xwgong

//java代碼
<img src=“路徑.jsp或者action或者servlet” id=“img”/>
<a href="#" onclick="refresh()">看不清？</a>
//js代碼
<script type="text/javascript">
function refresh(){
    document.getElementById("img").src="路徑.jsp？參數="+Math.random（）;
}
</script>

//驗證碼生成頁面
<%@ page  import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>  
<%@ page import="java.io.OutputStream" %>  
<%!  
Color getRandColor(int fc,int bc){  
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);  
}  
%>  
<%  
try{  
response.setHeader("Pragma","No-cache");  
response.setHeader("Cache-Control","no-cache");  
response.setDateHeader("Expires", 0);  
String codelist = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
int width=60, height=20;  
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);  
OutputStream os=response.getOutputStream();  
Graphics g = image.getGraphics();  
Random random = new Random();  
g.setColor(getRandColor(200,250));  
g.fillRect(0, 0, width, height);  
 
g.setFont(new Font("Times New Roman",Font.PLAIN,18));  
g.setColor(getRandColor(160,200));  
for (int i=0;i<155;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);  
}
String sRand="";  
for (int i=0;i<4;i++){  
 int rand=random.nextInt(codelist.length());
    String strRand=codelist.substring(rand,rand+1);
    sRand+=strRand;  
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));  
g.drawString(strRand,13*i+6,16);
}
session.setAttribute("rand",sRand);  
g.dispose();  
 
ImageIO.write(image, "JPEG",os);  
 
os.flush();  
os.close();  
os=null;  
response.flushBuffer();  
out.clear();  
out = pageContext.pushBody();  
}  
catch(IllegalStateException e)  
{  
System.out.println(e.getMessage());  
e.printStackTrace();  
}%>