An option that is open to you is to load such resources with the ClassLoader, for example, using getClass().getResource("/myResources.properties"). This means that you can then simply include resources inside your JAR files.
Of course, if you are loading resources from a webapp within an EAR file, you can also use getServletContext().getResource() if your resources are underneath the WEB-INF directory of your web application.
Using a system property to directly reference the deployed location of an EAR file is not the best thing to do, simply because the app servers are free to copy and unextract the contents into a directory on deployment.
Hope that helps
Simon