SERVICES OFFERED BY EJB

SERVICES OFFERED BY EJB

JSP, Servlets and JavaBeans and EJBs have their own web container. The container of
EJB provides certain built-in services to EJBs, which is used by EJBs to perform different

functions. The services that EJB container provides are:

• Component Pooling
• Resource Management
• Transaction Management
• Security
• Persistence
• Handling of multiple clients
 

i) Component Pooling
 

The EJB container handles the pooling of EJB components. If, there are no requests for a
particular EJB then the container will probably contain zero or one instance of that
component in the memory. If, the need arises then it will increase component instances to
satisfy all incoming requests. Then again, if, the number of requests decrease, the
container will decrease the component instances in the pool. The most important thing is
that the client is absolutely unaware of this component pooling which the container
handles

ii) Resource Management
 

The container is also responsible for maintaining database connection pools. It provides
us a standard way of obtaining and returning database connections. The container also
manages EJB environment references and references to other EJBs. The container
manages the following types of resources and makes them available to EJBs:
 

• JDBC 2.0 Data Sources
• JavaMail Sessions
• JMS Queues and Topics
• URL Resources
• Legacy Enterprise Systems via J2EE Connector Architecture
 

iii) Transaction Management
 

This is the most important functionality served by the container. A transaction is a single
unit of work, composed of one or more steps. If, all the steps are successfully executed,
then, the transaction is committed otherwise it is rolled back. There are different types of
transactions and it is absolutely unimaginable not to use transactions in today's business
environments.
 

iv) Security
 

The EJB container provides it's own authentication and authorisation control, allowing
only specific clients to interact with the business process. Programmers are not required
to create a security architecture of their own, they are provided with a built-in system, all
they have to do is to use it

v) Persistence 

Persistence is defined as saving the data or state of the EJB on non J-C volatile media.
The container, if, desired can also maintain persistent data of the application. The
container is then responsible for retrieving and saving the data for programmers, while
taking care of concurrent access from multiple clients and not corrupting the data.
 

vi) Handling of Multiple Clients
 

The EJB container handles multiple clients of different types. A JSP based thin client can
interact with EJBs with same ease as that of GUI based thick client. The container is
smart enough to allow even non-Java clients like COM based applications to interact with
the EJB system