validatecode.jsp

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<%@ page pageEncoding="UTF-8"%>
<%@ page contentType="image/jpeg" 
import="java.awt.*,
java.awt.image.*,
java.util.*,
javax.imageio.*" %>
<%!
char[] chars = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 
    'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};
    Color getRandColor(int fc, int bc){//给定范围获得随机颜色
    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);
}
%>
<%
//设置页面不缓存
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);

// 在内存中创建图象
int width = 60, 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));

//画边框
//g.setColor(new Color());
//g.drawRect(0, 0, width-1, height-1);

// 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)
StringBuffer sRand = new StringBuffer();
for (int i = 0; i < 4; i++) {
    String rand = String.valueOf(chars[random.nextInt(26)]);
    sRand.append(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);
}

// 将认证码存入SESSION
session.setAttribute("validateCode", sRand.toString());

// 图象生效
g.dispose();

// 输出图象到页面
ImageIO.write(image, "JPEG", response.getOutputStream());
%>