How to Iterate an ArrayList Inside a HashMap Using JSTL?

Iterating an ArrayList Inside a HashMap Using JSTL

In web development, JSTL (JavaServer Pages Standard Tag Library) provides a set of tags for simplifying common tasks in JSP (JavaServer Pages). One such task is iterating over data structures.

To iterate over a HashMap and the ArrayLists contained within it, you can use JSTL's tag. It enables looping through collections and maps:

For arrays and collections, var gives you the currently iterated item.

<code class="html"><c:forEach items="${collectionOrArray}" var="item">
    Item = ${item}<br>
</c:forEach></code>

For maps, var gives you a Map.Entry object, which has getKey() and getValue() methods.

<code class="html"><c:forEach items="${map}" var="entry">
    Key = ${entry.key}, value = ${entry.value}<br>
</c:forEach></code>

Since the entry.value is a list, iterate over it as well:

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

The varStatus attribute enhances readability by tracking the loop's iteration status.

A similar Java implementation below helps understand the process:

<code class="java">for (Entry<String, List<Object>> entry : map.entrySet()) {
    out.print("Key = " + entry.getKey() + ", values = ");
    for (Iterator<Object> iter = entry.getValue().iterator(); iter.hasNext();) {
        Object item = iter.next();
        out.print(item + (iter.hasNext() ? ", " : ""));
    }
    out.println();
}</code>

For further reference, review the following resources:

• [Looping through HashMap in JSP](https://stackoverflow.com/questions/11085751/how-to-loop-through-a-hashmap-in-jsp)
• [Displaying JDBC ResultSet in JSP using MVC and DAO](https://stackoverflow.com/questions/23612802/show-jdbc-resultset-in-html-in-jsp-page-using-mvc-and-dao-pattern)
• [Looping a specified number of times in JSTL](https://stackoverflow.com/questions/1054242/how-to-loop-over-something-a-specified-number-of-times-in-jstl)

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