JSP图片彩色数字验证

产生验证码图片的文件image.jsp
<%@ page contentType="image/jpeg" import="java.awt.*,
java.awt.image.*,java.util.*,javax.imageio.*" %>
<%!
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)
String sRand="";
for (int i=0;i<4;i++