Servlet代码：
public static final int WIDTH=120; public static final int HEIGHT=35; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { BufferedImage image=new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB); Graphics g=image.getGraphics(); //1 设置背景颜色 setBackGround(g); //2 设置边框 setBorder(g); //3 画出干扰线 drawRandomLine(g); //4 写随机数 drawRandomNum((Graphics2D)g); //5 图形写给浏览器 response.setContentType("image/jpeg"); response.setHeader("Expires", "-1"); response.setHeader("Cache-Control", "no-cache"); response.setHeader("Pragma", "no-cache"); ImageIO.write(image, "jpg", response.getOutputStream()); } private void drawRandomNum(Graphics2D g) { g.setColor(Color.RED); g.setFont(new Font("宋体",Font.BOLD,20)); String base = "\u7684\u4e00\u4e86\u662f\u6211\u4e0d\u5728\u4eba\u4eec\u6709\u6765\u4ed6\u8fd9\u4e0a\u7740\u4e2a\u5730\u5230\u5927\u91cc\u8bf4\u5c31\u53bb\u5b50\u5f97\u4e5f\u548c\u90a3\u8981\u4e0b\u770b\u5929\u65f6\u8fc7\u51fa\u5c0f\u4e48\u8d77\u4f60\u90fd\u628a\u597d\u8fd8\u591a\u6ca1\u4e3a"; int x=5; for(int i=0;i<4;i++){ int degree=new Random().nextInt()%30; String ch=base.charAt(new Random().nextInt(base.length()))+""; g.rotate(degree*Math.PI/180, x, 20); g.drawString(ch, x, 20); g.rotate(-degree*Math.PI/180, x, 20); x+=30; } } private void drawRandomLine(Graphics g) { g.setColor(Color.GREEN); for(int i=0;i<5;i++){ int x1=new Random().nextInt(WIDTH); int y1=new Random().nextInt(HEIGHT); int x2=new Random().nextInt(WIDTH); int y2=new Random().nextInt(HEIGHT); g.drawLine(x1, y1, x2, y2); } } private void setBorder(Graphics g) { g.setColor(Color.BLUE); g.drawRect(1, 1, WIDTH-2, HEIGHT-2); } private void setBackGround(Graphics g) { g.setColor(Color.WHITE); g.fillRect(0, 0, WIDTH, HEIGHT); }
jsp代码：
<html> <head> <script> function changeImage(img){ img.src=img.src+"?"+new Date().getTime(); //改变地址 } </script> </head> <body> <form> 用户名：<input type="text" name="username"> <br/> 密码：<input type="text" name="password"> <br/> 认证码：<input type="text" name="checkcode"> <img src="/day07/servlet/ResponseDemo4" onclick="changeImage(this)" alt="换一张" style="cursor:hand"> <br/> <input type="submit" value="注册"> </form> </body> </html>
原文：http://www.cnblogs.com/lyjs/p/4878709.html