function checkUsername(){
 var username = $("#username").val();
 $("#span1").load("${pageContext.request.contextPath}/user_checkUsername.action",{'username':username});
}　

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE validators PUBLIC
  "-//Apache Struts//XWork Validator 1.0.3//EN"
  "http://struts.apache.org/dtds/xwork-validator-1.0.3.dtd">
<validators>
 <!-- name:要校驗的字段名 -->
 <field name="username">
 <field-validator type="requiredstring">
  <message>用戶名不能為空!</message>
 </field-validator>
 </field>
 
 <!-- name:要校驗的字段名 -->
 <field name="password">
 <field-validator type="requiredstring">
  <message>密碼不能為空!</message>
 </field-validator>
 </field>
 
 
 <!-- 校驗郵箱 -->
 <field name="email">
 <field-validator type="email">
  <message>郵箱格式不正確!</message>
 </field-validator>
 </field>
 
 <!-- 校驗電話 -->
 <field name="phone">
 <field-validator type="regex">
  <param name="regex"><![CDATA[^15\d{9}$]]></param>
  <message>電話不合法</message>
 </field-validator>
 </field>
</validators>

/**
 * 注冊用戶的方法
 * @param user
 */
public void save(User user) {
 // 保存到數(shù)據(jù)庫:
 user.setState(0); // 0:未激活 1:已經(jīng)激活
 String code = UUIDUtils.getUUID()+UUIDUtils.getUUID();
 user.setCode(code);
 userDao.save(user);
 // 發(fā)送一封激活郵件:
 MailUtils.sendMail(user.getEmail(), code);
}

/**
 * 發(fā)送郵件方法:
 */
public static void sendMail(String to,String code){
 Properties props = new Properties();
 props.setProperty("mail.smtp", "localhost");
 // 1.獲得連接:
 Session session = Session.getInstance(props, new Authenticator() {
 
 @Override
 protected PasswordAuthentication getPasswordAuthentication() {
  return new PasswordAuthentication("service@shop.com", "111");
 }
  
 });
 // 2.創(chuàng)建一個郵件的對象
 Message message = new MimeMessage(session);
 // 設(shè)置發(fā)件人:
 try {
 message.setFrom(new InternetAddress("service@shop.com"));
 // 設(shè)置收件人:
 message.setRecipient(RecipientType.TO, new InternetAddress(to));
 // 設(shè)置主題:
 message.setSubject("來自ITCASTSHOP商城激活郵件");
 // 設(shè)置郵件正文:
 message.setContent("<h1>來自ITCASTSHOP購物天堂的激活郵件</h1><h3><a text/html;charset=UTF-8");
 // 發(fā)送郵件:
 Transport.send(message);
 } catch (AddressException e) {
 e.printStackTrace();
 } catch (MessagingException e) {
 e.printStackTrace();
 }
}

/**
 * 用戶激活的方法:
 */
public String active() {
 // 模型驅(qū)動會接收激活碼:
 // 按照激活碼查詢用戶 :
 User existUser = userService.findByCode(user.getCode());
 if (existUser == null) {
 // 激活碼篡改
 this.addActionMessage("激活失敗:激活碼被篡改了!");
 } else {
 // 激活:修改用戶狀態(tài)
 existUser.setState(1);
 userService.update(existUser);
 // 激活成功:
 this.addActionMessage("激活成功:請去登錄!");
 }
 return "msg";
}