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    1.当输入用户名和密码为空的时候,需要判断。这时候就用到了校验用户名和密码,这个需要在jsp的前端页面写;有两种方法,一种是用submit提交。一种是用button提交。
    方法一:

    在jsp的前端页面的头部插入一个js方法:

     function checkUser(){
       var result = document.getElementById("userid").value;
       var password = document.getElementById("userpassid").value;
       if(result == ""  ){
         alert("用户名不能为空");
         return false;
       }
       if(password == ""  ){
        alert("密码不能为空");
         return false;
       }else{
       return true;
       }
    }

    在form表单里写成这样:

    <form id="formid"  name= "myform" method = 'post'  action = 'user_login_submit.action' onsubmit = "return checkUser();" >
                <table width="100%" border="0">
                  <tr>
                    <td width="60" height="40" align="right">用户名&nbsp;</td>
                    <td><input type="text" value="" class="text2" name = "username" id = "userid"/></td>
                  </tr>
                  <tr>
                    <td width="60" height="40" align="right">密&nbsp;&nbsp;码&nbsp;</td>
                    <td><input type="password" value="" class="text2" name = "userpass" id = "userpassid"/></td>
                  </tr>
                  <tr>
                    <td width="60" height="40" align="right">&nbsp;</td>
                    <td><div class="c4">
                        <input type="submit" value="" class="btn2"  />

     

    方法二:

    function checkUser(){
       var result = document.getElementById("userid").value;
       var password = document.getElementById("passid").value;

       if(result == ""  ){
         alert("用户名不能为空");
         return false;
       }
       if(password == ""  ){
        alert("密码不能为空");
         return false;
       }
      document.getElementById("formid").submit();
    }

    form表格的写法,需要写id
     <form id="formid" method = 'post'  action = 'user_login_submit.action'  >

    button按钮的写法如下:

    <input type="button" value="" class="btn2" onclick = "checkUser();" />

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  • 原文地址:https://www.cnblogs.com/blogofwyl/p/4274833.html
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