根据hashmaps列表动态生成h：列 [英] Dynamically generate h:column based on list of hashmaps

问题描述

在我的应用程序中，我想使用托管bean属性显示一个< h：dataTable> 。目前，此表是从列表< Folder> 创建的。现在我想将文件夹更改为更动态的东西。这是因为如果我稍后决定添加另一个字段，我不想更改文件夹类。我只需要在 Map< String，Object> 中添加另一个条目，而不是在文件夹中引入一个新的字段。

In my application I want to display a <h:dataTable> with managed bean properties. Currently this table is created from a List<Folder>. Now I want to change the Folder to something more dynamic. That's because I don't want to change the Folder class if I decide to add another field later. I would just have to add another entry in the Map<String, Object> instead of introducing a new field in Folder.

所以，是否可以将 List< Map< String，Object>> c $ c>< h：dataTable> ？

So, is it possible to bind a List<Map<String, Object>> to the <h:dataTable>?

推荐答案

可以将HashMaps列表绑定到jsf组件h：dataTable？

如果您使用视图构建时间标签（如JSTL < c：forEach> < h：column> $ c>。

That's only possible if you generate the necessary <h:column> tags with a view build time tag such as JSTL <c:forEach>.

这是一个具体的开始示例，假设您的环境支持EL 2.2：

Here's a concrete kickoff example, assuming that your environment supports EL 2.2:

<h:dataTable value="#{bean.listOfMaps}" var="map">
    <c:forEach items="#{bean.listOfMaps[0].keySet().toArray()}" var="key">
        <h:column>
            #{map[key]}
        </h:column> 
    </c:forEach>
</h:dataTable>

（如果您的环境不支持EL 2.2，您需要提供另一个getter返回映射密钥设置为 String [] 或 List< String> ;还要记住 HashMap 本质上是无序的，您可能需要使用 LinkedHashMap 来维护插入顺序）

(if your environment doesn't support EL 2.2, you'd need to provide another getter which returns the map key set as a String[] or List<String>; also keep in mind that a HashMap is by nature unordered, you might want to use LinkedHashMap instead to maintain insertion order)

当您使用早于2.1.18的Mojarra版本时，缺点是＃{bean} 必须请求范围（不是查看范围）。或至少，< c：forEach items> 应该引用一个请求作用域bean。否则，在视图构建时间期间，当视图范围不可用时，视图范围bean将在每个单个HTTP请求上重新创建，因为< c：forEach> 运行。如果您绝对需要< h：dataTable> 的视图范围bean，那么您可以随时创建一个单独的请求作用域bean，用于 c：forEach items> 。解决方案是升级到Mojarra 2.1.18或更新版本。有关一些背景信息，另请参阅 JSF2 Facelets中的JSTL有意义？

When you're using Mojarra version older than 2.1.18, the disadvantage is that the #{bean} has to be request scoped (not view scoped). Or at least, the <c:forEach items> should refer a request scoped bean. A view scoped bean would otherwise be recreated on every single HTTP request as the <c:forEach> runs during view build time, when the view scope isn't availabe yet. If you absolutely need a view scoped bean for the <h:dataTable>, then you can always create a separate request scoped bean exclusively for <c:forEach items>. The solution would be to upgrade to Mojarra 2.1.18 or newer. For some background information, see also JSTL in JSF2 Facelets... makes sense?

JSF组件库（例如 PrimeFaces ）可能会提供一个< x：columns> 标签，这使得这更容易，例如 < p：dataTable> with < p：columns> a>。

JSF component libraries such as PrimeFaces may offer a <x:columns> tag which makes this more easy, such as <p:dataTable> with <p:columns>.

<p:dataTable value="#{bean.listOfMaps}" var="map">
    <p:columns value="#{bean.listOfMaps[0].keySet().toArray()}" var="key">
        #{map[key]}
    </p:columns>
</p:dataTable>

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