验证码的刷新

<%@ page contentType="text/html;charset=GBK"  %>


   
   
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• 验证码：

      
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——>randomNumber.jsp

<%@ page contentType="image/jpeg" pageEncoding="gb2312"
import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"%>



<%!
//给定范围获得随机颜色
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();

//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(getRandColor(160,200));
//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
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
session.setAttribute("rand",sRand);
//图象生效
g.dispose();

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

//ServletOutputStream outStream = response.getOutputStream();
//JPEGImageEncoder encoder =JPEGCodec.createJPEGEncoder(outStream);
//encoder.encode(image);
//outStream.close();

//加上下面两条代码,运行时才不会出现java.lang.IllegalStateException: getOutputStream() has already been called ..........等异常
out.clear();
out = pageContext.pushBody();
%>