J2EE and layered architecture

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J2EE
(Q). What is J2EE ?

 J2EE(java 2 Enterprise Edition) is one of the three Java platform
from sun micro system.

Other two’s are : (1) J2SE(Java 2 Standard Edition)

(2) J2ME(Java 2 Mobile Edition)

 J2EE is a collection of so many Java based technologies.
 J2EE technologies broadly divided into 2 catagories
o Component technologies
o Service technologies

Component technologies are :

o Servlets
o Jsp
o EJB(Enterprise java beans)

Servlets and jsp are known as web technologies
EJB is known as distributed technologies
A servlet and jsp are web components developed by web
component developers
EJB’s are develooped by business component developers .EJB’s
are knows as business components.

Service technologies are :

o JMS (Java Messaging Service)
o JTS (Java Transaction Service)
o JAAS (Java Authentication and autherisation Service)
o JNDI (Java Naming and directory Interface)
o Java Mail

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(Q). What is the purpose of J2EE ?

J2EE is meant for distributed,transactional,multi-tier and secured
enterprise application development.

(Q). What is Tier ?

 Physical seperations of components is nothing but a tier.

(Q). What is Layer ?

 Logical seperation of components is nothingbut a layer.

(Q). What is Web-Client ?

 Web resource shake request making software is known as web-
client
 Web-client is nothing but browser software
 Web-client is nothing but Http client because it uses Hyper text
transfer protocol to communicate with web-client

(Q). What is Web-server ?

 A web server is a server software that comprises 2 modules
1) Networking module(communication)
2) IO module
 Web server is a process not a software & hardware
 Web server is also known as http server forit’s uses hiper text
transfer protocol to communicate with browser
 Apache,IIS are 2 widely used web-servers
 Web-server process is running in which computer system,that
is known as web-server machine

Duties of web-server :


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 Providing Http socket connections to web-client
 Sending web-pages to the web-client
 Web-server can receive user inputs from the browser,but it
cannot process data.it cannot be communicate to be
database server.it cannot produce response pages to end-
user

(Q). What is Web-container ?

 Web-Container Container is a Server software that comprise
of 3 modules
Web server/http server/default handler
Servlet-Engine/servlet-container
Jsp-Engine/Jsp-container
 A web application is developed into the web container
 Installation/loading a web application into the web
container.so that it’s services are available to the web-client
is known as deployment.


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(Q). What is an Application Server ?

 Application server is a Server Software comprises of web container,EJB
Container and other enterprise services. Via.JNDI naming Services
JMS,JTS etc.,
Examples of some of Application Servers :

Weblogic8.1 / weblogic 10
JBoss
Sun Server
WebSphere(WAS from IBM)
GlassFish
Apache Tomcat

Different types of tiered Architecture are :
2-tier(Client-Server) Architecture
3-tier architecture
N-tier Architecture
Distributed Architecture

2-Tier (Client-Server)Architecture:

 2-tier architecture is also known as client-server architecture.
 In two tier architecture always server is the database
server(data layer).
 In such physical and data access layer run in one machine
which is nothing but client machine.


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2-tier architecture:
In a two-tier system, we have a client program and
a server program. The main difference between the two is that the
server responds to requests from many different clients, while the
clients usually initiate the requests for information from a single
server.
Dis-Advantage of 2-tier acrchitecture :

 Client side perfomance is very bad causes Fat(thick) Client


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3-tier architecture :
 Physical seperation of service layer(data access layer as
well) from the presentation layer is nothing but 3-tier
architecturre.
 One machine for one machine for service layer( and
DAL also) and another machine for presentation layer
is the actual physical seperation in this architecture.
 3-tier architecture eliminates client side
maintainance.it also makes the clients thin
 3 tier architecture does not make the client 100% thin.


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3-tier architecture:


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A three-tier application we have a client, a server and a database,
in which the server stores its data. The flow of information is
still essentially linear: a request comes from the client to the
server; the server requests or stores data in the database; the
database returns information to the server; the server returns
information back to the client

N-tier Architecture :

 An extension of 3-tier architecture is nothing but n-tier
architecture
 Service layer is one machine ;data layer in one machine;
presentation layer is in morethan one machine.i.e. windows
based enterprise application can be 3-tier architecture cannot
be ‘n’ tier as presentation layer runs in only one machine as
one process.
 Web-enabling a 3-tier architectural enterprise application is
nothing but making it n-tiered.


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Distributed Architecture :

 If business objects of a service layer are geographycally
dispresed in the network and still communicating with one
another such enterprise application is said to be distributed
appliaction and is said to have distributed tier architecture


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(Q). What are the different programming logics of the web
application..?

A Web Application has 3 logics

a. Presentation Logic
b. Business Logic
c. Application Logic
Code that generates input screens and representing pages for
the end-user is known as presentation logic
Data processing logic according to the business rules of the
oraganisation is nothing but business logic
Flow control logic is know as application logic

JSP –Model 1 Architecture :

Note : In this model, application logic and presentation logic is
mixed in the jsp. Only business logic is separated into the Java
bean.


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This architecture model is sufficient only for small applications
JSP –Model 2(MVC) Architecture :

Here Presentation logic is in view, application logic in
controller and business logic in model.
Clear separation of 3 logics give lot of benefits in application
development and maintenance.
(Q). what is MVC (Model-view-controller)..?

The main aim of the MVC architecture is to separate the business logic and
application data from the presentation data to the user.

Model: EJB/Spring/Java Beans
View : Jsp’s
Controller: Servlets /Struts


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Layer’s are 4 types:
Presentation or UI (User Interface) Layer (Struts/Jsps/JSF etc.)
Bussiness or Service Layer (Servlets/EJB/Spring)
Data Access Layer (ORM’s or JDBC)
Data Layer (Database)
Example for 4 layered architecture :


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J2EE and layered architecture

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