下面imagecode方法是一个生成图形验证码的请求，checkcode方法实现了对这个图形验证码的验证。从验证码的生成到验证的过程中，验证码是通过Session来保存的，并且设定一个验证码的最长有效时间为5分钟。验证码的生成规则是从0~9的数字中，随机产生一个4位数，并增加一些干扰元素，最终组合成为一个图形输出

1、验证码生成类

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 ImageCode {
    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>();
        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);
            g.drawString(str, 13 * i + 6, 16);
        }
        // 释放图形上下文
        g.dispose();
        returnMap.put("image",image);
        returnMap.put("strEnsure",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);
    }
}

2、获取验证码API

@RequestMapping(value = "/images/imagecode")
public String imagecode(HttpServletRequest request, HttpServletResponse response) throws Exception {
    OutputStream os = response.getOutputStream();
    Map<String,Object> map = ImageCode.getImageCode(60, 20, 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"), "JPEG", os);
    } catch (IOException e) {
        return "";
    }
    return null;
}

3、验证验证码API

@RequestMapping(value = "/checkcode")
@ResponseBody
public String checkcode(HttpServletRequest request, HttpSession session) throws Exception {
    String checkCode = request.getParameter("checkCode");
    Object cko = session.getAttribute("simpleCaptcha") ; //验证码对象
    if(cko == null){
        request.setAttribute("errorMsg", "验证码已失效，请重新输入！");
        return "验证码已失效，请重新输入！";
    }
    String captcha = cko.toString();
    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！");
        return "验证码错误！";
    } else if ((now.getTime()-codeTime)/1000/60>5) {
        //验证码有效时长为5分钟
        request.setAttribute("errorMsg", "验证码已失效，请重新输入！");
        return "验证码已失效，请重新输入！";
    }else {
        session.removeAttribute("simpleCaptcha");
        return "1";
    }
}