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Spring Boot configuration of wro4j

How to configure wro4j (Web Resource Optimizer for Java) with Spring Boot using runtime mode and an HTTP filter, without any third-party Spring Boot starters.

Stanislav MiklikAugust 6, 2015

What is wro4j

wro4j (Web Resource Optimizer for Java) allows you to optimize your web resources. When developing rich web applications with multiple CSS/JS frameworks alongside custom code, bundling resources into fewer HTTP requests while minimizing and compressing content improves performance — particularly for mobile users.

wro4j operates in two modes: runtime and compile time. Runtime setup with an HTTP filter was chosen here for development convenience, avoiding the complexity of compile-time configuration and the need for additional Maven repositories.

Spring Boot Setup

wro4j lacks native Spring Boot support. Rather than adding third-party dependencies, manual configuration was implemented.

Maven Dependencies

<!-- wro4j -->
<dependency>
    <groupId>ro.isdc.wro4j</groupId>
    <artifactId>wro4j-core</artifactId>
    <version>1.7.8</version>
</dependency>
<dependency>
    <groupId>ro.isdc.wro4j</groupId>
    <artifactId>wro4j-extensions</artifactId>
    <version>1.7.8</version>
</dependency>

Configuration Class

Register a FilterRegistrationBean that reads wro4j properties from application.properties using the wro. prefix. The filter maps to /wro/* paths.

@Bean
FilterRegistrationBean webResourceOptimizer(Environment env) {
    FilterRegistrationBean fr = new FilterRegistrationBean();
    ConfigurableWroFilter filter = new ConfigurableWroFilter();
    filter.setProperties(buildWroProperties(env));
    fr.setFilter(filter);
    fr.addUrlPatterns("/wro/*");
    return fr;
}
 
private static final String[] OTHER_WRO_PROP = new String[] {
    ConfigurableProcessorsFactory.PARAM_PRE_PROCESSORS,
    ConfigurableProcessorsFactory.PARAM_POST_PROCESSORS
};
 
private Properties buildWroProperties(Environment env) {
    Properties prop = new Properties();
    for (ConfigConstants c : ConfigConstants.values()) {
        addProperty(env, prop, c.name());
    }
    for (String name : OTHER_WRO_PROP) {
        addProperty(env, prop, name);
    }
    log.debug("Wro4J properties {}", prop);
    return prop;
}
 
private void addProperty(Environment env, Properties to, String name) {
    String value = env.getProperty("wro." + name);
    if (value != null) {
        to.put(name, value);
    }
}

wro.xml Configuration

Place this file in the WEB-INF directory. It specifies resource groups that wro4j will bundle together:

<?xml version="1.0" encoding="UTF-8"?>
<groups xmlns="http://www.isdc.ro/wro">
 
    <group name="other">
        <js>classpath:static/jquery/jquery-1.10.1.min.js</js>
        <js>classpath:static/timeago/jquery.timeago.1.4.1.js</js>
        <css>classpath:static/slider/slider.css</css>
    </group>
 
</groups>

application.properties

# wro4j config
wro.preProcessors=cssUrlRewriting,cssImport,semicolonAppender,lessCss
wro.postProcessors=cssVariables,cssMinJawr,jsMin
# set to 1 second to check for resource changes
wro.resourceWatcherUpdatePeriod = 0
wro.ignoreMissingResources = false

Update

For non-WAR deployments, you need to override where wro.xml comes from. A sample project demonstrating the alternative wro.xml configuration approach for non-WAR deployments is available on GitHub.