Download Naming and directory services are one of the more important

JNDI
CS616
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Naming and directory services are one of the most important
aspects in the World Wide Web (www), and Intranets in corporations.
It
provides network wide sharing of information such as applications and
users.
Currently, there are many different naming services, and JNDI
works with most of them.
Interface.
JNDI stands for Java Naming Directory
It provides a way for different distributed application
components to locate each other.
JNDI also allows different Naming and
Directory services to work with each other smoothly.
Have you been to a library lately?
How do you look for a book?
I hope you don’t wander aimlessly up and down the aisles, searching
through all the shelves for the book.
This process is not efficient.
There are thousands upon thousands of books in any given library (the
large ones may have millions of books).
To make the patron’s life
easier (at least when they are looking for a book).
Most libraries today has, catalog that is computer based.
Information is stored in a database (or databases).
To look for a
particular book, you just go to a computer terminal, and search by
title, author subject, or half a dozen other ways.
Years ago, the
library housed a cumbersome bureau of drawers, a manual card catalogue
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system 3x5 inch cards were stored in alphabetic order.
themselves were also in alphabetic order.
The draws
Each card listed information
about the author, title, a description references to its location in
that library only.
By going to the card catalog first, you increased
your chances of actually finding the book, thus saving yourself precious
time.
A naming service in the computer industry or world can be compared
to the catalog method at your local library.
The naming service (the
Card catalog) will contain information and location of service and
points to them (the card, and books on the shelf).
Like a card catalog
of the old, the naming service gives the programs a tool to find the
information and resources that they need, so the program does not waste
time looking for the resources.
Without naming services, the program
will wonder aimlessly looking for what it needs, like patrons without
the card catalog wondering aimlessly up and down aisles.
There are numerous reasons why there is a need for a naming
service.
Without a naming service, nothing can be found.
search for a file?
Is it by its file name?
How do you
When you want to sent a
card to a friend through the US postal system, commonly known as snail
mail, you need to put your friend’s name and address on the envelop.
Otherwise, the postman will not know where to deliver your letter.
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This
is also a form of a naming service.
Along the same vein, when you send
an email, you must provide it with an email address or else the email
application will not know where to send your email. The result will be
receiving an error message.
Another comparison can be mode. Have you recently located a
telephone number, using the old fashion way by flipping through a
telephone book?
For instance, you will note, the yellow pages are in
alphabetic order (by last name). It lists the telephone number and
address of the person accordingly.
In the networking world, a Local
Area Network (LAN) will also have a directory, which usually consists of
the user who has signed onto the network, their email address, and the
length that they have been on the network.
To comprehend Naming and Directory services conceptually is
somewhat hard to do.
them separately.
To better understand, it is best to get to know
Therefore, the Naming concept and Directory concept
will be individually discussed at length and in detail.
There is note worthy Japanese proverb, which states: “What’s
in a name, but a way to distinguish oneself in the sands of life.
Hence, the Naming concept distinguishes individual objects.
major uses is mapping.
One of the
Mapping is the means by which the computer will
recognize “people friendly language” in its own computer language. One
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of the major uses is mapping.
For example, mapping something people can
easily understand such as Yahoo.com to something that the computer can
understand such as its IP address is a usage of the Naming Concept.
One
of the places where it’s most commonly used is in the World Wide Web /
Internet.
An additional example would be when you type in an Internet
address like www.mircosystemscorp.com (made up). The computer system
will not know what the address means, and will not be able to locate the
site.
In order to find the site, the www address needs to be converted
(translated) into an IP address.
The system that performs this service
is the Internet Domain Name System, otherwise known as DNS.
It maps the
Internet address for www.mircosystemscorp.com to an IP address like
195.39.29.5(made up).
The diagram below is a generic naming service [javaworld1].
The Client
(Other computers, or programs, or users)
Name
Binding
Name
Binding
Naming Service
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Name
Binding
A person’s name is usually in the following order: first, middle, and
last name such as Patrick B. Merrman.
You will not see it as B. Merrman
Patrick, which just does not make sense, at least in the United States.
In order to understand the names and be able to use the naming system,
it must have a naming convention, just like in real life.
The naming
convention may be different from among naming systems (B.Merrman Patrick
can be recognized as normal in another country).
The relationship
between an object and its associated name is called binding (see diagram
above).
Therefore,www.yahoo.com is bound to 176.23.5.6(made up).
Sometimes, the object associated with the name can not be stored
directly. The naming service only acts as pointers; it points to the
location of the object itself.
As in the library, the card catalog only
contains information about the book, and it points to the location of
the book on the shelves. Obviously, the book itself is not physically
located inside the card catalog draw.
This applies similarly to the
object that is physically located inside the naming service.
service will have information about accessing the object.
The naming
The
information will be very compact (like the information on a card
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catalog).
use it.
Usually, it contains the location of the object and how to
In the Webster’s II New College Dictionary context is defined
as “the part of a written or spoken statement that surrounds a word or
passage and that often specifies its meaning.”
simply means file directory.
In naming concepts, it
/windows/temp is a subcontext.
For example, /windows is a context, while
However, most people simply refer to it
as a directory and a subdirectory.
A system that puts the naming concept to actual use is a naming
system.
It is a group of contexts that must have the same naming
convention that is connected with common operations (the same operations
can be used on them).
The names in a naming system are called
namespace.
Comparing to naming concepts, Directory concepts are much easier
to understand.
Directory service is somewhat like an extension of the
naming service (which explains, why naming concepts was discussed
first).
It allows objects to have attributes, which further “defines
the object”.
The Human Resources Department at any given company will
have on its file information about their employees.
It maps the
employee’s social security number to his name, home address, and home
telephone number.
This is like the directory service for the computer,
except that the one for the computer is much more powerful, and can have
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multiple types of customers.
computers and programs.
They can include users (people), other
In addition, the information is store online
for easier access.
The relationship of an attribute with an object is simple.
The
attributes further explain and provide more information about that
specific object.
For instance, using the previously mentioned Human
Resource example, the employee’s social security number is the object.
His home phone number, address, name, and other information are
attributes describing the object.
There is also an attribute identifier and a set of attributed
values associated with each attribute.
explained in an example.
These two parameters can best be
In the Human Resource example, the home
address is the attribute identifier, while 236 West St. New York, NY
12345-6789 is the attribute value, which is unique.
Naturally, this
depends on the given attribute.
The diagram below is a generic directory service [javaworld2].
The
Client
Name
Entry
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Attr.
WWW.Dictionary.com defines directory as: “A description of the
various characteristics of a file…” A service that provides the ability
to create, add, remove, and modify an attribute is called directory
service.
There are many examples of directory service.
NDS, which
stands for Novell Directory service, and NIS, which stands for Network
Information Service are two examples of directory service, which are
related to Network.
One has information about the network and is for
Novell networks; the other is for Solaris operation systems.
Directory Service also allows searches to be done, and filters
to be applied.
If you are looking for an object by its name, then you
are doing a search.
However, if you are looking for objects that match
certain rules, and you are searching for the objects by doing a query on
its attributes, then you are using a search filter.
the filter is what is going to be found.
What you list in
For example, if you state all
objects with an email address, then the result of the search will be
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objects that contain an email address attribute.
This is also called a
reverse look up or content based search. These are the basic concepts of
Directory Service.
There many existing Naming and Directory services, and they vary
slightly from one another:

