How to Loop Through a HashMap in JSP Using <c:forEach>

How can I use <c:forEach> to iterate over a HashMap in a JSP page?

<c:forEach var="entry" items="${types.entrySet()}">
    <c:set var="key" value="${entry.key}" />
    <c:set var="value" value="${entry.value}" />
    <!-- Process the key and value here -->
</c:forEach>

You can effectively utilize the <c:forEach> tag from JSTL to loop through a HashMap in your JSP by casting the HashMap to a collection that <c:forEach> can iterate over. Below are the detailed steps and an example of how to achieve this.

<c:forEach var="entry" items="${types.entrySet()}">
    <c:set var="key" value="${entry.key}" />
    <c:set var="value" value="${entry.value}" />
    <!-- Example of outputting key-value pairs -->
    Key: ${key}, Value: ${value}<br/>
</c:forEach>

Causes

• The <c:forEach> tag cannot directly iterate over a HashMap as it expects a collection.
• JSTL does not provide direct support for HashMap, but you can convert it to a Set or List.

Solutions

• Use the entrySet() method of the HashMap to create a Set of Map.Entry objects that can be iterated with <c:forEach>.
• Alternatively, convert the HashMap entries to a List if specific ordering or additional processing is necessary.

Mistake: Trying to iterate directly over the HashMap without converting it to a Set or List.

Solution: Always use <c:forEach> with ${yourMap.entrySet()} to get a collection compatible with the tag.

Mistake: Using incorrect variable names in JSTL expressions.

Solution: Ensure variable names in JSTL match those set in your Servlet.