How to Iterate over ArrayLists in HashMaps using JSTL?

Iterating ArrayLists within HashMaps using JSTL

Question:

Iterating over a HashMap itself is straightforward using JSTL's tag. However, how do you iterate over the ArrayList values associated with each key in the HashMap?

Solution:

JSTL's tag provides flexibility in iterating over different data structures, including maps.

Iterating the Map:

<code class="jsp"><%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<c:forEach items="${myMap}" var="entry"></code>

This iterates over the map's entries, where each entry is a Map.Entry object with getKey() and getValue() methods.

Iterating the ArrayList:

To access the ArrayList associated with an entry, use entry.getValue(), which returns the list as an object. You can then iterate over the list as follows:

<code class="jsp"><c:forEach items="${entry.value}" var="item"></code>

Combined Example:

<code class="jsp"><c:forEach items="${myMap}" var="entry">
    Key: ${entry.key}<br>
    Values:<br>
    <c:forEach items="${entry.value}" var="item">
        ${item}
        ${!loop.last ? ', ' : ''}
    </c:forEach><br>
</c:forEach></code>

This example iterates over the map, retrieving the ArrayList associated with each key. It then iterates over the ArrayList, displaying the key and values.

Additional Notes:

• The varStatus object provides additional information during the iteration, such as the current index.
• For a better understanding, refer to the provided Java translation of the JSTL code.

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