enterprise java b19

7/29/2019 Enterprise Java B19

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What is EJB?

EJB is a server-side component that encapsulates

the business logic of an application.

Business logic is the code that fulfills the purpose

of the application; In Banking application EJB

might implement the business logic in methods

called transferFund, checkingBalance.

EJB is not for end-user, EJB is a middleware forclient application


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Benefits of EJB

For several reasons, enterprise beans simplifythe development of large, distributedapplications. First, because the EJB container

provides system-level services to enterprisebeans, the bean developer can concentrate onsolving business problems. The EJBcontainerand not the bean developeris

responsible for system-level services such astransaction management and securityauthorization.


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Second, because the beansand not the

clientscontain the application's business logic,

the client developer can focus on the

presentation of the client. The client

developer does not have to code the routines

that implement business rules or access

databases. As a result, the clients are thinner,a benefit that is particularly important for

clients that run on small devices.


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Third, because enterprise beans are portable

components, the application assembler can

build new applications from existing beans.

These applications can run on any compliant

Java EE server provided that they use the

standard APIs


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When to Use EJB

You should consider using enterprise beans if yourapplication has any of the following requirements:

The application must be scalable. To accommodate agrowing number of users, you may need to distribute an

application's components across multiple machines.

Transactions must ensure data integrity. Enterprise beanssupport transactions, the mechanisms that manage theconcurrent access of shared objects.

The application will have a variety of clients. With only afew lines of code, remote clients can easily locateenterprise beans. These clients can be thin, various, andnumerous.


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Type of EJB

Session Bean

Message-Driven Bean

Entity beans have been replaced by JavaPersistence API


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What is Session Bean?

A key difference between session bean and other beantypes is the scope of their lives. A session beaninstance is relatively short-lived object.

Session bean instance is created when a client requestit, and ends when it finishing process the client request

Session bean instances are not share between multipleclients and do not represent data in database

Session bean is used for interacting with applicationclient

Session bean can implements business logic of anapplication


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Session Bean Sub Types

Stateless Session Beans

Is a session bean that do not hold state across

client request

When a client invokes the methods of a stateless

bean, the bean's instance variables may contain a

state specific to that client, but only for the

duration of the invocation. When the method isfinished, the client-specific state should not be

retained


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Stateful Session Bean

Is a session bean that hold the conversation state

of a specific client with the server

Its like Session object (HttpSession) on web

application

The state is retained for the duration of the client-

bean session. If the client removes the bean orterminates, the session ends and the state

disappears.


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When to Use Session Beans

Stateful session beans are appropriate if any

of the following conditions are true:

The bean's state represents the interaction

between the bean and a specific client.

The bean needs to hold information about the

client across method invocations.


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To improve performance, you might choose a

stateless session bean if it has any of these

traits:

The bean's state has no data for a specific client.

In a single method invocation, the bean performs

a generic task for all clients. For example, you

might use a stateless session bean to send anemail that confirms an online order, etc..


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Session Bean: Local and Remote

Interface

To invoked a session bean, a client need to

create the session bean object through its

interface

Session bean has 2 interface: local and remote


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When to use Local or Remote?

Use Local interface if the client is in one

packaging with the ejb (.ear)

Use Remote interface if the client is in remote

location or deploy separately with ejb (.war

and .jar)


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Session bean best practices

Choose your bean type carefully. Stateless sessionbeans will be suitable most of the time. Carefullyexamine whether your application needs stateful

session beans, because it comes with a price. Ifthe EJB client lies in the web tier, then usingHttpSession may be a better choice than statefulsession beans.

Carefully examine interface types for sessionbeans. Remote interfaces involve network accessand may slow down your applications.


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Try it


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Session Bean Pattern

Ensures that the common services are

supported by both Remote and Local

interfaces


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ServiceInterface

businessService()

businessService()

RemoteInterface LocalInterface

BeanImplementation


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Try it..

enterprise java b19

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