图片验证码

总体思路，简单讲，就是后台生成图片同时将图片信息保存在session，前端显示图片，输入验证码信息后提交表单到后台，取出存放在session里的验证码信息，与表单提交的验证码信息核对。

CaptchaUtil是一个工具类，封装了验证码图片生成，和存储session功能。

package com.util;import java.awt.Color;import java.awt.Font;import java.awt.Graphics2D;import java.awt.image.BufferedImage;import java.io.IOException;import java.util.Random;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.sun.image.codec.jpeg.JPEGCodec;import com.sun.image.codec.jpeg.JPEGImageEncoder;/*** @ClassName: CaptchaUtil * @Description: 关于验证码的工具类* @author 无名* @date 2016-5-7 上午8:33:08 * @version 1.0 */public final class CaptchaUtil{    private CaptchaUtil(){}        /*     * 随机字符字典     */    private static final char[] CHARS = { '2', '3', '4', '5', '6', '7', '8',        '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M',        'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };        /*     * 随机数     */    private static Random random = new Random();        /*     * 获取6位随机数     */    private static String getRandomString()    {        StringBuffer buffer = new StringBuffer();        for(int i = 0; i < 6; i++)        {            buffer.append(CHARS[random.nextInt(CHARS.length)]);        }        return buffer.toString();    }        /*     * 获取随机数颜色     */    private static Color getRandomColor()    {        return new Color(random.nextInt(255),random.nextInt(255),                random.nextInt(255));    }        /*     * 返回某颜色的反色     */    private static Color getReverseColor(Color c)    {        return new Color(255 - c.getRed(), 255 - c.getGreen(),- c.getBlue());    }        public static void outputCaptcha(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException     {        response.setContentType("image/jpeg");        String randomString = getRandomString();        request.getSession(true).setAttribute("randomString", randomString);        int width = 100;        int height = 30;        Color color = getRandomColor();        Color reverse = getReverseColor(color);        BufferedImage bi = new BufferedImage(width, height,                BufferedImage.TYPE_INT_RGB);        Graphics2D g = bi.createGraphics();        g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 16));        g.setColor(color);        g.fillRect(0, 0, width, height);        g.setColor(reverse);        g.drawString(randomString, 18, 20);        for (int i = 0, n = random.nextInt(100); i < n; i++)         {            g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);        }        // 转成JPEG格式        ServletOutputStream out = response.getOutputStream();        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);        encoder.encode(bi);        out.flush();    }}

前台调用：

<input type="text" id="captcha" name="captcha" placeholder="验证码" maxlength="10" />              <img id="captchaImage" src="<%=basePath %>login/allowAccess/captcha" onclick="changeImage()"/>

前端JS 点击图片更换验证码

var changeImage = function (){var src=$("#captchaImage")[0].src;src=src+"?timestamp="+(new Date()).valueOf();$('#captchaImage').attr("src", src);}

控制器

@RequestMapping("/allowAccess/loginIndex")public ModelAndView login(HttpServletRequest request, Model model){User session = (User) request.getSession().getAttribute("loginUser");String randomString=(String)request.getSession().getAttribute("randomString");String loginName = request.getParameter("loginName");String passWord = request.getParameter("passWord");String captcha = request.getParameter("captcha");ModelAndView mav = new ModelAndView();System.out.println("randomString:"+randomString);System.out.println("captcha:"+captcha);if(session == null ){if(randomString!=null){if(!randomString.equalsIgnoreCase(captcha)){mav.addObject("NoMsg","11111");mav.setViewName("login");return mav;}}if (TextHelper.isNotNull(loginName) && TextHelper.isNotNull(passWord)) {User loginUser = this.userService.findLoginUser(loginName,passWord);if (loginUser != null) {request.getSession().setAttribute("loginUser", loginUser);mav.setViewName("views/welcome");}else {mav.addObject("NoMsg","222222");mav.setViewName("login");}}else{mav.addObject("NoMsg","333333");mav.setViewName("login");}}else{mav.setViewName("views/index");}return mav;}