<label for="name">性別</label>
<select class="form-control" name="" id="gender" value="${Users.user_gender }">
    <option value="0">請選擇</option>
    <option value="1">男</option>
    <option value="2">女</option>
</select>

<script type="text/javascript">
 var gender = '${Users.getUser_gender()}';
 var sel = document.getElementById("gender");
 for (var i=0;i<sel.options.length;i++){
	 if (sel.options[i].value==gender){
		 sel.options[i].selected=true;
		 break;
	 }
 }
</script>