提交form表单后，先进行输入的校验。客户端（将方法写在js里面）

 jsp：
 <script type="text/javascript">
  function check(){
   var userName = document.getElementById("name").value;
   var pass1 = document.getElementById("pass1").value;
   var pass2 = document.getElementById("pass2").value;
   var email = document.getElementById("email").value;  
   if(userName == ""|| pass1 == ""|| pass2 == ""|| email == ""){
    alert("请将登录信息填写完整");
    return false;
   }
  }
 </script>



  <form action="#" method="post" onsubmit="return check();" />
  <input type="text" name="user.name" id="pass1" />
  <input type="password" name="user.pass" id="pass2" />
  <input type="password" id="name">
  <input type="text" name="user.email" id="email" />
  <input type="reset" value="重置" />
  <input type="submit" value="注册" />
  </form>

    if(userName.length<15||userName.length>3){  
     pName.innerHTML = "";
     return false;
    }

看demo：