O'Reilly - Java Message Service

Understanding JNDI
Java Message Service
JNDI is a standard Java extension that provides a uniform API for accessing a
variety of directory and naming services. In this respect, it is somewhat similar to
JDBC. JDBC lets you write code that can access different relational databases such
as Oracle, SQLServer, or Sybase; JNDI lets you write code that can access different
directory and naming services, such as LDAP, Novell Netware NDS, CORBA
Naming Service, and proprietary naming services provided by JMS servers.
In JMS, JNDI is used mostly as a naming service to locate administered objects.
Administered objects are JMS objects that are created and configured by the system
administrator. Administered objects include JMS ConnectionFactory and
Destination objects like topics and queues.
Administered objects are bound to a name in a naming service. A naming service
associates names with distributed objects, files, and devices so that they can be
located on the network using simple names instead of cryptic network addresses. An
example of a naming service is the DNS, which converts an Internet hostname like
www.oreilly.com into a network address that browsers use to connect to web
servers. There are many other naming services, such as COSNaming in CORBA
and the Java RMI registry. Naming services allow printers, distributed objects, and
JMS administered objects to be bound to names and organized in a hierarchy similar
to a filesystem. A directory service is a more sophisticated kind of naming service.
JNDI provides an abstraction that hides the specifics of the naming service, making
client applications more portable. Using JNDI, JMS clients can browse a naming
service and obtain references to administered objects without knowing the details of
the naming service or how it is implemented. JMS servers are usually be used in
combination with a standard JNDI driver (a.k.a. service provider) and directory
service like LDAP, or provide a proprietary JNDI service provider and directory
service.
JNDI is both virtual and dynamic. It is virtual because it allows one naming service
to be linked to another. Using JNDI, you can drill down through directories to files,
printers, JMS administered objects, and other resources following virtual links
between naming services. The user doesn't know or care where the directories are
actually located. As an administrator, you can create virtual directories that span a
variety of different services over many different physical locations.
JNDI is dynamic because it allows the JNDI drivers for specific types of naming
and directory services to be loaded dynamically at runtime. A driver maps a specific
kind of naming or directory service into the standard JNDI class interfaces. Drivers
have been created for LDAP, Novell NetWare NDS, Sun Solaris NIS+, CORBA
COSNaming, and many other types of naming and directroy services, including
proprietary ones. Dynamically loading JNDI drivers (service providers) makes it
possible for a client to navigate across arbitrary directory services without knowing
in advance what kinds of services it is likely to find.
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