Basics of JNDI

1
Basics of JNDI

• Alessio Bechini
• June 2002

2
Naming and Directory Services Rationale

• A fundamental element in every application is the
  capability to find and locate components and
  services.
• A client looking for a component/service usually
  knows its name, but not its physical location.
• The component name correspond to the actual name,
  typically much more difficult to remember and
  manage.
• A well-known naming service is provided on
  Internet by DNS.
• For applications, a naming/directory service is
  the way to get a reference to a required service
  (e.g. a JDBC data source, a JMS connection
  factory, an EJB home interface, etc.)

DNS
www.apache.org
64.208.42.41
3
Naming and Directory Services

• A naming service is an application that contains
  a set of objects, or references to objects,
  with corresponding names (usually easy to
  remember).Such correspondances are called
  bindings.
• A directory service allows for the association
  of attributes to a binding.
• Some popular directory implementations
• Lightweight Directory Access Protocol (LDAP)
• Network Directory Service (NDS)
• Network Information Servis Plus (NIS)

4
JNDI Overview

• JNDI (Java Naming Directory Interface) provides
  Java clients with the capability to access
  naming and directory services.
• JNDI is subdivided in the following packages
• javax.naming
• javax.naming.directory
• javax.naming.event
• javax.naming.ldap
• javax.naming.spi

JDBC APIs
JNDI APIs
JDBC Driver
SPIService Provider Interface
5
JNDI Configuration

• JNDI configuration could be a quite difficult
  task.
• Whenever we use an EJB server, JNDI is started
  automatically at the same time of the server
  itself. Such a service is usually already
  configured for the specific server.
• Also the client applications using JNDI must be
  configured, and this task is up to the
  programmer/assempler/deployer.

6
JNDI Environment Properties

• A client (object) uses JNDI to locate remote
  services but JNDI might be a remote service as
  well. Thus, how to locate a naming service
  without using a naming service?
• We can do it using environment properties.
• Some standard JNDI properties
• java.naming.factory.initial
• java.naming.provider.url
• Java.naning.security.authentication
• etc.

7
Context and InitialContext

• Context (interface) is used to deal with objects
  that have been bind to a JNDI name.
• javax.naming.Context contains methods to put
  objects in the naming service, and to retrieve
  them.
• All the naming services have an access point,
  and in JNDI it is named InitialContext.
• To obtain an InitialContext, three steps are
  required
• Select the service provider
• Specify every configuration needed
• Call the InitialContext constructor, providing
  the environment properties.
• !!! A unique InitialContext is not thread-safe!

8
Use of InitialContext

• InitialContext must be closed after its usage,
  as it happens for any resource, e.g. a JDBC
  connection. The best way to do it is to insert
  the invocation of the close method inside a
  finally block.
• The method getEnvironment of Context returns an
  Hashtable with all the active properties for the
  context.
• The method lookup(name) returns a reference to
  the Object corresponding to name. This way, also
  EJB home factories are looked up.

9
Access to the Environment of an EJB

• As an EJB usually must not access files, how can
  an EJB access its configuration properties?
• A smart way to pass a configuration value to a
  bean is through its deployment descriptor,
  adding an env-entry tag, e.g.
• ltenv-entrygt
• ltdescriptiongtwhat a beautiful
  entry!lt/descriptiongt
• ltenv-entry-namegttheNicestGirllt/env-entry-namegt
• ltenv-entry-typegtjava.lang.Stringlt/env-entry-type
  gt
• ltenv-entry-valuegtAnnelt/env-entry-valuegt
• lt/env-entrygt
• An EJB accesses environment properties using an
  InitialContext object, and looking up the
  desired property by its name.