(), 1234);
   connBtn.setEnabled(false);
   pw = new PrintWriter(s.getOutputStream(), true);
   br = new BufferedReader(new InputStreamReader(s.getInputStream()));
   this.start();// 启动接收聊天信息线程
  } catch (UnknownHostException e) {
   jta.append("连接服务器失败,请正确输入服务器地址\n");
  } catch (IOException e) {
   jta.append("连接服务器失败\n");
  }
 }

 public void printMessage() {
  if (pw != null) {
   if (!box.isSelected()) {// 处理正常聊天信息
    Date d = Calendar.getInstance().getTime();
    String fmt = sdf.format(d);
    pw
      .println(fmt + " " + jtf1.getText() + "说 : "
        + jtf3.getText());
    jtf3.setText("");
    pw.flush();
   } else {// 处理私聊信息
    Date d = Calendar.getInstance().getTime();
    User p = (User) list.getSelectedValue();// 得到私聊用户对象
    if (p == null)
     return;
    String fmt = sdf.format(d);// ~代表是私聊的开始 p.getId()代表对谁进行私聊
    pw.println("~" + p.getId() + "~" + "【私聊】" + fmt + " "
      + jtf1.getText() + "对你说 : " + jtf3.getText());
    jta.append("【私聊】" + fmt + " " + "你对【" + p.getName() + "】说 : "
      + jtf3.getText() + "\n");
    jtf3.setText("");
    pw.flush();
   }
  }
 }

 public void run() {
  pw.println("@" + jtf1.getText());
  while (true) {
   try {
    String msg = br.readLine();
    if (msg.startsWith("@")) {// 得到的是用户登陆信息
     String userList[] = msg.split("@");
     table.put(userList[2], userList[1]);// 保存得到的用户编号和呢称
     User p = new User();// 以此编号和呢称创建一个用户
     p.setId(userList[2]);
     p.setName(userList[1]);
     model.addElement(p);// 将用户显示在列表中
     list.setModel(model);

    } else if (msg.startsWith("#")) {// 得到的是用户退出信息
     String userList[] = msg.split("#");
     String id = userList[1];
     User p = new User();
     p.setId(id);// 通过编号创建一个User对象
     model.removeElement(p);// 删除列表中与此编号相同的用户
     list.setModel(model);// 从新显示列表
    } else
     jta.append(msg + "\n");// 正常聊天信息
   } catch (IOException e) {
    jta.append("与服务器断开连接\n");
    break;
   }
  }
 }

 public static void main(String[] args) {
  new ChatClient().paint();
 }
}

 

Sever段

 

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import java.text.SimpleDateFormat;
import java.util.*;
import javax.swing.*;

public class ChatServer implements ActionListener {
 private JFrame jframe = new JFrame("聊天室，服务器");
 JTextArea jta = new JTextArea(10, 20);
 JTextField jtf = new JTextField(20);
 OutputStream os = null;
 PrintWriter pw = null;
 Vector<Socket> v = new Vector<Socket>();//保存所有客户端
 Hashtable<String, String> table = new Hashtable<String, String>();//保存用户编号和呢称
 Hashtable<Socket, String> socketTable = new Hashtable<Socket, String>();//保存客户端和用户编号
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");

 public void paint() {
  Container container = jframe.getContentPane();
  JPanel northPanel = new JPanel();
  JLabel lab1 = new JLabel("系统消息");
  JButton btn = new JButton("发送");
  btn.addActionListener(this);
  northPanel.add(lab1);
  northPanel.add(jtf);
  northPanel.add(btn);

  JScrollPane context = new JScrollPane(jta);
  container.add(northPanel, BorderLayout.NORTH);
  container.add(context);
  jframe.setSize(480, 400);
  jframe.setVisible(true);
  jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  createServer();
 }

 public void createServer() {
  try {
   ServerSocket ss = new ServerSocket(1234);//创建服务器
   jta.append("服务器已经启动\n");
   while (true) {
    Socket s = ss.accept();//等待客户端连接

    os = s.getOutputStream();
    pw = new PrintWriter(os, true);
    new Service(s);//启动与客户端交互的线程
   }
  } catch (IOException e) {
   e.printStackTrace();
  }
 }

