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EJB
Enterprise JavaBeans
EJB are write once, run any where, middle tier components
Logical Architecture
A EJB system is logically a three-tier system. The three tiers are
1. client
2. EJB server
3. Database
EJB’s Role
EJB specifies an execution environment
Container provides services in EJB
Container does not allow to access bean
directly from client

EJB Exists in the Middle tier
Business rules (Methods)

EJB Supports transaction processing
Container start a new transaction when the bean
is invokes
Bean be allowed to manage its own transaction

EJB’s Role
4. EJB can maintain states
Container keep track of state information
You can build states less EJB

5. EJB is Simple
Transaction processing
Persistent storage of state
Platform independent
Multitier architecture
“ Write once run anywhere”
EJB Logical Architecture
A EJB system is logically a three-tier system
The three tiers are as follows:
a) The Client
b) The EJB Server
c) The Database (or other persistent store)




Logical - because - these tiers may be single machines.
Cont…
EJB’s role in each of these tiers are:
a) Client side makes call to remote EJBs. The
client needs to know how to find the EJB server
and how to interact.

b) The EJB components live in the middle tier.
The EJB objects reside inside an EJB container,
which in turn resides in an EJB server.

c) EJB can access the database themselves,
typically via Java Database connecting (JDBC).

EJB’s Software Architecture
The diagram presents a high-level view of
the EJB architecture, showing the various
relationships between the various components.
Key Features of the EJB Architecture

EJB bean exists within the container

The bean and the client not directly access the
server – all access is performed against the container.

Rather it talks to the bean through its home
interface and its remote interface, both of which are
provided by the container.

EJB server handle requests for the container, and
feed the container incoming client requests.