It all depends on your needs. What’s more important to you? Speed? Memory footprint?
If you’re already using JDBC adapters elsewhere in your project, it seems like a no-brainer to use a DB table. Since the data is pretty static, enable cacheing for the service.
If you want to roll your own Java service, have your class initialise a static TreeMap (or hashmap if your objects aren’t Comparable), and make a getter method that reads from it.
#Integration-Server-and-ESB#webMethods#Flow-and-Java-services