Question

I was wondering if there is a way to register default renderer for a particular class in JSP/JSTL.

I am on my page displaying a tabular report where each table row arrives as generic List<Object>. Since I don’t know the type of particular item in advance I am outputting the value with <c:out ...>. This does toString() as far as I know.

Now I want to change the format based on the class of the item e.g. change the format of decimal numbers. Of course I can’t use <fmt:formatXXX ...> because I don’t know the type in advance.

I believe this is possible in JSF. But is there a way how to achieve this in JSP?

My best shot sofar would be to convert the List<Object> to List<String> and applying the formatting in my controller class but this is slightly less elegant than register a renederer IMHO.

Answer 1

JSP has no notion of “renderers”, it’s not a component based MVC framework. But you could create a custom tag for this.

Alternatively, you can do something like this with plain JSTL, it’s possible to figure the class of an EL object by just checking Object#getClass():

<c:choose>
    <c:when test="${item['class'].name == 'java.lang.Integer'}">
        <fmt:formatNumber value="${item}" type="number" />
    </c:when>
    <c:when test="${item['class'].name == 'java.math.BigDecimal'}">
        <fmt:formatNumber value="${item}" type="currency" />
    </c:when>
    <c:when test="${item['class'].name == 'java.util.Date'}">
        <fmt:formatDate value="${item}" type="date" />
    </c:when>
    <c:otherwise>
        <c:out value="${item}" />
    </c:otherwise>
</c:choose>