JavaWeb用户信息管理系统-在登录中添加验证码功能

@WebServlet("/validateCode.do")
public class ValidateCodeServlet extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    // 在内存中创建图象
    int width = 70, height = 45;
    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, 20));
    // 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);
    }
    // 图象生效
    g.dispose();
    try {
      ImageIO.write(image, "JPEG", response.getOutputStream());
    } catch (Exception e) {
      System.out.println("验证码图片产生出现错误：" + e.toString());
    }
    //保存验证码到Session
    request.getSession().setAttribute(Constants.VALIDATE_CODE_KEY, sRand);
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    this.doGet(request, response);
  }
  /*
   * 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);
  }
}

<span>
<input name="code" type="text" value="验证码" onclick="JavaScript:this.value=''"/>
</span>
<cite>
<img id="code" src="validateCode.do" onclick="change()">
</cite>

if(uri.indexOf("login.jsp") != -1 || uri.indexOf("login.do") != -1|| uri.indexOf("validateCode.do") != -1)