Using Regular Expressions in JSP EL

Question

In EL expressions, used in a jsp page, strings are taken literally. For example, in the following code snippet

<c:when test="${myvar == 'prefix.*'}">

test does not evaluate to true if the value of myvar is 'prefixxxxx.' Does anyone know if there is a way to have the string interpreted as a regex instead? Does EL have something similar to awk's tilde ~ operator?

Answer 1

for using Pattern.matches inside a jsp page in my case it was enough to call java.util.regex.Pattern.matches(regexString,stringToCompare) because you can't import package in jsp

Answer 2

Simply add the following to WEB-INF/tags.tld

<?xml version="1.0" encoding="ISO-8859-1" ?>
<taglib version="2.1"
        xmlns="http://java.sun.com/xml/ns/javaee"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
        http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd">

    <display-name>Acme tags</display-name>
    <short-name>custom</short-name>
    <uri>http://www.acme.com.au</uri>
    <function>
        <name>matches</name>
        <function-class>java.util.regex.Pattern</function-class>
        <function-signature>
            boolean matches(java.lang.String, java.lang.CharSequence)
        </function-signature>
    </function>
</taglib>

Then in your jsp

<%@taglib uri="http://www.acme.com.au" prefix="custom"%>
custom:matches('aaa.+', someVar) }

This will work exactly the same as Pattern.match