JSP验证码的编写

package com.lasun.platform.util;


import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.util.Random;


import javax.imageio.ImageIO;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


import org.apache.log4j.Logger;


public class AuthimageServlet extends HttpServlet {
/**
* 
*/
private static final long serialVersionUID = 6742001542648779496L;


private static Logger log = Logger.getLogger(AuthimageServlet.class);


public void service(HttpServletRequest request, HttpServletResponse response) {
try {
// 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)
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);
}


// 将认证码存入SESSION
request.getSession().setAttribute("rand", sRand);


// 图象生效
g.dispose();
response.reset();
// 清除掉原来默认的text/html
response.setContentType("image/jpeg");
// 重设为image/jpeg


// 设置页面不缓存
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
// 输出图象到页面
ImageIO.write(image, "JPEG", response.getOutputStream());
} catch (Exception ex) {
log.error("#-----Authimage failed-----#");
log.error(ex);
}
}


private 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);
}
}