生成验证码

@RequestMapping(value = "/getVerify")
 public void getVerify(HttpServletRequest request, HttpServletResponse response ) {
     //设置相应类型,告诉浏览器输出的内容为图片
     response.setContentType("image/jpeg");
     //设置响应头信息，告诉浏览器不要缓存此内容
     response.setHeader("Pragma", "No-cache");
     response.setHeader("Cache-Control", "no-cache");
     response.setDateHeader("Expire", 0);
     Verify randomValidateCode = new Verify();
     try {
         //输出验证码图片方法
         randomValidateCode.getRandcode(request, response);
     } catch (Exception e) {
         e.printStackTrace();
     }
 }

 //放到session中的key
 public static final String RANDOMCODEKEY= "RANDOMVALIDATECODEKEY";
 //随机产生数字与字母组合的字符串
 private String randString = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 // 图片宽
 private int width = 95;
 // 图片高
 private int height = 25;
 // 干扰线数量
 private int lineSize = 40;
 // 随机产生字符数量
 private int stringNum = 4;

 private Random random = new Random();

 //获得字体
 private Font getFont() {
     return new Font("Fixedsys", Font.CENTER_BASELINE, 18);
 }

 // 获得颜色
 private Color getRandColor(int fc, int bc) {
     if (fc > 255)
         fc = 255;
     if (bc > 255)
         bc = 255;
     int r = fc + random.nextInt(bc - fc - 16);
     int g = fc + random.nextInt(bc - fc - 14);
     int b = fc + random.nextInt(bc - fc - 18);
     return new Color(r, g, b);
 }

 /**
  * 生成随机图片
  */
 public void getRandcode(HttpServletRequest request, HttpServletResponse response) {
     HttpSession session = request.getSession();
     // BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类
     BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
     // // 产生Image对象的Graphics对象,改对象可以在图像上进行各种绘制操作
     Graphics g = image.getGraphics();
     g.fillRect(0, 0, width, height);
     g.setFont(new Font("Times New Roman", Font.ROMAN_BASELINE, 18));
     g.setColor(getRandColor(110, 133));
     // 绘制干扰线
     for (int i = 0; i <= lineSize; i++) {
         drowLine(g);
     }
     // 绘制随机字符
     String randomString = "";
     for (int i = 1; i <= stringNum; i++) {
         randomString = drowString(g, randomString, i);
     }

     //将生成的随机字符串保存到session中，而jsp界面通过session.getAttribute("RANDOMCODEKEY")，
     //获得生成的验证码，然后跟用户输入的进行比较
     session.removeAttribute(RANDOMCODEKEY);
     session.setAttribute(RANDOMCODEKEY, randomString);
     g.dispose();
     try {
         // 将内存中的图片通过流动形式输出到客户端
         ImageIO.write(image, "JPEG", response.getOutputStream());
     } catch (Exception e) {
         e.printStackTrace();
     }
 }

// 绘制字符串
 private String drowString(Graphics g, String randomString, int i) {
     g.setFont(getFont());
     g.setColor(new Color(random.nextInt(101), random.nextInt(111), random
             .nextInt(121)));
     String rand = String.valueOf(getRandomString(random.nextInt(randString
             .length())));
     randomString += rand;
     g.translate(random.nextInt(3), random.nextInt(3));
     g.drawString(rand, 13 * i, 16);
     return randomString;
 }

 // 绘制干扰线
 private void drowLine(Graphics g) {
     int x = random.nextInt(width);
     int y = random.nextInt(height);
     int xl = random.nextInt(13);
     int yl = random.nextInt(15);
     g.drawLine(x, y, x + xl, y + yl);
 }

 // 获取随机的字符
 public String getRandomString(int num) {
     return String.valueOf(randString.charAt(num));
 }

// 因为现在大部分业务都不用jsp页面所有我们在开发中 校验验证码在后台校验即可 

前台js

<div class="form-group has-feedback">
    <input type="text" name="verification" id="verification" class="form-control" placeholder="请输入验证码">
    <img id="imgVerify"  src="" onclick="getVerify();" alt="点击更换验证码"/>
     <a href="#" onclick="getVerify();" rel="nofollow">看不清? 换一张</a>
</div>

$(document.body).ready(function () {
    // 设置a标签字体大小
    $("a").css('font-size','10px')
   //首次获取验证码
    $("#imgVerify").attr("src", "/getVerify/getVerify?" + Math.random());
})
// 重新获取验证码
function getVerify() {
    var src1 = document.getElementById('imgVerify')
    src1.src = "/getVerify/getVerify?" + Math.random();
}
// 获取到输入的值

var verify = $("#verification").val();

// 获取到session
HttpSession session = request.getSession();
// 获取到生成的验证码的值
Object randomvalidatecodekey = session.getAttribute("RANDOMVALIDATECODEKEY");