Constant services locator

A typical ServiceLocator takes a JNDI directory name from the client and performs the requested lookup. This creates a coupling between all the various client calls to the locator and the directory structure—and when the directory structure changes, the client must be updated in many places. One variation of the ServiceLocator defines a constant set of services and lets clients access those services with a locator-specific name. This decouples the clients from the actual directory structure, allowing access to the new directory with only a single change to the locator.