COS, Common Object Services, is a naming service for CORBA
applications. COS allows other applications to store and access
CORBA objects.

DNS, Domain Name System, is an Internet's naming service. As
explained earlier, it maps people-friendly names like
www.exit.com, to computer-friendly IP (Internet Protocol)
addresses (245.39.15.336). DNS’s service and underlying database
is spread across different hosts on the Internet (it’s
distributed).

LDAP, Lightweight Directory Access Protocol, is a striped down
version of the DAP.
LDAP was developed by the University of
Michigan.

DAP, Directory Access Protocol, is a standard for network
directory.
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
NIS, Network Information System, is a naming service also
developed by Sun Microsystems. It allows users to access files and
applications on any host with a single ID and password.
One of the major problems with these existing Naming and Directory
services is that there are so many of them.
resolving issues and naming conventions.
uniform naming conventions.
Each has their own way of
Consequently, there are no
As a result, this makes it hard for
different directory services to work together.
If a specific type of
Naming and Directory service needs to get information from another, it’s
difficult or sometimes even impossible.
JNDI, which stands for Java Naming directory interface, was
developed by Sun Microsystems (www.sun.com) and is an application
programming interface (API).
JNDI was developed by Sun as a regular or
standard extension to Java programming Language.
Currently, the latest
version of JNDI is 1.2, which is a major upgrade.
The initial purpose
of JNDI is to support and provide Java, as well as applications written
in Java programming language, with naming and directory service and
functionality needs (JNDI will run on all compatible platforms
supporting Java 1.1.6 or higher).
The existing Naming and Directory
service that was available at the time is very specific.
In other
words, each Naming and Directory service has their own rules, specs, and
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conventions.
Java Language is based on portability, the ability to work
on any operating systems or machine.
Therefore, a Naming and Directory
service that is not portable will not work. As a result, JNDI solves the
problems of incompatibility for the other Naming and Directory services.
JNDI is not a naming and directory per-say, but rather an interface. It
allows all different types of Naming and Directory services to work in
unison.
JNDI can be downloaded free of charge from www.java.sun.com.
It is everywhere you look (at least when using Java and Java
applications and Technologies).

