JSP实现验证码

image.jsp

<%@ page contentType="image/jpeg"%> <%@ page import="java.awt.*"%> <%@ page import="java.awt.image.*"%> <%@ page import="java.util.*"%> <%@ page import="javax.imageio.*"%> <% //在内存中创建图象 int iWidth=130,iHeight=18; BufferedImage image=new BufferedImage(iWidth,iHeight,BufferedImage.TYPE_INT_RGB); //获取图形上下文 Graphics g=image.getGraphics(); //设定背景色 g.setColor(Color.white); g.fillRect(0,0,iWidth,iHeight); //画边框 g.setColor(Color.black); g.drawRect(0,0,iWidth-1,iHeight-1); //取随机产生的认证码(4位数字) String rand=request.getParameter("Rand"); rand=rand.substring(0,rand.indexOf(".")); switch(rand.length()) { case 1:rand="000"+rand;break; case 2:rand="00"+rand;break; case 3:rand="0"+rand;break; default:rand=rand.substring(0,4);break; } //将认证码存入SESSION session.setAttribute("Rand",rand); //将认证码显示到图象中 g.setColor(Color.black); g.setFont(new Font("Times New Roman",Font.PLAIN,18)); g.drawString(rand,10,15); //随机产生88个干扰点,使图象中的认证码不易被其它程序探测到 Random random=new Random(); for(int iIndex=0;iIndex<88;iIndex++) { int x=random.nextInt(iWidth); int y=random.nextInt(iHeight); g.drawLine(x,y,x,y); } //图象生效 g.dispose(); //输出图象到页面 ImageIO.write(image,"JPEG",response.getOutputStream()); //很强大的一句话 %>

输出时应用验证码

 

<script>

document.write("<img border=0 src='/image.jsp?Rand="+Math.random()*10000+" '>");

</script>

<br>
   输认证码:<input name="Rand" maxlength=4 size="10">

<br>

 

登录认证:

 String Rand=request.getParameter("Rand");
 String strRand=(String)session.getAttribute("Rand");
 if(!strRand.equals(Rand))
 
  //未通过;
 }

附注：其实Rand.trim()更好