J2EE验证码图片如何生成和点击刷新验证码

package util;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;

public class Verification {
  private static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
  
  /**
   * 生成一个宽为width， 高为height， 验证码为code的图片
   * @param width 图片的宽
   * @param height 图片的高
   * @param code 验证码字符串
   * @return 返回图片验证码
   */
  public static BufferedImage getImage(int width, int height, String code){
    return getImage(width, height, code, 20);
  }
  /**
   * 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt
   * @param width 图片的宽
   * @param height 图片的高
   * @param code 验证码字符串
   * @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整
   * @return 返回图片验证码
   */
  public static BufferedImage getImage(int width, int height, String code, int lineCnt){
    return createImage(width, height, code, lineCnt, 0.01);
  }
  /**
   * 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt
   * 噪声比为noiseRate，即图片中噪音像素点的百分比
   * @param width 图片的宽
   * @param height 图片的高
   * @param code 验证码字符串
   * @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整
   * @param noiseRate 图片中噪音像素点占总像素的百分比
   * @return 返回图片验证码
   */
  public static BufferedImage getImage(int width, int height, String code, int lineCnt, double noiseRate){
    return createImage(width, height, code, lineCnt, noiseRate);
  }
  
  /**
   * 
   * 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt
   * 噪声比为noiseRate，即图片中噪音像素点的百分比
   * @param width 图片的宽
   * @param height 图片的高
   * @param code 验证码字符串
   * @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整
   * @param noiseRate 图片中噪音像素点占总像素的百分比
   * @return 返回图片验证码
   */
  private static BufferedImage createImage(int width, int height, String code, int lineCnt, double noiseRate){
    int fontWidth = ((int)(width * 0.8)) / code.length();
    int fontHeight = (int)(height * 0.7);
    //为了在任意的width和height下都能生成良好的验证码，
    //字体的大小为fontWdith何fontHeight中的小者，
    int fontSize = Math.min(fontWidth, fontHeight);
    //drawString时要用到
    int paddingX = (int) (width * 0.1);
    int paddingY = height - (height - fontSize) / 2;
    
    //创建图像
    BufferedImage buffimg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    //获得画笔
    Graphics g = buffimg.getGraphics();
    //设置画笔的颜色
    g.setColor(getRandColor(200, 255));
    //然后填充一个矩形，即设置背景色
    g.fillRect(0, 0, width, height);
    
    // 设置干扰线
    for (int i = 0; i < lineCnt; i++) {
        //随机获取干扰线的起点和终点
      int xs = (int)(Math.random() * width);
      int ys = (int)(Math.random() * height);
      int xe = (int)(Math.random() * width);
      int ye = (int)(Math.random() * height);
      g.setColor(getRandColor(1, 255));
      g.drawLine(xs, ys, xe, ye);
    }
    // 添加噪点
    int area = (int) (noiseRate * width * height);
    for(int i=0; i<area; ++i){
        int x = (int)(Math.random() * width);
        int y = (int)(Math.random() * height);
        buffimg.setRGB(x, y, (int)(Math.random() * 255));
    }
    //设置字体
    Font font = new Font("Ravie", Font.PLAIN, fontSize);
    g.setFont(font);
    
    for(int i=0; i<code.length(); ++i){
        String ch = code.substring(i, i+1);
        g.setColor(getRandColor(1, 199));
        g.drawString(ch, paddingX + fontWidth * i, paddingY);
    }
    return buffimg;
    
  }
  /**
   * 获取随机的颜色，r,g,b的取值在L到R之间
   * @param L 左区间
   * @param R 右区间
   * @return 返回随机颜色值
   */
  private static Color getRandColor(int L, int R){
    if(L > 255)
      L = 255;
    if(R > 255)
      R = 255;
    if(L < 0)
      L = 0;
    if(R < 0)
      R = 0;
    int interval = R - L; 
    int r = L + (int)(Math.random() * interval);
    int g = L + (int)(Math.random() * interval);
    int b = L + (int)(Math.random() * interval);
    return new Color(r, g, b);
  }

  /**
   * 随机生成若干个由大小写字母和数字组成的字符串
   * @param len 随机生成len个字符
   * @return 返回随机生成的若干个由大小写字母和数字组成的字符串
   */
  public static String getRandCode(int len){
    String code = "";
    for(int i=0; i<len; ++i){
      int index = (int)(Math.random() * ALPHABET.length());
      code = code + ALPHABET.charAt(index);
    }
    return code;
  }
  /**
   * 将图片转为byte数组
   * @param image 图片
   * @return 返回byte数组
   * @throws IOException
   */
  public static byte[] getByteArray(BufferedImage image) throws IOException{
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ImageIO.write(image, "png", baos);
    return baos.toByteArray();
    //ByteArrayOutputStream 不需要close
    
  }
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    HttpSession session = request.getSession();
    //随机生成字符串，并写入session
    String code = Verification.getRandCode(4);
    session.setAttribute("verification", code);
    BufferedImage image = util.Verification.getImage(100,30, code, 5);
    response.setContentType("image/png");
    
    OutputStream out = response.getOutputStream();
    out.write(util.Verification.getByteArray(image));
    out.flush();
    out.close();
    
  }
 

<%@page import="util.Verification"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
  pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>Insert title here</title>

<script type="text/javascript">
    function refreshcode(){
      document.getElementById("verification").src= "/verificationCode/verificationCode?hehe="+Math.random();
    }
  </script>
</head>
<body>
  
  <form action="<%=request.getContextPath()+"/checkVerification" %>" method="post">
    验证码:<input type="text" name="submitVerification">
    <img id="verification" alt="" title="看不清点击刷新验证码" src="<%=request.getContextPath()+"/verificationCode" %>"
    onclick="refreshcode()"><br>
    <input type="submit" name="submit" value="提交">
  </form>
  
</body>
</html>

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  HttpSession session = request.getSession();
  String verification = (String)session.getAttribute("verification");
  String submitVerification = request.getParameter("submitVerification");
  PrintWriter out = response.getWriter();
  if(verification!=null && submitVerification!=null){
   if(verification.toLowerCase().equals(submitVerification.toLowerCase())){
    out.println("yes!!!");
   }
   else{
    out.println("no!!!");
   }
   
  }
  else{
   out.println("no!!!");
  }
  session.removeAttribute("verification");//防止用户重复提交表单

 }

 /**
  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
  doGet(request, response);
 }