从基于JSTL密钥的hashmap获取值 [英] Get value from hashmap based on key to JSTL

问题描述

我想根据键获取 HashMap 的值。

I want to get the value of HashMap based on key.

HashMap<String, ArrayList<String>> map 
    = new HashMap<String, ArrayList<String>>();
ArrayList<String> arrayList = new ArrayList<String>();

map.put("key", arrayList);
request.setAttribute("key", map);

我做的是

What i did is

<c:forEach var="map" items="${requestScope.key}">
    <c:forEach var="hash" items="${map.value}">
        <option><c:out value="${hash}"/></option>
    </c:forEach>
</c:forEach>

但是它似乎在打印所有内容，我想要做的是获取值取决于键： hash.key 或其他

But it seems it's printing everything, what i want to do is to get the value depends on key like: hash.key or something

更新：

我做了这样的事情，但它仍然无法工作

UPDATE:
I did something like this but it still doesn't work

<c:forEach var="map" items="${requestScope.key}">
    <c:forEach var="hash" items="${map['key']}">
        <option><c:out value="${hash}"/></option>
    </c:forEach>
</c:forEach>

和StackTrace：在类型java.util中找不到Property'External' .HashMap $ Entry

我很确定这里有那种键。

and the StackTrace: Property 'External' not found on type java.util.HashMap$Entry
I'm pretty sure that there is really that kind of key.

推荐答案

如果你所要做的只是获取地图中单个条目的值，那么根本就不需要循环任何集合。轻微简化gautum的响应，你可以得到一个有名的map条目的值如下：

if all you're trying to do is get the value of a single entry in a map, there's no need to loop over any collection at all. simplifying gautum's response slightly, you can get the value of a named map entry as follows:

<c:out value="${map['key']}"/>

其中'map'是集合，'key'是您正在尝试的字符串键提取值。

where 'map' is the collection and 'key' is the string key for which you're trying to extract the value.

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