private static final String SYMBOLS = "0123456789";
 /**
  * Math.random生成的是一般隨機(jī)數(shù)，采用的是類似于統(tǒng)計(jì)學(xué)的隨機(jī)數(shù)生成規(guī)則，其輸出結(jié)果很容易預(yù)測，因此可能導(dǎo)致被攻擊者擊中。
  * 而SecureRandom是真隨機(jī)數(shù)，采用的是類似于密碼學(xué)的隨機(jī)數(shù)生成規(guī)則，其輸出結(jié)果較難預(yù)測，若想要預(yù)防被攻擊者攻擊，最好做到使攻擊者根本無法，或不可能鑒別生成的隨機(jī)值和真正的隨機(jī)值。
  */
 private static final Random RANDOM = new SecureRandom();

 public static String generateVerCode() {
  char[] nonceChars = new char[6];
  for (int i = 0; i < nonceChars.length; i++) {
   nonceChars[i] = SYMBOLS.charAt(RANDOM.nextInt(nonceChars.length));
  }
  return new String(nonceChars);
 }

 /**
  *計(jì)算兩個日期的分鐘差
  */
 public static int getMinute(Date fromDate, Date toDate) {
  return (int) (toDate.getTime() - fromDate.getTime()) / (60 * 1000);

 /**
  * 發(fā)送驗(yàn)證碼到指定郵箱
  * @param sender 發(fā)送地址
  * @param mailSender spring自帶
  * @param receiver 接受地址
  */
 AdvanceResponse getCode(String sender,JavaMailSenderImpl mailSender,String receiver);
 /**
  * 注冊用戶
  */
 AdvanceResponse addUser(User user,String verCode);

/**
 * 驗(yàn)證碼
*/
private String code;
/**
 * 發(fā)送時間
*/
private Date sendTime;
 @Override
 @Async
 public AdvanceResponse getCode(String sender, JavaMailSenderImpl mailSender, String receiver) {
  SimpleMailMessage message = new SimpleMailMessage();
  message.setSubject("驗(yàn)證碼");//設(shè)置郵件標(biāo)題
  code = VerCodeGenerateUtil.generateVerCode();
  sendTime = new Date();
  message.setText("尊敬的用戶,您好:\n"
    + "\n本次請求的郵件驗(yàn)證碼為:" + code + ",本驗(yàn)證碼5分鐘內(nèi)有效，請及時輸入。（請勿泄露此驗(yàn)證碼）\n"
    + "\n如非本人操作，請忽略該郵件。\n(這是一封自動發(fā)送的郵件，請不要直接回復(fù)）"); //設(shè)置郵件正文
  message.setFrom(sender);//發(fā)件人
  message.setTo(receiver);//收件人
  mailSender.send(message);//發(fā)送郵件
  return AdvanceResponse.successResponse();
 }

 @Override
 public AdvanceResponse addUser(User user, String verCode) {
  Date date = new Date();
  //判斷驗(yàn)證碼
  if (VerCodeGenerateUtil.getMinute(sendTime, date) > 5) {
   return AdvanceResponse.failedResponse("驗(yàn)證碼已經(jīng)失效?。?！");
  }
  if (!verCode.equals(code)) {
   return AdvanceResponse.failedResponse("驗(yàn)證碼不正確?。?！");
  }
  user.setRole(0);
  user.setCreateTime(date);
  user.setUpdateTime(date);
  userDao.insert(user);
  code = null;
  return AdvanceResponse.successResponse();
 }

@Autowired
 private UserService userService;
 @Autowired
 private JavaMailSenderImpl mailSender;
 @Value("${spring.mail.username}")
 private String sender;
 
 /**
  * 發(fā)送驗(yàn)證碼到指定郵箱
  */
 @GetMapping("/verCode")
 public AdvanceResponse verCode(String receiver) {
  return userService.getCode(sender, mailSender, receiver);
 }

 /**
  * 注冊用戶
  */
 @PostMapping("/addUser")
 public AdvanceResponse addUser(User user, String sender, JavaMailSenderImpl mailSender, @RequestParam("verCode") String verCode) {
  return userService.addUser(user,verCode);
 }

 <div class="layui-form-item">
    <label for="email" class="layui-form-label">
     <span class="x-red">*</span>郵箱
    </label>
    <div class="layui-input-inline">
     <input type="email" id="email" name="email" required="" lay-verify="email"
       autocomplete="off" class="layui-input">
    </div>
    <div class="layui-form-mid layui-word-aux">
     <span class="x-red" id="emailMsg"></span>
    </div>
    <button type="button" class="layui-btn" id="code">獲取驗(yàn)證碼</button>
   </div>
   <div class="layui-form-item">
    <label for="verCode" class="layui-form-label">
     <span class="x-red">*</span>驗(yàn)證碼
    </label>
    <div class="layui-input-inline">
     <input type="text" id="verCode" name="verCode" required=""
       autocomplete="off" class="layui-input">
    </div>
    <div class="layui-form-mid layui-word-aux">
     <span class="x-red" id="verCodeMsg"></span>
    </div>
</div>

 //獲取驗(yàn)證碼
 $('#code').click(function () {
  const email = $('#email').val();
  const myReg = /^[a-zA-Z0-9_-]+@([a-zA-Z0-9]+\.)+(com|cn|net|org)$/;
  if (email === null || email.length === 0) {
   layer.msg('郵箱不能為空！', {time: 1500, icon: 5, shift: 6});
   return false;
  }
  if (!myReg.test(email)) {
   layer.msg('郵箱格式不正確！', {time: 1500, icon: 5, shift: 6});
   return false;
  }
  $.ajax({
   type: 'GET',
   url: 'user/verCode',
   data: {
    'receiver': email
   },
   beforeSend: function () {
    loading = layer.msg('處理中', {icon: 16})
   },
   success: function () {
    layer.close(loading);
   }
  })
 });
 //這是提交表單，只保留關(guān)鍵部分
 $.ajax({
   type: 'POST',
   url: 'user/addUser',
   data: formData,
   cache: false,   // 不緩存
   processData: false,  // jQuery不要去處理發(fā)送的數(shù)據(jù)
   contentType: false,  // jQuery不要去設(shè)置Content-Type請求頭
   beforeSend: function () {
    loading = layer.msg('處理中', {icon: 16})
   },
   success: function (result) {
    if (result.status === 0) {
     layer.msg(result.msg, {time: 1500, icon: 5, shift: 6});
    } else {
     layer.close(loading);
     xadmin.close();
    }
   }
  })