Introduction to Java EE EJB Component

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Introduction to Java EE EJB Component

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This presentation deeply discusses the usage of EJB component in Java EE architecture.
Before start reading about EJB, it is advisable to understand the history behind
component-container architecture.
Introduction

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The WWW technology is moved from 2 tier to 3 tier, 3 tier to n-tier and now n-tier to
SOA based solutions for easy integration and maintenance.
Evolution of Component-Container Architecture

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Single Tier
Mainframe based systems where presentation, business logic and database are on
same node.

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Two-Tier
Client-Server model where presentation logic is moved to client machine.

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Three-Tier
Introducing browser based applications where web server will handle all requests.
Presentation, Business Logic and Database are separated.

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N-Tier
Introducing component-container approach with application server to run business
logic components. Presentation, Business Logic, Integration (Data/Legacy) and
Database.

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SOA
Service Oriented Architecture to interact with other systems. Both WSDL based SOAP or
JSON based web services are getting more popular in current trend.

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Normally, in N-Tiered applications we need to handle transaction and state management, multi-
threading, resource pooling, and other complex low-level services. The component-based and platform-
independent Java EE architecture simplifies these services with the help of containers. We just need to
write business logic and it is organized into reusable components.
The Java EE server provides underlying services in the form of a container for every component type.
Because we do not have to develop these services, we are free to concentrate on solving the business
problem at hand.
Java EE Containers

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EJB is a component to write business logic in an enterprise application and it runs inside a container
named EJB container. The typical Java EE application server architecture is shown below:
Introducing EJB Component

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The run-time portion of a Java EE product. A Java EE application server provides EJB and Web
containers.
Java EE Application Server

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Manages the execution of EJBs for Java EE applications. Enterprise beans and their container run on the
Java EE application server.
Enterprise JavaBeans (EJB) container

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Manages the execution of JSP page and servlet components for Java EE applications. Web components
and their container run on the Java EE application server.
Web container

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Manages the execution of application client components. Application clients and their container run on
the client.
Application client container

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Java EE provides the following EJB components.
1. Stateful Session Bean
2. Stateless Session Bean
3. Singleton Session Bean
4. Message Driven Bean
Note that Singleton bean is under session type introduced in Java EE 6.
EJB Components

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Using Stateless Session Beans
You are developing a business component where it does not contain the data for a specific client. Your
search component will be a best example for this scenario. Note that search requires only one method
invocation with search query among all the clients to perform the generic task (executing search query
on server side).
Example: Google search, Yahoo search and MSN search.
The following contents are taken from Oracle:
When to use Stateful Session Bean:
If the bean does not contain the data for a specific client.
If there is only one method invocation among all the clients to perform the generic task.
EJB Design Decision

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Using Stateful Session Beans
You are developing a business component where it wants to hold information about the client across
method invocation. The most common example for this type of implementation would be “Shopping
Cart”, where it needs to hold client specific information.
Example: Gmail, Yahoo Mail and Facebook.
When to use Stateful Session Bean:
What the bean wants to holds information about the client across method invocation.
When the bean works as the mediator between the client and the other component of the application.
When the bean have to manage the workflow of several other enterprise beans.
EJB Design Decision

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Using Singleton Session Beans
You can easily decide by the name itself, when you want to have exactly one instance of a session bean
go for Singleton session bean. You are developing an application where you want to have some
configuration parameters needs to be used across different modules and they needs to be available
during your server startup. You can easily implement this scenario by using Singleton Session bean.
When to use Singleton Session Bean:
State needs to be shared across the application.
A single enterprise bean needs to be accessed by multiple threads concurrently.
The application needs an enterprise bean to perform tasks upon application startup and shutdown.
The bean implements a web service.
EJB Design Decision

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Using Message Driven Beans
Unless like regular Java method calls MDBs are called asynchronously without blocking. Note that Java
EE 6. Note that Session beans allow you to send JMS messages and to receive them synchronously but
not asynchronously. To avoid tying up server resources, do not to use blocking synchronous receives in
a server-side component; in general, JMS messages should not be sent or received synchronously. To
receive messages asynchronously, we should use a message-driven bean.
EJB Design Decision

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One better way to study EJB is by taking Oracle’s Java EE 7 Developer Certification.
Prepare for your Java EE 7 Application Developer Certification using MyExamCloud course:
https://www.myexamcloud.com/onlineexam/1z0-900-mock-exams-ocp-java-ee-aplication-developer.course
Java EE 7 Developer Certification

Introduction to Java EE EJB Component

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