Question

I want to do the below thing in JSP starting from for loop– I just want to loop HashSet and HashMap and print the result

private static HashMap<Long, Long> histogram = new HashMap<Long, Long>();
private static Set<Long> keys = histogram.keySet();

for (Long key : keys) {
    Long value = histogram.get(key);
    System.out.println("MEASUREMENT, HG data, " + key + ":" + value);
}

I am working with Spring MVC, so I added these two things in my model

model.addAttribute("hashSet", (keys));
model.addAttribute("histogram", (histogram));

And in my JSP page, I was doing something like this to emulate the above JAVA code but it was giving me an exception that something is wrong in my JSP page.

<fieldset>
    <legend>Performance Testing:</legend>
        <pre>

            <c:forEach items="${hashSet}" var="entry">
            Key = ${entry.key}, value = ${histogram}.get(${entry.key})<br>
            </c:forEach>


        </pre>
        <br />
</fieldset>

Exception I got-

Caused by: javax.el.PropertyNotFoundException: Property 'key' not found on type java.lang.Long
    at javax.el.BeanELResolver$BeanProperties.get(BeanELResolver.java:195)
    at javax.el.BeanELResolver$BeanProperties.access$400(BeanELResolver.java:172)
    at javax.el.BeanELResolver.property(BeanELResolver.java:281)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:62)

Can anyone help me out with this?

Answer 1

You don’t need to make use of keySet to access the values in the HashMap. When you iterate over HashMap using <c:forEach..>, you get back the EntrySet, for which you can use: – EntrySet#getKey() and EntrySet#getValue() directly: –

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