JSP實現驗證碼

image.jsp

<%@ page contentType="image/jpeg"%> <%@ page import="java.awt.*"%> <%@ page import="java.awt.image.*"%> <%@ page import="java.util.*"%> <%@ page import="javax.imageio.*"%> <% //在內存中創建圖象 int iWidth=130,iHeight=18; BufferedImage image=new BufferedImage(iWidth,iHeight,BufferedImage.TYPE_INT_RGB); //獲取圖形上下文 Graphics g=image.getGraphics(); //設定背景色 g.setColor(Color.white); g.fillRect(0,0,iWidth,iHeight); //畫邊框 g.setColor(Color.black); g.drawRect(0,0,iWidth-1,iHeight-1); //取隨機產生的認證碼(4位數字) 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; } //將認證碼存入SESSION session.setAttribute("Rand",rand); //將認證碼顯示到圖象中 g.setColor(Color.black); g.setFont(new Font("Times New Roman",Font.PLAIN,18)); g.drawString(rand,10,15); //隨機產生88個干擾點,使圖象中的認證碼不易被其它程序探測到 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); } //圖象生效 g.dispose(); //輸出圖象到頁面 ImageIO.write(image,"JPEG",response.getOutputStream()); //很強大的一句話 %>

輸出時應用驗證碼

 

<script>

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

</script>

<br>
   輸認證碼:<input name="Rand" maxlength=4 size="10">

<br>

 

登錄認證:

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

附註：其實Rand.trim()更好