 public void actionPerformed(ActionEvent e) {
  writeMessage();//发送系统消息
 }

 public void writeMessage() {//发送系统消息
  Date d = Calendar.getInstance().getTime();
  String fmt = sdf.format(d);
  int size = v.size();// v保存的是所有的客户端
  for (int i = 0; i < size; i++) {
   Socket sk = v.get(i);
   try {
    PrintWriter pw = new PrintWriter(sk.getOutputStream(), true);
    pw.println(fmt + "  系统消息 : " + jtf.getText());
   } catch (IOException e) {
    continue;
   }
  }
  jtf.setText("");
 }

 private class Service extends Thread {
  InputStream is = null;
  InputStreamReader isr = null;
  BufferedReader br = null;
  Socket s;

  public Service(Socket s) {
   try {
    this.s = s;
    is = s.getInputStream();
    isr = new InputStreamReader(is);
    br = new BufferedReader(isr);
   } catch (Exception e) {
    e.printStackTrace();
   }
   this.start();//启动交互线程
  }

  public void run() {
   while (true) {
    try {
     String msg = br.readLine();//读取客户端发送的消息
     sendAll(s, msg);//处理发送的消息
    } catch (IOException e) {
     v.remove(s);
     String id = socketTable.remove(s);
     String name = table.remove(id);
     jta.append("【" + name + "】" + "离开聊天室...");
     jta.append("服务器现在人数为: " + v.size() + "人\n");
     sendAll(s, "#" + id);//处理用户退出消息
     break;
    }
   }
  }

  synchronized public void sendAll(Socket s, String msg) {

   if (msg.startsWith("@")) {//处理用户登陆消息
    String id = System.currentTimeMillis() + "";
    msg = msg + "@" + id;
    String str[] = msg.split("@");
    table.put(id, str[1]);//保存编号和对应的呢称
    socketTable.put(s, id);//保存客户端和对应的编号
    v.add(s);//保存客户端
    jta.append("【" + str[1] + "】" + "进入聊天室...");
    jta.append("服务器现在人数为: " + v.size() + "人\n");
    try {
     PrintWriter pw = new PrintWriter(s.getOutputStream(), true);
     Set<String> set = table.keySet();
     Iterator<String> it = set.iterator();
     while (it.hasNext()) {
      String clientID = it.next();
      pw.println("@" + table.get(clientID) + "@" + clientID);//将登陆消息发给自己
     }
    } catch (IOException e) {
     e.printStackTrace();
    }
    for (int i = 0; i < v.size() - 1; i++) {//将登陆消息发给以前登陆的客户端
     Socket sk = v.get(i);
     try {
      PrintWriter pw = new PrintWriter(sk.getOutputStream(),
        true);
      pw.println(msg);
     } catch (IOException e) {
      continue;
     }
    }
   } else if (msg.startsWith("~")) {//处理私聊信息
    String privateMsg[] = new String[2];
    privateMsg[0] = msg.substring(1, msg.indexOf("~", 1));
    privateMsg[1] = msg.substring(msg.indexOf("~", 1)+1, msg.length());
    String toID = privateMsg[0];//保存的是用户的编号
    Set<Socket> coll = socketTable.keySet();
    Iterator<Socket> it = coll.iterator();
    while (it.hasNext()) {
     Socket id = it.next();
     if (socketTable.get(id).equals(toID)) {//通过客户端找用户的编号
      try {
       PrintWriter pw = new PrintWriter(id
         .getOutputStream(), true);
       pw.println(privateMsg[1]);//如果编号相同则发给此客户端
      } catch (IOException e) {

       e.printStackTrace();
      }
     }
    }
   } else {
    for (int i = 0; i < v.size(); i++) {//处理正常的聊天消息
     Socket sk = v.get(i);
     try {
      PrintWriter pw = new PrintWriter(sk.getOutputStream(),
        true);
      pw.println(msg);
     } catch (IOException e) {
      continue;
     }
    }
   }
  }
 }

 public static void main(String[] args) {
  new ChatServer().paint();
 }
}

 

用来创建用户名称和id

 

public class User {
 private String id;
 private String name;

 public String getId() {
  return id;
 }

 public void setId(String id) {
  this.id = id;
 }

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 public int hashCode() {
  return id.hashCode();
 }

 public boolean equals(Object obj) {
  if (obj == null)
   return false;
  if (!(obj instanceof User))
   return false;
  User user = (User) obj;
  return this.id.equals(user.id);
 }

 public String toString() {
  return this.name;
 }
}