<s:form method="post" action="updatePortal" enctype ="multipart/form-data" onsubmit="return checkImg();">

上传新图片:<s:file name="myFile" label="Image File" id="uploadImg"></s:file>

<s:submit value="提 交"/>
</s:form>


<script type="text/javascript">
	function checkImg()
	{
		var str=document.getElementById("uploadImg").value;
		if(!str.equals(''))
		{
			if(str.substring((str.lastIndexOf(".jpg")))==(".jpg"))
	 		{
	 			
	 		}else
	 		{
	 			alert('只允许jpg格式图片!');
	 			return false;
	 		}
		}
 		
		
	}
</script>