J2EE LAYERED ARCHITECTURE

                                        J2EE LAYERED  AND 3 TIER ARCHITECTURE

What is J2EE?

J2EE (JAVA 2 Enterprise Edition) is one of the three java Platform from sun micro system.

Other 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.

                                Component technologies.

                                Service Technologies.

Component technologies are

1)Servlets  : are known as webtechnologies  developed by web component devolopers.

                         2)Jsp

                         3)EJB (EnterPrise Java Beans):  developed by business component developers

Service technologies are

                                1)JMS (Java Messaging service)

                                2)JNDI (Java Naming and Directory Interface).

                                3) JTS ( Java Transaction Service).

                                4) JAAS ( Java Authentication and autheristion service)

                                5) Java Mail.

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

Tier:  Physical separations of components

Layer: Logical sepertion of components.

Webclient:  nothing but browser software, web resource shake request making software is known as web client. It’s nothing but Http client because it uses Hyper  text transfer protocol to communicate with web-client.

Web server:  Webserver is  a Process not a software & hardware. It is also known as   http server for its uses hyper  text transfer protocol  to communicate with browser.

             Apache

             IIS,  

             Sun one,

             iPlanet, 

             IHS 

Web server is a server software that comprises 2 modules

1)      Networking module (communication)

2)      IO Module

Webcontainer:

Application Server: Application server is a server software that comprises of webcontaner,Ejbcontainer and other enterprise services. Via JNDI naming services  JMS, JTS etc…,

                1)Websphere

                2)Weblogic

                3)JBoss

                4)Apache Tomcat

                5)Glassfish

                6)Sunserver

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Two-Tier Architecture:

The two-tier architecture is like client server application. The direct communication takes place 

between client and server. There is no intermediate between client and server.

A 3-tier application is a program which is organized into three major disjunctive tiers. These tiers are:

• Presentation tier (Front end)
• Logical tier (Middleware)
• Data tier (Backend).

Presentation Tier / Client Tier / UI Tier

This is the top most layer of application where user performs their activity. Let’s take example of any application where user needs to fill up one form. This form is nothing nut presentation layer. In windows application windows form is presentation layer and in web application web form belongs to presentation layer. Basically user’s input validation and rule processing performs in this layer.

Middle Tier/Logical Tier/Business Tier

This is on top of presentation layer. As the name suggest, most of the business operation performs here. For example, after collecting form data we want to validate them with our custom business rule. Basically we define classes and business entities in this layer.

Data Tier

It is on top of Business Logic Layer Data Access Layer presents. It contains methods that helps business layer to connect with database and perform CRUD operation. In data access layer generally all database related code and stuff belongs to. Sometimes people use platform independent data access layer to fetch data from different database vendor.