jsp验证码加无刷新更新

JSP做无刷新的验证码：
一共两个页面：
第一个image.jsp
一下是Image.jsp源代码
[java] 
<%@ page language="java" import="java.util.*,java.awt.image.*,java.awt.*,javax.imageio.*" pageEncoding="GBK" contentType="image/jpeg"%> 
<!-- 记得contentType="image/jpeg" --> 
<%! 
Color getRandColor(int start,int end,long seed) 
{ 
    if(start>255) 
    { 
        start=255; 
    } 
    Random random=new Random(seed); 
    int r=start+random.nextInt(end+1-start); 
    int g=start+random.nextInt(end+1-start); 
    int b=start+random.nextInt(end+1-start); 
    return new Color(r,g,b); 
} 
 %> 
<% 
int width=60; 
int height=20; 
//随机产生的验证码中的字母,可以设置多一点 
String[] str={"1","a","A","B","c","2","I","8","U","y"}; 
BufferedImage image=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); 
//这就算是有纸了，需要知道宽度高度 
Graphics g=image.getGraphics(); 
//这就算有笔了 
 
 
 
g.setColor(getRandColor(230,250,System.currentTimeMillis())); 
//这就算把笔蘸上颜色了 
g.fillRect(0,0,width,height); 
//填充底色 
Random random=new Random(System.currentTimeMillis()); 
//画干扰线 
g.setColor(getRandColor(160,200,System.currentTimeMillis())); 
for(int i=0;i<50;i++) 
{ 
    g.drawLine(random.nextInt(6),random.nextInt(15), 
    random.nextInt(6)+random.nextInt(56),random.nextInt(7)+random.nextInt(17)); 
} 
 
 
String check=new String(); 
 
g.setFont(new Font("Times new Roman",Font.PLAIN,18)); 
for(int i=0;i<4;i++) 
{ 
    g.setColor(getRandColor(20,110,System.currentTimeMillis()+i*1000)); 
    //String ran=String.valueOf(random.nextInt(10)); 
    int temp=random.nextInt(10); 
    String ran=str[temp]; 
    check+=ran; 
    g.drawString(ran,6+i*13,16);//分别往上写数字 
} 
//可以通过session来获取随机产生的验证码 
session.setAttribute("check",check); 
 
g.dispose(); 
//使图像生效 
//response.setCharacterEncoding("GBK"); 
//request.setCharacterEncoding("GBK");