Some of the more “well" known ones are:
JDBC, Java Database Connectivity package, is also an API
technology.
It allows you access any (well, almost any)
tabular data source from the Java programming language.
sources include spreadsheets and flat files.
These
JDBC will also
allow cross DBMS connections.

JMS, Java Messaging Service is also a Java API.
JMS will
allow applications to create, send, receive, and read
messages.
This API defines a “common sent’ of interfaces and
their semantics, which allows programs written in the Java
programming Language to “communicates with other messaging
implementations.
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
EJB, Enterprise Java Beans, is relatively new (about 2 years
old).
This new technology has become increasingly more
popular, and receives a big push from the user community,
platform providers, and Enterprise developers alike.
surprise. That EJB is another Java API.
It is no
It allows
participation in transactions by specifying which object and
which methods are transitional.
Since EJB is based the on Java
programming Language, it is very portable.
This is also the same site where you can download Java compiler
free of charge.
So how do JNDI bypass the problem requiring names to be specified?
Well, JNDI uses the Name Class. In addition, it has subclasses, which
are helper classes to “help it out”.
The Subclasses are in order and
these ordered subclasses are what a name class consists of.
By using
the name class and name subclasses, JNDI can work with names independent
of the underlying naming service.
Confucius, the ancient Chinese philosopher, once said, “I hear and
I forget, I see and I remember, I do and I understand”.
Below are
several JNDI codes used to perform some of the most common functions so
you will be able to “see” and hopefully help you to “remember”? Please
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note that for detailed explanations of these examples, go to the
official Java site, at: www.java.sun.com/products/jndi/examples.html.
-
When accessing the Directory using JNDI to retrieve the email
address of a person or object, the code is as follows:
Attribute attr=
Directory.getAttributes(personName).get(“email”);
String email = (String)attr.get();
-
When searching the Directory for people whose surname is “Fox”
in the Wiz organization, the code is as follows.
Foxes =
directory.search(‘o=Wiz,c=US’, “sn=Fox”,controls);
-
When looking up Objects using JNDI, such as a printer, the code
is as follows:
Printer
printer=(Printer)namespace.lookup(printerName);
Printer.print(document);
-
When browsing the Namespace using JNDI, this browser can
either be general purpose or be supplied by the application.
Below is an example of using JNDI to list the contents of a
particular level in namespace.
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The code is as follows:
NamingEnumeration list = namespace.list(“o=Widget,
c=US”);
While (list.hasMore())
{
NameClassPair entry =
(NameClassPair)list.next();
Display(entry.getname(),entryClassName());
)
Previously a generic naming, and a generic directory diagram was
discussed.
Below is the JNDI Architecture diagram:
The user, progrmmer
The Server
Java Application
JNDI
JNDI API
API
Java
interface application
application progrmming
programminginterface
interface
Javanaming
namingdirectory
directry interface
Naming
Naming Manager
Manager
JNDI SPI
JNDI SPI
LDAP
LDAP
DNS
DNS
NIS
NIS
RMI
RMI
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CORBA
CORBA
There are three layers in JNDI: JNDI API, JNDI SPI, and Naming
manager, which manage the relationship between JNDI API and JNDI SPI.
It has two exposed interfaces called client and server. Note the client
may also be programming in Java, which has JNDI as one of its standard
extensions. The Java will use the JNDI API to access the different
implementation possibilities down in JNDI SPI, which stands for service
provider interface.
This is managed by the naming manager. However, the
client does not have to use the Java application in order to use JNDI.
The client can access JNDI directly.
The table below, which can be
found at www.java.sun.com/products/jndi/serviceprivider.html, provides a
list of publicly available service providers.
JNDI 1.2 Service Providers
LDAP
1.2.2 maintenance of Sun’s LDAP Service Provider, supporting versions 2 and 3
of the LDAP protocol
COS
Naming
RMI
Registry
NIS
1.2.1 maintenance release of Sun’s service provider for COS Naming, providing
access to CORBA naming services through the standard JNDI interface
