首先在网上搜了下jsp生成验证码的代码，如下：
package com.servlet;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class ValidateCodeServlet extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = 4008416931787800531L;
/**
* Constructor of the object.
*/
public ValidateCodeServlet() {
super();
}
/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
}
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request
* the request send by the client to the server
* @param response
* the response send by the server to the client
* @throws ServletException
* if an error occurred
* @throws IOException
* if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//设置页面不缓存
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
// 在内存中创建图象
int width = 60, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
// 获取绘画对象
Graphics g = image.getGraphics();
// 设定背景色
g.setColor(getRandColor(225, 250));
g.fillRect(0, 0, width, height);
//设定字体
g.setFont(new Font("Times New Roman", Font.BOLD, 20));
// 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
Random random = new Random();
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);
}
// 取随机产生的认证码(4位数字)
String sRand = generateWord();
byte[] cs = sRand.getBytes();
for (int i = 0; i < 4; i++) {
String a = new String(cs, i, 1);
// String rand = String.valueOf(random.nextInt(10));
String rand = a;
// sRand += rand;
// 将认证码显示到图象中
g.setColor(new Color(20 + random.nextInt(110), 20 + 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, 13 * i + 6, 16);
}
// 将认证码存入SESSION
HttpSession session = request.getSession();
session.setAttribute("valicode", sRand);
// 图象生效
g.dispose();
// 输出图象到页面
ImageIO.write(image, "JPEG", response.getOutputStream());
}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
/**
* 给定范围获得随机颜色
* @param fc
* @param bc
* @return
*/
private 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);
}
private String generateWord() {
String[] beforeShuffle = new String[] {"1", "2", "3", "4", "5", "6", "7",
"8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J",
"K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V",
"W", "X", "Y", "Z" };
List list = Arrays.asList(beforeShuffle);
Collections.shuffle(list);
StringBuilder sb = new StringBuilder();
for (int i = 0; i < list.size(); i++) {
sb.append(list.get(i));
}
String afterShuffle = sb.toString();
String result = afterShuffle.substring(5, 9);
return result;
}
}
自己加工了下，原先是产生随机数，这里我就用一个list集合了
然后是在jsp页面中引用这个servlet，如下：
<img id="servletimg" src="<%=path %>/ValidateCodeServlet" flush="true" onclick="reloadImage()" style="vertical-align: bottom;cursor:pointer"></img>
注：cursor:pointer是变手形，reloadImage（）是js方法
function reloadImage(){
document.getElementById('servletimg').src="<%=path %>/ValidateCodeServlet";
}
把相同地址再设置一遍就ok了