java 理解如何实现图片验证码傻瓜都能看懂。

先代码后解释：

只要把代码复制到你的项目中就可以了。

代码：

验证码工具类：

package cn.happy.util.imagesVerTion;

/**
 * Author: SamGroves
 *
 * Description: 验证码生成器
 *
 * Date: 2017/8/29
 */
import javax.servlet.http.HttpServletRequest;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.OutputStream;import java.util.HashMap;
import java.util.Map;import java.util.Random;

public class Captcha {
    private static char mapTable[] = {
            '0', '1', '2', '3', '4', '5',
            '6', '7', '8', '9', '0', '1',
            '2', '3', '4', '5', '6', '7',
            '8', '9'};
    public static Map<String, Object> getImageCode(int width, int height, OutputStream os) {
        Map<String,Object> returnMap = new HashMap<String, Object>();//定义了一个集合，
        if (width <= 0) width = 60;
        if (height <= 0) height = 20;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        // 获取图形上下文
        Graphics g = image.getGraphics();
        //生成随机类
        Random random = new Random();
        // 设定背景色
        g.setColor(getRandColor(200, 250));
        g.fillRect(0, 0, width, height);
        //设定字体
        g.setFont(new Font("Times New Roman", Font.PLAIN, 18));
        // 随机产生168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(160, 200));
        for (int i = 0; i < 168; 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);
        }
        //取随机产生的码
        String strEnsure = "";
        //4代表4位验证码,如果要生成更多位的认证码,则加大数值
        for (int i = 0; i < 4; ++i) {
            strEnsure += mapTable[(int) (mapTable.length * Math.random())];
            // 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)));
            // 直接生成
            String str = strEnsure.substring(i, i + 1);
            // 设置随便码在背景图图片上的位置
            g.drawString(str, 13 * i + 20, 25);
        }
        // 释放图形上下文
        g.dispose();
        returnMap.put("image",image);//把验证码的图片放到了map集合中。
        returnMap.put("strEnsure",strEnsure);//把验证码的文字放入到了map集合中。
       /* request.getSession().setAttribute("strEnsure",strEnsure);*/
        System.out.println(strEnsure+"之后的strEnsure");
        return returnMap;
    }
    //给定范围获得随机颜色
    static 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);
    }
}

controller：

  @RequestMapping(value = "/captcha")
    @ResponseBody
    public String imagecode(HttpServletRequest request, HttpServletResponse response) throws Exception {
        response.setDateHeader("Expires", 0);
        response.setHeader("Cache-Control", "no-store, no-cache, must-revalidate");
        response.addHeader("Cache-Control", "post-check=0, pre-check=0");
        response.setHeader("Pragma", "no-cache");
        response.setContentType("image/jpeg");

        OutputStream os = response.getOutputStream();
        //返回验证码和图片的map
        Map<String, Object> map = Captcha.getImageCode(86, 37, os);
        String simpleCaptcha = "simpleCaptcha";
        request.getSession().setAttribute("simpleCaptcha", map.get("strEnsure").toString().toLowerCase());
        request.getSession().setAttribute("codeTime", new Date().getTime());
        try {
            ImageIO.write((BufferedImage) map.get("image"), "jpg", os);
        } catch (IOException e) {
            return "";
        } finally {
            if (os != null) {
                os.flush();
                os.close();
            }
        }
        return null;
    }




        @RequestMapping(value = "/verify")
        @ResponseBody
        public String checkcode(HttpServletRequest request,
                                HttpSession session,
                                String checkCode) throws Exception {

            checkCode=(String) request.getSession().getAttribute("simpleCaptcha");

            // 获得验证码对象
           /* Object cko = session.getAttribute("simpleCaptcha");*/
            String cko = request.getParameter("checkcode01");

            if (cko == null ||cko=="") {
                request.setAttribute("errorMsg", "请输入验证码！");
                System.out.println("验证码是空格的啊");
                return "请输入验证码！";
            }
            String captcha = cko.toString();//文本框输入的验证码
            // 判断验证码输入是否正确
            Date now = new Date();
            Long codeTime = Long.valueOf(session.getAttribute("codeTime") + "");
            if (StringUtils.isEmpty(checkCode) || captcha == null || !(checkCode.equalsIgnoreCase(captcha))) {
                request.setAttribute("errorMsg", "验证码错误！");
                System.out.println("验证码错的呀");
                return "验证码错误，请重新输入！";

                // 验证码有效时长为1分钟

            } else if ((now.getTime() - codeTime) / 1000 / 60 > 1) {
                request.setAttribute("errorMsg", "验证码已失效，请重新输入！");
                System.out.println("验证码时间太长了");
                return "验证码已失效，请重新输入！";
            } else {

                // 在这里可以处理自己需要的事务，比如验证登陆等
                System.out.println("验证码输入正确");
                return "验证通过！";
            }
        }