1.2.1 maintenance release of Sun’s service provider for the RMI Registry.
DSML
DNS
1.2.1 maintenance release of Sun’s service provider for NIS, the Network
Information Service (formerly known as YP)
Technology preview 2 release of Sun’s service provider for Directory Services
Markup Language (DSML)
Technology preview 2 release of Sun’s service provider for the Domain Name
System (DNS)
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File
System
1.2 Beta 3 release of Sun’s service provider for accessing the file system
Novell
For access to the industry leading directory service NDS, and to NetWare 3X’s
Bindery, the Novell File Systems, and other Novell services such as Extended.
One of the biggest advantages of the Java Naming Directory
Interface is that it works with many other service providers. JNDI is
independent of any specific directory protocol.
It is the individual
service providers (such as, LDAP, NDS, and NIS, just to name a few) who
determine the protocol to support.
JNDI with all its advantages is
still an interface and not a full blown Naming and Directory service.
Therefore, it is not as powerful as LDAP, which is a “real” Naming and
Directory service and implementation.
This has some disadvantages.
order to understand something, you need hands on practice.
In
Yon can not
“play” with the Java naming and directory Interface if you do not know
other “full fledge” naming services.
Even if you do know another naming
and directory service, you still can not play with JNDI unless you have
access to an existing naming service.
This makes it difficult for
people who actually want to learn it.
An Old Latin proverb once said:
“To truly understand one must be doing it.” Java’s naming and directory
service interface (revolving around a small number of classes and not
many operations) is not as powerful as the other ones, such as LDAP.
For more functions you still need a real naming and directory service to
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do the job.
However, this can also be an advantage. For instance, it
allows JNDI to integrate smoothly, seamlessly, and effectively into an
existing computing environment, which also has a pre-existing naming and
directory service.
own.
Also, JNDI does not have security features of its
If you don’t have pre-existing security features, then don’t
expect JDNI to fulfill this need.
However, the Java naming and
directory Interface will allow applications to work with security
features that are already available with your pre-existing naming and
directory service.
In conclusion, Java’s naming and directory interface successfully
marketable.
There does not seem to be any need for major improvements,
except for adding a service provider to its list of integrated naming
and directory services.
features of its own.
Perhaps, another improvement would be security
It is an additional plus that JNBI works well with
other security systems, especially since security is such an important
aspects of any application. Due to the uniqueness of JNDI and its
ability to work well with other naming service it should not stay as an
interface for long.
Most likely in a few short years, JNDI will blossom
into a full-fledged naming and directory service boasting its added
capability of integrating smoothly with other naming and directory
services.
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Work Site
http://www.javaworld.com/javaworld/jw-01-2000/jw-01-howto.html[javaworld1].
http://www.javaworld.com/javaworld/jw-02-2000/jw-02-howto.html[javaworld2].
http://java.sun.com.products.jndi/tutorial/getstarted/overview/index.html
http://www.javaworld.com/javaworld/jw-03-2000/jw-0331-howto.html
http://java.sun.com.products.jndi
http://spectral.msc.mu.edu/javadev/jndi/overview-summary.html
http://www.weblogic.om/docs/classdocs/API_jndi.html
http://www.javaworld.com/javaworld/jw-07-1999/jw-07-cooltools_p.html
http://java.sun.com/j2se/1.3/docs/api/javax/naming/context.html
http://www.javaworld.com/javaworld/jw-07-1999/jw-07-cooltools_p.html
http:/www.persistence.com/powertier/devpit/documentation/programming/jndi-ch1.html
http:/www.persistence.com/powertier/devpit/documentation/programming/jndi-ch2.html
http:/www.persistence.com/powertier/devpit/documentation/programming/jndi-ch3.html
http:/www.persistence.com/powertier/devpit/documentation/programming/jndi-ch4.html
http:/www.persistence.com/powertier/devpit/documentation/programming/jndi-ch5.html
http:/www.persistence.com/powertier/devpit/documentation/programming/jndi-ch6.html
http:/www.dicinoary.com
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