如何做验证码功能呢

<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %><%!Color getRandColor(int fc,int bc){//给定范围获得随机颜色        Random random = new Random();        if(fc>255) fc=255;        if(bc>255) bc=255;        int r=fc+random.nextInt(bc-fc);        int g=fc+random.nextInt(bc-fc);        int b=fc+random.nextInt(bc-fc);        return new Color(r,g,b);        }%><%//设置页面不缓存response.setHeader("Pragma","No-cache");response.setHeader("Cache-Control","no-cache");response.setDateHeader("Expires", 0);// 在内存中创建图象int width=60, height=20;BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);// 获取图形上下文Graphics g = image.getGraphics();//生成随机类Random random = new Random();// 设定背景色g.setColor(getRandColor(200,250));g.fillRect(0, 0, width, height);//设定字体g.setFont(new Font("Times New Roman",Font.PLAIN,18));//画边框//g.setColor(new Color());//g.drawRect(0,0,width-1,height-1);// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到g.setColor(getRandColor(160,200));for (int i=0;i<155;i++){int x = random.nextInt(width);int y = random.nextInt(height);        int xl = random.nextInt(12);        int yl = random.nextInt(12);g.drawLine(x,y,x+xl,y+yl);}// 取随机产生的认证码(4位数字)String sRand="";for (int i=0;i<4;i++){    String rand=String.valueOf(random.nextInt(10));    sRand+=rand;    // 将认证码显示到图象中    g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成    g.drawString(rand,13*i+6,16);}// 将认证码存入SESSIONsession.setAttribute("rand",sRand);// 图象生效g.dispose();// 输出图象到页面ImageIO.write(image, "JPEG", response.getOutputStream());%>
------解决方案--------------------------------------------------------
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class JPasswordFieldDemo extends JFrame {
	JTextField username;  //用户名输入框
  JPasswordField password;  //密码输入框
 	JButton logonButton;  //登录按钮
 	JButton cancelButton;  //退出按钮

  public JPasswordFieldDemo() {  //构造函数

  	super("JPasswordField演示");  //调用父类构造函数
  	Container container=getContentPane();  //得到容器
  	container.setLayout(new GridLayout(3, 2, 2, 2));  //设置布局管理器

  	username=new JTextField(16);  //初始化文本输入框,宽度为16列
  	password=new JPasswordField(16);  //初始化密码输入框,宽度为16列
  	logonButton=new JButton("登录");  //初始化登录按钮
  	logonButton.addActionListener(  //登录按钮事件处理
  		new ActionListener(){
     	public void actionPerformed(ActionEvent evt){
     		char[] pw=password.getPassword();  //得到密码
        	String message="您的用户名："+username.getText()+"\n您的密码："+new String(pw);  //消息字符串
  			JOptionPane.showMessageDialog(JPasswordFieldDemo.this, message);  //显示消息
      }
   	});
	   	cancelButton=new JButton("退出");  //初始化退出按钮
	   	cancelButton.addActionListener(  //初始化按钮事件处理
	   		new ActionListener(){
	      	public void actionPerformed(ActionEvent evt){
	            System.exit(0);  //退出程序
	       }
	    });

	   container.add(new JLabel("      用户名:"));  //增加组件
	   container.add(username);
	   container.add(new JLabel("      密码:"));
	  	container.add(password);
	  	container.add(logonButton);
	  	container.add(cancelButton);
	  	setResizable(false);  //不允许用户改变窗口大小
	  	setSize(300,120);  //设置窗口尺寸
	  	setVisible(true);  //设置窗口可视
	  	setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  //关闭窗口时退出程序
  	}

  	public static void main(String[] args) {
  		new JPasswordFieldDemo();