验证码的兑现 _Web前端

验证码的实现

<script type="text/javascript" language="javascript"> 
  function changeImg(){ 
   var a=document.getElementById("mySpan"); 
   a.innerHTML='<img align="middle" src="ImageServlet"/> '; //会复盖“mySpan”位置 
  } 
</script> 
 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
  <meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> 
  <title>验证码</title> 
</head> 
<body> 
  <span id="mySpan"><img align="middle" src="ImageServlet" /></span>  
  <a  href="#" onclick="changeImg();">看不清</a> 
</body> 
</html>

public class ImageServlet extends HttpServlet { 
private static final long serialVersionUID = 1L; 
public void doGet(HttpServletRequest request, HttpServletResponse response) 
   throws ServletException, IOException { 
            doPost(request, response); 
} 
public void doPost(HttpServletRequest request, HttpServletResponse response) 
   throws ServletException, IOException { 
  int width=150;//验证码图片宽度 
  int height=60;//验证码图片高度 
  BufferedImage image=new BufferedImage(width,height,BufferedImage.TYPE_3BYTE_BGR); 
  Graphics g=image.getGraphics(); 
  Random random=new Random();//创建一个随机类 
  g.setColor(getRandColor(200,250));//背景颜色要偏淡 
  g.fillRect(0, 0, width, height);//画背景 
  g.setColor(getRandColor(0,255));//边框颜色 
        g.drawRect(0, 0, width-1, height-1);//画边框 
  g.setColor(getRandColor(160,200));// 随机产生5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<8;i++){ 
   int x=random.nextInt(width); 
   int y=random.nextInt(height); 
   int x1=random.nextInt(width); 
   int y1=random.nextInt(height); 
   g.drawLine(x, y, x1, y1); 
  } 
  g.setColor(getRandColor(160,200));// 随机产生100点，使图象中的认证码不易被其它程序探测到 
  for(int i=0;i<100;i++){ 
   int x=random.nextInt(width); 
   int y=random.nextInt(height); 
   g.drawLine(x, y, x, y); 
  } 
        Font font = new Font("Times New Roman", Font.ITALIC,38);  // 创建字体，字体的大小应该根据图片的高度来定。 
        g.setFont(font);//设置字体 
        int length = 6;  // 设置默认生成4个验证码 
  String s="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; // 设置备选验证码:包括"a-z"和数字"0-9" 
  String sRand=""; 
     
        // 用随机产生的颜色将验证码绘制到图像中。 
        // 生成随机颜色(因为是做前景，所以偏深)   
        //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.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));   
  for(int i=0;i<length;i++){ 
   String ch=String .valueOf(s.charAt(random.nextInt(s.length()))); 
   sRand+=ch; 
   g.drawString(ch, 22*i+12, (random.nextInt(5)-2)*i+40); 
  } 
  //将生成的字符串存储在session中 
  HttpSession session=request.getSession();   
  session.setAttribute("checkCode", sRand); 
  g.dispose();//图像生效 
  //禁止图像缓存 
  response.setHeader("Pragma", "No-cache"); 
  response.setHeader("Cache-Control", "no-cache"); 
  response.setDateHeader("Expires", 0);   
  response.setContentType("image/jpeg"); 
  //创建二进制的输出流 
  ServletOutputStream sos=response.getOutputStream(); 
        // 将图像输出到Servlet输出流中。 
        ImageIO.write(image, "jpeg", sos); 
        sos.flush(); 
        sos.close(); 
} 

public Color getRandColor(int lower,int upper){ 
  Random random = new Random(); 
  if(upper>255) 
   upper=255; 
  if(upper<1) 
   upper=1; 
  if(lower<1) 
   lower=1; 
  if(lower>255) 
   lower=255; 
  int r=lower+random.nextInt(upper-lower); 
  int g=lower+random.nextInt(upper-lower); 
  int b=lower+random.nextInt(upper-lower); 
  return new Color(r,g,b); 
} 
}

	<servlet> 
    <servlet-name>ImageServlet</servlet-name> 
    <servlet-class>chenlh.ImageServlet</servlet-class> 
  </servlet> 
   <servlet-mapping> 
    <servlet-name>ImageServlet</servlet-name> 
    <url-pattern>/ImageServlet</url-pattern> 
  </servlet-mapping>

这代码实现的是验证码 ...........????????????