在html文档的
</body>
标签前加入以下代码即可实现：
<script type="text/javascript">
$(document).ready(function(){
$(".dropdown").mouseover(function(){
$(this).addClass("open");
});
$(".dropdown").mouseleave(function(){
$(this).removeClass("open");
});
});
</script>
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<title>TITLE</title>
<meta name="description" content="description" />
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<!-- 最新 Bootstrap 核心 CSS 文件 -->
<link rel="stylesheet" href="/static/bootstrap/3.0.3/css/bootstrap.min.css">
<!-- HTML5 Shim and Respond.js IE8 support of HTML5 elements and media queries -->
<!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
<!--[if lt IE 9]>
<script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>
<script src="https://oss.maxcdn.com/libs/respond.js/1.4.2/respond.min.js"></script>
<![endif]-->
</head>
<body>
<!-- jQuery (necessary for Bootstrap's JavaScript plugins) -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
<script type="text/javascript" src="//netdna.bootstrapcdn.com/bootstrap/3.0.3/js/bootstrap.min.js"></script>
</body>
</html>