javaweb登录验证码的实现方法

@RequestMapping("/user/check.jpg") 
 public void createCode(HttpServletRequest request, HttpServletResponse response) throws IOException { 
  // 通知浏览器不要缓存 
  response.setHeader("Expires", "-1"); 
  response.setHeader("Cache-Control", "no-cache"); 
  response.setHeader("Pragma", "-1"); 
  CaptchaUtil util = CaptchaUtil.Instance(); 
  // 将验证码输入到session中，用来验证 
  String code = util.getString(); 
  request.getSession().setAttribute(“code”, code); 
  // 输出打web页面 
  ImageIO.write(util.getImage(), "jpg", response.getOutputStream()); 
 } 

<img id="img" src="<%=basePath%>user/check.jpg" onclick="refresh()"> 

function refresh() { 
 var url = $("#basePath").val() + "user/check.jpg?number="+Math.random(); 
 $("#img").attr("src",url); 
}

/** 
  * 验证码验证 
  * 
  * @param session 
  * @param code 
  */ 
 private void checkCode(HttpSession session, String code) { 
  String codeSession = (String) session.getAttribute(“code”); 
  if (StringUtils.isEmpty(codeSession)) { 
   log.error("没有生成验证码信息"); 
   throw new IllegalStateException("ERR-01000"); 
  } 
  if (StringUtils.isEmpty(code)) { 
   log.error("未填写验证码信息"); 
   throw new BussinessException("ERR-06018"); 
  } 
  if (codeSession.equalsIgnoreCase(code)) { 
   // 验证码通过 
  } else { 
   log.error("验证码错误"); 
   throw new BussinessException("ERR-06019"); 
  } 
 } 

import java.awt.Color; 
import java.awt.Font; 
import java.awt.Graphics; 
import java.awt.image.BufferedImage; 
import java.util.Random; 
/** 
 * 验证码生成工具 
 * @author HXL 
 * 
 */ 
public class CaptchaUtil { 
 private BufferedImage image;// 图像 
 private String str;// 验证码 
 private static char code[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ123456789".toCharArray(); 
 
 public static final String SESSION_CODE_NAME="code"; 
  
 private CaptchaUtil() { 
  init();// 初始化属性 
 } 
 
 /* 
  * 取得RandomNumUtil实例 
  */ 
 public static CaptchaUtil Instance() { 
  return new CaptchaUtil(); 
 } 
 
 /* 
  * 取得验证码图片 
  */ 
 public BufferedImage getImage() { 
  return this.image; 
 } 
 
 /* 
  * 取得图片的验证码 
  */ 
 public String getString() { 
  return this.str; 
 } 
 
 private void init() { 
  // 在内存中创建图象 
  int width = 85, 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)); 
  // 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(code[random.nextInt(code.length)]); 
   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); 
  } 
  // 赋值验证码 
  this.str = sRand; 
 
  // 图象生效 
  g.dispose(); 
  // ByteArrayInputStream input = null; 
  // ByteArrayOutputStream output = new ByteArrayOutputStream(); 
  // try { 
  // ImageOutputStream imageOut = ImageIO.createImageOutputStream(output); 
  // ImageIO.write(image, "JPEG", imageOut); 
  // imageOut.close(); 
  // input = new ByteArrayInputStream(output.toByteArray()); 
  // } catch (Exception e) { 
  // System.out.println("验证码图片产生出现错误：" + e.toString()); 
  // } 
  // this.image = input 
  this.image = image;/* 赋值图像 */ 
 } 
 
 /* 
  * 给定范围获得随机颜色 
  */ 
 private Color getRandColor(int fc, int bc) { 
  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); 
 } 
}