General purpose abstract class that describes an API for retrieving Locale-sensitive messages from underlying resource locations of an unspecified design, and optionally utilizing the MessageFormat class to produce internationalized messages with parametric replacement.

Calls to getMessage() variants without a Locale argument are presumed to be requesting a message string in the default Locale for this JVM.

Calls to getMessage() with an unknown key, or an unknown Locale will return null if the returnNull property is set to true. Otherwise, a suitable error message will be returned instead.

IMPLEMENTATION NOTE - Classes that extend this class must be Serializable so that instances may be used in distributable application server environments.