<%@ page contentType="image/JPEG"  import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"  pageEncoding="GBK"%>
<%!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 < 100; 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("code", sRand);   // 图象生效   g.dispose();   // 输出图象到页面   ImageIO.write(image, "JPEG", response.getOutputStream());
%> 

  <form action="welcome.jsp" method="post" name="loginform">输入验证码：<input type="text" name="authcode" maxlength="4" size="10"><img id="codeimg" name="codeimg" border=0 src="authcode.jsp"><a href="javascript:reloadImage('authcode.jsp')">看不清</a><br/></form> </center><script language="javascript" type="text/javascript">function reloadImage(imgurl){var getimagecode=document.getElementById("codeimg");getimagecode.src= imgurl + "?id=" + Math.random();}</script>