file控件禁止手寫，是否爲空驗證，文件類型驗證，file控件清空。
<html>
<body bgcolor="white">
<TABLE cellSpacing=0 cellPadding=0 width="100%" border=0>
<TBODY>
<TR>
<TD>
<center>
<h4>
考勤記錄導入
</h4>
</center>
<hr/>
<br/>
<center>
<form action="<%=request.getContextPath() %>/admin/HtmlFile.do" method="post" enctype="multipart/form-data" name="HtmlFileForm" οnsubmit="return check()">
<span id='uploadSpan'>
<input type="file" name="file" id="file" unselectable="on" οnchange='checkFileType(this.value);'/>
</span>
<input type="submit" value="提交"/>
</form>
</center>
</TD>
</TR>
</TBODY>
</TABLE>
<script type="text/javascript">
function checkFileType(str){
var pos = str.lastIndexOf(".");
var lastname = str.substring(pos,str.length);
var resultName=lastname.toLowerCase();
if ('.xls'!=resultName.toString()){alert('只能上傳xls文件，您上傳的文件類型爲'+lastname+'，請重新上傳');
resetFile();
}
}
var html=document.getElementById('uploadSpan').innerHTML;
function resetFile(){
document.getElementById('uploadSpan').innerHTML=html;
}
function check()
{
if(HtmlFileForm.file.value == "") {
alert("請選擇文件路徑");
return false;
}else{
return true;
}
}
</script>
</body>
</html>