JBoss Modules Example – Modular Web Application

Michal JastakSeptember 26th, 2011Last Updated: October 21st, 2012

1 305 2 minutes read

Recently I read Why there is no standard for developing real modular web applications? by Patroklos Papapetrou (also featured in Java Code Geeks). Inspired by this article I decided to check JBoss Modules in action. This post describes my experiment step by step.

I’ve started with the following goal in mind – to create a web application using some service defined by my own JBoss module. The service prepared by me was pretty simple. I named it Echo Service:

package warlock.echo;
 
public interface EchoService {
 
    String echo(String param);
     
}

and placed into a separate jar file, named echo-api. Then I implemented this service:

package warlock.echo.impl;
 
import warlock.echo.EchoService;
 
public class DefaultEchoService implements EchoService {
     
    public String echo(String param) {
        return param;
    }
         
}

and placed the implementation in a new jar file, named echo-module. Having in mind that my web application should have knowledge of the service API only, not the specific implementation, I decided to go with the way described in Creating Extensible Applications With the Java Platform – that choice required adding to echo-module jar special file under: META-INF/services/warlock.echo.EchoService, holding the “pointer” to the service implementation (fully qualified name of implementing class).

At this point, I retrieved and unpacked JBoss Application Server 7, stepped into the unpacked JBoss, and then into the modules directory. In this directory I’ve added the following structure:

Two jar files visible here are mentioned above, module.xml file is the definition of my JBoss Module – named ‘warlock.echo’, and has the following content:

<?xml version="1.0" encoding="UTF-8"?>
 
<module xmlns="urn:jboss:module:1.0" name="warlock.echo">
 
    <resources>
        <resource-root path="echo-module-1.0.0-SNAPSHOT.jar" />
        <resource-root path="echo-api-1.0.0-SNAPSHOT.jar" />
    </resources>
 
</module>

After the completion of the JBoss Module definition, I’ve prepared a simple Spring Framework based application (which uses echo-api jar only during the compilation of project and doesn’t use the echo-module jar at all) with only one Controller:

package warlock;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
 
import warlock.echo.EchoService;
 
@Controller
@RequestMapping("/echo.html")
public class EchoController {
 
    @Autowired
    private EchoService service;
     
    @RequestMapping(method = RequestMethod.GET)
    @ResponseBody
    public String handleGet() {
        return service.echo("It workzzzzz!");
    }
}

As you can see, the Controller returns as response body the result of Echo Service call for some string. Now to the most important part – Echo Service definition in Web Application:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
 
    ...
 
    <bean class="org.springframework.beans.factory.serviceloader.ServiceFactoryBean">
        <property name="serviceType" value="warlock.echo.EchoService" />
    </bean>
 
    ...
     
</beans>

I know, one thing is bothering you :) – how the hell will Echo Service implementation be found if we don’t add either echo-api and echo-module jars to the Web Application?!

Well, this is the beauty itself ;) – We just need one more thing – WEB-INF/jboss-deployment-structure.xml file:

<jboss-deployment-structure>
    <deployment>
        <dependencies>
            <module name="warlock.echo" services="export" />
        </dependencies>
    </deployment>
</jboss-deployment-structure>

This way we tell JBoss that this application depends on the ‘warlock.echo’ module and the services defined in this module. The rest is pure JBoss Module magic ;)

Lectures for the dessert:

Reference: Modular Web Application based on JBoss Modules from our JCG partner Warlock at the “Warlock’s Thoughts” blog.

Related Articles :

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions