jsp中验证码的随机选取

时间：2007-09-24 来源：linuxchao

<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,com.sun.image.codec.jpeg.*,java.util.*" %>
<%! //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);
}
%>
<%
//设置页面不缓存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0); out.clear();
// 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
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(); //out.clear();
%>

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