Html 使用请求参数在下拉列表中选择一个选项
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selecting an option in a dropdown list using request parameters
提问by DaTaBomB
I'm kind of new to this so please bear with me. I have a value from the db which needs to set the currently selected value in a dropdown .this is passed to the front end as a request parameter. I tried using selected="parameter" attribute with the select tag but doesnt seem to work. I also tried value="", no result. Any help is appreciated. Thanks
我对此很陌生，所以请耐心等待。我有一个来自数据库的值，它需要在下拉列表中设置当前选定的值。这作为请求参数传递给前端。我尝试将 selected="parameter" 属性与 select 标记一起使用，但似乎不起作用。我也试过 value=""，没有结果。任何帮助表示赞赏。谢谢
回答by Xavi López
If you want to serve the jsp with a selected value in the <select>, put the selectedattribute in the corresponding option.
如果要服务于JSP与在选择的值<select>，把selected属性的相应option。
<select id="dropdown">
<option value="1">option 1</option>
<option value="2" selected>option 2</option>
<option value="3">option 3</option>
</select>
Use the JSTL tag <c:if>to test for equality between the request parameter and the current value. For instance, with a request parameter named selectValue:
使用 JSTL 标记<c:if>来测试请求参数和当前值之间的相等性。例如，使用名为 的请求参数selectValue：
<option
<c:if test='${param.selectValue == currentOption}'> selected </c:if>
>
</option
Take a look at the following question for details: Selected item populating in Select tag using JSTL?
有关详细信息，请查看以下问题：使用 JSTL 在 Select 标记中填充所选项目？
To elaborate on the matter, in case you're building your options dinamically (<c:forEach>), while looping the options, output selectedin the <option>when the current <option>'s value is equal to the request parameter (code untested):
为了阐述这个问题，如果你dinamically（构建选项<c:forEach>），而循环播放的选项，输出selected在<option>当电流<option>的值等于请求参数（未测试的代码）：
<select id="dropdown">
<c:forEach var="item" items="${list}">
<option value="<c:out value='${item}' />"
<c:if test="${param.selectValue == item})"> selected </c:if> >
<c:out value="${item}" />
</option>
</c:forEach>
</select>
In case the options are static, you could add something like this in each <option>(code untested):
如果选项是静态的，您可以在每个选项中添加如下内容<option>（代码未经测试）：
<option value="1"
<c:if test="${param.selectValue == 1})"> selected </c:if> >
option 1
</option>
<option value="2"
<c:if test="${param.selectValue == 2})"> selected </c:if> >
option 2
</option>
If you want to set the selected value through javascript, use for instance
如果要通过javascript设置选定的值，例如使用
document.getElementById("dropdown").value = <c:out value='${param.selectValue}'/>
回答by BalusC
To the point, you need to set the selectedattribute onlywhenever the submitted value matches the selected value. Cleanest would be to use the conditional operator ?:in EL for this as using JSTL <c:if>would end up in clumsy and hard-to-read code.
为了这一点，你需要设置selected属性只有每当提交值的选定值相匹配。最干净的方法是?:在 EL 中使用条件运算符，因为使用 JSTL<c:if>会导致代码笨拙且难以阅读。
Here's an example:
下面是一个例子：
<select name="foo">
<option value="1" ${param.foo == '1' ? 'selected' : ''}>One</option>
<option value="2" ${param.foo == '2' ? 'selected' : ''}>Two</option>
<option value="3" ${param.foo == '3' ? 'selected' : ''}>Three</option>
</select>
Please note that the fooin ${param.foo}must exactly match name of <select name="foo">. Please also note that the ${param.foo}value must exactly match the value of <option value>. The usage of idas suggested in other answer is irrelevant here. It's only relevant for the client side. IDs aren't used as request parameter names or values at all.
请注意fooin${param.foo}必须与 的名称完全匹配 <select name="foo">。另请注意，该${param.foo}值必须与 的值完全匹配<option value>。id其他答案中建议的使用在这里无关紧要。它只与客户端相关。ID 根本不用作请求参数名称或值。
回答by Ralph
You can solve this with javascript and jquery. After the page was rendered you simply update the select box and set the value provided in a param. See the following jsp/jquery example:
你可以用 javascript 和 jquery 来解决这个问题。页面呈现后，您只需更新选择框并设置参数中提供的值。请参阅以下 jsp/jquery 示例：
<select id="dropdown">
<option value="1">option 1</option>
<option value="2">option 2</option>
<option value="3">option 3</option>
</select>
<script type="text/javascript">
$(document).ready(function() {
// set select options with jquery and EL
$("#dropdown").val("${param.foo}");
});
</script>
In a JSF/Facelets page you can use this EL syntax (replace ${} with #{})
在 JSF/Facelets 页面中，您可以使用此 EL 语法（将 ${} 替换为 #{}）
$("#dropdown").val("#{param.foo}");
