Custom JSTL function to retrieve application version from Maven build metadata

functions.tld

<?xml version="1.0" encoding="UTF-8"?>
<taglib version="2.0" xmlns="http://java.sun.com/xml/ns/j2ee"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd">
    <tlib-version>2.0</tlib-version>
    <short-name>zfn</short-name>
    <function>
        <name>applicationVersion</name>
        <function-class>org.devnull.zuul.web.config.JstlFunctions</function-class>
        <function-signature>
            java.lang.String getApplicationVersion(javax.servlet.ServletContext)
        </function-signature>
    </function>
</taglib>

JstlFunctions.groovy

package org.devnull.zuul.web.config

import org.springframework.web.context.support.ServletContextResource

import javax.servlet.ServletContext

class JstlFunctions {
    static String getApplicationVersion(ServletContext context) {
        def mavenProps = new ServletContextResource(context, "/META-INF/maven/org.devnull/zuul-web/pom.properties")
        if (mavenProps.exists()) {
            def properties = new Properties()
            def stream = mavenProps.inputStream
            properties.load(stream)
            stream.close()
            return properties.getProperty("version") ?: "unknown"
        }
        else {
            return "development"
        }
    }
}

sample.jsp

<%@ taglib prefix="zfn" uri="/WEB-INF/tags/functions.tld" %>

Version: ${zfn:applicationVersion(pageContext.servletContext)}