How to Iterate over an ArrayList within a HashMap in JSTL?

Iterating an ArrayList inside a HashMap in JSTL

In Java Server Pages (JSP), the Java Standard Tag Library (JSTL) provides convenient tags for iterating over data structures. This includes iterating over maps, where each key-value pair is stored as a Map.Entry object.

To iterate over both the keys and values of a HashMap, including any ArrayLists stored as values, you can use nested tags as follows:

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

<c:forEach items="${myMap}" var="entry">
    <span>Key: ${entry.key}</span>
    
    <c:forEach items="${entry.value}" var="item" varStatus="loop">
        <span>Value: ${item}</span>
        <c:if test="${!loop.last}">, </c:if>
    </c:forEach>
    
    <br>
</c:forEach></code>

This code iterates over the myMap HashMap and, for each key-value pair, outputs the key followed by a list of values in the corresponding ArrayList. The varStatus attribute is used to determine whether the current item is the last in the list, so that a comma is added between items only if they are not the last.

Additional Notes:

• For more complex scenarios, you may need to cast the entry.key and entry.value objects to the appropriate types.
• The nested tag iterates over the ArrayList as a whole, so if you need to access individual elements within the ArrayList, you'll need to use additional logic.

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