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); 
  } 
}