The contract negociation went through, the SLA is signed, and as a super-keen developer, you've already downloaded and built Elastic Path within minutes ()! Your heart is racing. The adrenaline is pumping. You just can't wait to start building your ecommerce storefront. With the source code in hand, it's so tempting to start hacking the Elastic Path source code right away.

But then you start thinking about the next EP release version, and bug fixes... and you're wondering what you're going to do when it's time to upgrade... How will you manage your customizations while keeping in sync with the most recent stable release of Elastic Path?

Maven to the rescue! You can use the power of Maven dependencies and, more importantly, the WAR overlay feature to do this. Overlays are used to share common resources across multiple web applications. Basically, it's a nice and clean way to apply the Decorator pattern to any EP based web applications.

How It Works

Step 1. If you don't already have one, install your own Maven repository (Sonatype Nexus, for instance). I won't go into details, but have a look at this old post on TheServerSide.com: Setting Up a Maven Repository.

Step 2. Deploy all required libraries shipped with the EP source code in your new Maven repository and build the codebase as per the Developer Guide. When it's done, you should have all applications packaged and ready to be deployed. Depending on your chosen Maven repository, you will need to deploy your different WAR packages (cmserver, searchserver and storefront) by uploading both the WAR binary and the POM file within the project.

Step 3. Create a WAR Maven project to hold all the customizations that you want to make on the standard storefront source code (controller, XML configuration, etc.) and specify that you are dependent on EP's Mavenized storefront WAR as follows:

<dependency>
     <groupId>com.elasticpath</groupId>
     <artifactId>com.elasticpath.sf</artifactId>
     <version>6.1.1</version>
     <type>war</type>
</dependency>

In your POM project file, add   the Maven Warpath plugin. The Warpath plugin extends the existing war overlay functionality included in the Maven War plugin to turn war artifacts into fully fledged build dependencies. We need it to expose the classes built and contained within the WAR dependency.

<plugin>
     <groupId>org.appfuse</groupId>
     <artifactId>maven-warpath-plugin</artifactId>

     <extensions>true</extensions>
     <executions>
          <execution>
            <goals>
                 <goal>add-classes</goal>
            </goals>
          </execution>
     </executions>
</plugin>

WAR overlay gives you full control and dependency management on all your EP customizations. In case of an upgrade or bug fix, all you need to do is rebuild the default EP package and update your project dependency. No more code merge nightmares! No more wondering if you missed any updated configuration files!

By combining the WAR overlay approach with Spring framework's plugin capability available within EP, you can override even bean implementation by simply creating your own core extension jar project, having a dependency on the standard EP core jar library, and defining a plugin.xml file within your own jar project. All this has already been proven in the field. You can implement your own storefront without modifying any EP core domain interfaces, services by injection you own implementation.

And voila! By leveraging Maven dependency and WAR overlay mechanisms, you have a clean, straightforward approach to implementing EP in the field that keeps the upgrade effort low.