Create a shared lib directory and place this jar, and any other common jars files you might have there. If you are using Maven, then you already have it in the form of the local repo.
In Eclipse, create a classpath variable for this directory and then use it to reference your jar file in your projects. If you have multiple projects that meet these conditions, it will make life much easier. It also makes it easy to change the location of the root directory if you go from a local drive to a network one.
In the external app, you will also include this jar file from its shared location on the apps classpath.
