How to get a random number in JSTL?

Question

I would like to get something like the next code generated in JSTL

<c:choose>
    <c:when test="${random number is even}">
        <div class="redlogo">
    </c:when>
    <c:otherwise>
        <div class="greenlogo">
    </c:otherwise>
</c:choose>

Painkiller

Answer 1

This one is a bit ugly but it works...

<c:set var="rand"><%= java.lang.Math.round(java.lang.Math.random() * 2) %></c:set>

Later you can check for ${rand mod 2 == 0} and ${rand mod 2 == 1} to get your desired output.

Eriha

Answer 2

You could wrap java.util.Random in a bean and make use of jsp:useBean.

package com.example;

import java.util.Random;

public class RandomBean {
    private static final Random RANDOM = new Random();

    public int getNextInt() {
        return RANDOM.nextInt();
    }
}

...so that you can use it in your JSP as follows:

<jsp:useBean id="random" class="com.example.RandomBean" scope="application" />

...

<div class="${random.nextInt % 2 == 0 ? 'redlogo' : 'greenlogo'}">

(note that I optimized the c:choose away with help of the ternary operator).

Mt

If there's always going to be just two values, I'd go for a nextBoolean ;) – Waterage

just a note - if EL supports calling methods, then you can skip the bean and use ${random.nextInt() ... } (+1 was given long ago :) ) – Split

@Split try you can understand. It need getter and setter – Loki

Answer 3

I just want to point out, that if you are using EL 2.2 (or above), you can directly call any method in EL (see this question), so probably the quickest method is to initialize a bean

<jsp:useBean id="random" class="java.util.Random" scope="application" />

and then directly invoke nextInt() or any other method from java.util.Random inside page:

${random.nextInt()}

or with parameter:

${random.nextInt(10)}

Alphabetical

EL would presume that java.util.Random has a method getNextInt(). Which it hasn't. – Carthy

no, it wouldn't, because you will invoke it with brackets or with arguments in brackets. Read Invoking non-getter methods section in EL wiki page – Alphabetical

I know some time has passed, but this is a far better solution than the selected answer. – Jesse

Answer 4

Hope it helps! random taglib

Also you may try $Math.random function.

Cioffi