jsp无刷新获取验证码

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code.java 生成验证码

package com.tr.tool;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.Serializable;
import java.util.Random;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* @author wangyun
*
*/
public class ValidateWorld implements Serializable {
private static final long serialVersionUID = 1L;
     Image image = null;
     HttpServletRequest request = null;
     HttpServletResponse response = null;

     public ValidateWorld(HttpServletRequest request, HttpServletResponse response){
         this.request = request;
         this.response = response;
     }

     public Color getRandColor(int fc,int bc){//给定范围获得随机颜色
         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);
     }

     public BufferedImage creatImage(){
          int width=150, height=50;
          //生成随机类
          Random random = new Random();
          BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
          //获取图形上下文
          Graphics g = image.getGraphics();
          // 设定背景色
//          g.setColor(getRandColor(130,200));
          g.fillRect(0,0, width, height);
          //设定字体
          g.setFont(new Font("华文行楷",Font.CENTER_BASELINE,40));

          //画边框
          //g.setColor(getRandColor(200,250));
          //g.drawRect(0,0,width,height);

          // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
//          g.setColor(getRandColor(20,250));

//          for (int i=0;i<70;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);
//
//
//          }
          // 取随机产生的认证码(4位数字)
          //String rand = request.getParameter("rand");
          //rand = rand.substring(0,rand.indexOf("."));
          String str1=randomStr(4);// 得到随机字符
          HttpSession session = request.getSession();
          session.setAttribute("rand",str1);
          g.drawString("    ", 0,0 );
          for (int i=0;i<4;i++ ){
              String rand=str1.substring(i,i+1);
              // 将认证码显示到图象中
              g.setColor(new Color(20+random.nextInt(110),100+random.nextInt(110),20+random.nextInt(110)));
              //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.drawString(rand,25*i+20,40);

          }
          // 图象生效
          g.dispose();
          return image;
     }

   // 得到随机字符
   public String randomStr(int n) {
       String str1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
       String str2 = "";
       int len = str1.length() - 1;
       double r;
       for (int i = 0; i < n; i++ ) {
           r = (Math.random()) * len;
           str2 = str2+str1.charAt((int) r);
       }
       return str2;
   }
}

显示图片也img.jsp

<%@ page language="java" contentType="image/jpeg ; charset=UTF-8"
      pageEncoding="UTF-8" import="java.awt.*,java.awt.image.*,javax.imageio.*,java.io.*"%>
<%@ page import ="com.tr.code"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<%
    response.setHeader("Pragma","No-cache");
     response.setHeader("Cache-Control","no-cache");
     response.setDateHeader("Expires", 0);

     code c = new code(request,response);
     BufferedImage image = c.creatImage();
     OutputStream b = response.getOutputStream();
%>
<%
     ImageIO.write(image, "JPEG", response.getOutputStream());
     //必须添加以下两行否则tomcat下jsp出现getOutputStream() has already been called for this response异常
     out.clear();
     out = pageContext.pushBody();
%>
</body>
</html>

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%
     String path = request.getContextPath();
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script>
     function changeCode()
      {
             document.getElementById("cc").src="<%=path%>/img.jsp?a="+Math.random();
      }
</script>
</head>
<body>
<form action="" method="post">
<table cellspacing="2px" cellpadding="2px" align="center">
<tr>
     <td>用户名：</td>
     <td><input type="text" id="name" value=""/></td>
</tr>
<tr>
     <td>密  码：</td>
     <td><input type="password" id="password" value=""/></td>
</tr>
<tr height="26px">
     <td>验证码：</td><td valign="middle"><input type="text" id="validate"></td>
     <td><a href="#" onclick="changeCode();"><img alt="" border="0" id="cc" src="<%=path %>/img.jsp"/></a></td>
</tr>
<tr>
     <td colspan="2" align="center"><input type="button" name="button" value="submit"/></td>
</tr>
</table>
</form>
</body>
</html>