产生4个验证码的ACTION：

————ValidateCodeAction.java————

package org.struts.action;

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

import javax.imageio.ImageIO;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.commons.lang.RandomStringUtils;

public class ValidateCodeAction extends Action {
 public ActionForward execute(ActionMapping mapping, ActionForm form,
   HttpServletRequest request, HttpServletResponse response) {
  try {
   int width = 52;
   int height = 22;
   // 取得一个4位随机字母数字字符串
   String code = RandomStringUtils.random(4, true, true);

   // 保存入session,用于与用户的输入进行比较.
   // 注意比较完之后清除session.
   HttpSession session = request.getSession(true);
   session.setAttribute("code", code);

   response.setContentType("images/jpeg");
   response.setHeader("Pragma", "No-cache");
   response.setHeader("Cache-Control", "no-cache");
   response.setDateHeader("Expires", 0);

   ServletOutputStream out = response.getOutputStream();
   BufferedImage image = new BufferedImage(width, height,
     BufferedImage.TYPE_INT_RGB);
   Graphics g = image.getGraphics();
   // 设定背景色
   g.setColor(getRandColor(200, 250));
   g.fillRect(0, 0, width, height);

   // 设定字体
   Font mFont = new Font("Times New Roman", Font.BOLD, 18);// 设置字体
   g.setFont(mFont);

   // 画边框
   // g.setColor(Color.BLACK);
   // g.drawRect(0, 0, width - 1, height - 1);

   // 随机产生干扰线，使图象中的认证码不易被其它程序探测到
   g.setColor(getRandColor(160, 200));
   // 生成随机类
   Random random = new Random();
   for (int i = 0; i < 155; i++) {
    int x2 = random.nextInt(width);
    int y2 = random.nextInt(height);
    int x3 = random.nextInt(12);
    int y3 = random.nextInt(12);
    g.drawLine(x2, y2, x2 + x3, y2 + y3);
   }

   // 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)));

   g.drawString(code, 2, 16);

   // 图象生效
   g.dispose();
   // 输出图象到页面
   ImageIO.write((BufferedImage) image, "JPEG", out);
   out.close();
  } catch (Exception e) {
   e.printStackTrace();
  }
  return null;
 }

 private 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);
 }

}

struts-config.xml中配置：

 <action  path="/ValidateCode" type="org.struts.action.ValidateCodeAction" /> 

JSP中调用的方法：

<html:img src="/ValidateCode.do" border="0"
    onclick="this.src.value='/ValidateCode.do'"
    alt="请输入此验证码，如看不清请点击刷新。" style="cursor: pointer"/>