如何在 <c:forEach> 中迭代嵌套映射 [英] How to iterate over a nested map in <c:forEach>

问题描述

我在 bean 中有一个 Map 如下:

I've a Map in a bean as follows:

public class TaskListData {
    private Map<String, String[]> srcMasks = new HashMap<String, String[]>();
    private Map<Integer, Map<String, String[]>> ftqSet = new HashMap<Integer, Map<String, String[]>>();

    public void setFTQSet(Integer ftqid, String[] src, String[] masks) {  
        srcMasks.put("srcDir", src);
        srcMasks.put("masks", masks);
        ftqSet.put(ftqid, srcMasks);
    }

这个ftqSet适合以下数据结构:

This ftqSet fits in below datastructure:

feedId = "5",
feedName = "myFeedName",
ftqSet => {
            1 => {
                    srcDirs = ["/path/string"],
                    masks = ["p.txt", "q.csv"]
                 }
            2 => { ...
                 }
          }, ...

在我的测试 JSP 文件中，我一直在尝试使用 <c:forEach>:

In my test JSP file I've been trying to access the data using <c:forEach>:

<c:forEach items="#{bean.ftqSet}" var="f">
    this text does not print
    ${f.feedId}
</c:forEach>

但它没有输出 ${f.feedId}.为什么会这样?我将如何访问此结构的各个元素，以便创建一个漂亮的表格?

But it's not outputting ${f.feedId}. Why would this be? How would I access this structure's individual elements so I can create a nice table?

推荐答案

c:forEach 中 Map 的每次迭代都会给出一个 Map.Entry 实例，该实例又具有getKey() 和 getValue() 方法.这类似于在普通 Java 中执行 for (Entry entry : map.entrySet()).

Each iteration of Map in a c:forEach gives a Map.Entry instance which in turn has getKey() and getValue() methods. It's similar to doing for (Entry entry : map.entrySet()) in plain Java.

例如

<c:forEach items="#{bean.map}" var="entry">
    <h:outputText value="Key: #{entry.key}, Value: #{entry.value}" /><br />
</c:forEach>

在 Map> 的情况下，#{entry.value} 返回一个 Map，所以你也需要遍历它:

In case of a Map<Integer, Map<String, String[]>> the #{entry.value} returns a Map<String, String[]>, so you need to iterate over it as well:

<c:forEach items="#{bean.map}" var="entry">
    <h:outputText value="Key: #{entry.key}, Values:" />
    <c:forEach items="#{entry.value}" var="nestedentry">
        <h:outputText value="Nested Key: #{nestedentry.key}, Nested Value: #{nestedentry.value}" />
    </c:forEach><br />
</c:forEach>

但在你的情况下，#{nestedentry.value} 实际上是一个 String[]，所以我们需要再次迭代它:

But in your case, the #{nestedentry.value} is actually a String[], so we need to iterate over it again:

<c:forEach items="#{bean.map}" var="entry">
    <h:outputText value="Key: #{entry.key}, Values:" />
    <c:forEach items="#{entry.value}" var="nestedentry">
        <h:outputText value="Nested Key: #{nestedentry.key}, Nested Values: " />
        <c:forEach items="#{nestedentry.value}" var="nestednestedentry">
            <h:outputText value="#{nestednestedentry}" />
        </c:forEach><br />
    </c:forEach><br />
</c:forEach>

顺便说一下，这应该也适用于 rich:dataList.

By the way, this ought to work with rich:dataList as well.

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