纯数字验证码

登录时常常要用到验证码验证，下面是一个简单的纯数字验证码，详细代码见image.jsp，将每次生成的验证码文本直接存入session中，登录时方便后台从session中取值验证：

<%@ page contentType="image/jpeg"
    import="java.awt.*,
java.awt.image.*,java.util.*,javax.imageio.*"
    pageEncoding="utf-8"%>
<%!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);
    }%>
<%
    out.clear();//这句针对resin服务器，如果是tomacat可以不要这句
    response.setHeader("Pragma", "No-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expires", 0);
    int width = 60, height = 20;
    BufferedImage image = new BufferedImage(width, height,
            BufferedImage.TYPE_INT_RGB);
    Graphics g = image.getGraphics();
    Random random = new Random();
    g.setColor(getRandColor(200, 250));
    g.fillRect(0, 0, width, height);
    g.setFont(new Font("Times New Roman", Font.PLAIN, 18));
    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);
    }
    String sRand = "";
    for (int i = 0; i < 4; i++) {
        String rand = String.valueOf(random.nextInt(10));
        sRand += rand;
        g.setColor(new Color(20 + random.nextInt(110), 20 + random
                .nextInt(110), 20 + random.nextInt(110)));
        g.drawString(rand, 13 * i + 6, 16);
    }
    // 将认证码存入SESSION
    session.setAttribute("sRand", sRand);
    g.dispose();
    ImageIO.write(image, "JPEG", response.getOutputStream());
%>