Struts 验证图片。

package cn.com.lough.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;

/**
 * MyEclipse Struts Creation date: 01-11-2007
 * 
 * XDoclet definition:
 * 
 * @struts.action validate="true"
 */
public class ValidatecodeAction extends Action {
	/*
	 * Generated Methods
	 */

	/**
	 * Method execute
	 * 
	 * @param mapping
	 * @param form
	 * @param request
	 * @param response
	 * @return ActionForward
	 */
	public ActionForward execute(ActionMapping mapping, ActionForm form,
			HttpServletRequest request, HttpServletResponse response) {
		try {
			int width = 50;
			int height = 18;
			// 取得一个4位随机字母数字字符串
			String s = 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("validateCode", s);

			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(s, 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);
	}
}


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

 

问题：点击图片后无法刷新

无法刷新你就在this.src='/validatecode.do'后面加上一个随机数不就好了吗
比如this.src='/validatecode.do?'+random(),我忘记随机数怎么写了 暂时就这么代替了

楼主写得不错，我也有一个检证码的写法，不过是用spring MVC的，参考如下：

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;

public final class ImageCode {

	private static final Random random = new Random();

	private static final Font[] CODEFONT = { new Font("宋体", Font.BOLD, 25), new Font("宋体", Font.BOLD, 25), new Font("宋体", Font.BOLD, 25),
			new Font("宋体", Font.BOLD, 25) };
	private static final Color[] FONTCOLOR = { Color.ORANGE, Color.RED, Color.PINK, Color.BLUE, Color.GREEN };
	private static final Color[] BGCOLOR = { Color.BLACK, Color.WHITE };
	private static final Color LINECOLOR = new Color(242, 234, 22);
	private static final String[] CODE = { "0", "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" };
	private static StringBuffer CONDENUMBER = null;
	private static final int WIDTH = 100, HEIGHT = 25;

	public final String image(HttpServletRequest request, HttpServletResponse response) {
		CONDENUMBER = new StringBuffer();
		BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
		Graphics g = image.getGraphics();
		g.setColor(BGCOLOR[random.nextInt(2)]);
		g.fillRect(0, 0, WIDTH, HEIGHT);
		for (int i = 0; i < 4; i++) {
			drawCode(g, i);
		}
		drawNoise(g, 8);
		g.setColor(Color.gray);
		g.drawRect(0, 0, WIDTH - 1, HEIGHT - 1);
		g.dispose();
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);
		response.setContentType("image/png");
		ServletOutputStream sos = null;
		try {
			sos = response.getOutputStream();
			ImageIO.write(image, "png", sos);
			sos.flush();
			sos.close();
		} catch (Exception e) {
			e.printStackTrace();
			return null;
		}
		return CONDENUMBER.toString();
	}

	private final void drawCode(Graphics graphics, int i) {
		String number = CODE[random.nextInt(36)];
		graphics.setFont(CODEFONT[random.nextInt(4)]);
		graphics.setColor(FONTCOLOR[random.nextInt(5)]);
		graphics.drawString(number, 10 + i * 20, 20);
		CONDENUMBER.append(number);
	}

	private final void drawNoise(Graphics graphics, int lineNumber) {
		graphics.setColor(LINECOLOR);
		int pointX1, pointY1, pointX2, pointY2;
		for (int i = 0; i < lineNumber; i++) {
			pointX1 = 1 + (int) (Math.random() * WIDTH);
			pointY1 = 1 + (int) (Math.random() * HEIGHT);
			pointX2 = 1 + (int) (Math.random() * WIDTH);
			pointY2 = 1 + (int) (Math.random() * HEIGHT);
			graphics.drawLine(pointX1, pointY1, pointX2, pointY2);
		}
	}

}

我比较懒，直接用开源的JCAPTCHA做图片认证。简单方便，而且产生的图片连人都要花时间去辨认，别说用软件了。。

又见session,对扩展一点好处都没有。