<%@ page language="java" pageEncoding="gbk"%> <%@ 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++){     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());  out.clear(); %>

<td width="62" valign="bottom"><div align="left"><img name="img" id="img" border=0 src="index/image.jsp" onclick="this.src='index/image.jsp?'+Math.random();" /></div></td>

this.src='index/image.jsp?'+Math.random();

        String randb = (String) request.getSession().getAttribute("rand");