How do I round a number in JSTL?

Question

Hi,

I'm doing a division in a JSP and I'd like to round the result - how should I do this?

i.e.

<c:set
  var="expiry"
  value="${(expire.time - now.time) / (60 * 1000)}"/>

...how do I round the result?

Thanks,

Answer 1

What about this dirty hack:

<c:set
  var="expiry"
  value="${(((expire.time - now.time) / (60 * 1000) * 100) - 0.5) / 100.0}"/>

But I would do this in a bean and just show the result here. Beside this, you can define functions in your tld or, if that is not supported in your environment get functions in the expression language by implementing a Map and (ab)use it. You implement the get(Object) method to do what you want and call it like this:

<c:set
  var="expiry"
  value="${Helpers.round[(expire.time - now.time) / (60 * 1000)]"/>

Note, Helpers provides a "getRound()" method which returns your Map implementation.

Answer 2

It may looks like:

<c:set var="expire" value="100"/>
<c:set var="now" value="3"/>

<c:choose>
 <c:when test="${(expire mod now)!=0}">
  <c:set var="res" value="${(expire - (expire mod now))/now}"/>
  ${res}
 </c:when>
 <c:otherwise>
  <c:set var="res" value="${expire/now}"/>
  ${res}
 </c:otherwise>
</c:choose>

note: i think you should use mod anyway or % functionality of jstl,i use mod in example. Test,please, "expire" and "now" variables with different values, should work ok.

Answer 3

Actually in this case, it is fine to truncate the fractional component instead of properly rounding it, so I am going to use:

<fmt:formatNumber var="expiry"
  value="${(expire.time - now.time) / (60 * 1000)}"
  pattern="0"/>

The other answers give options for properly rounding the number.

Answer 4

I used:

${fn:substringBefore(expiry, '.')}

which truncates rather than rounding, but that may be good enough.