Java originally made its debut on client machine and browser. With increasing third party support in java 2 , J2EE (Java 2 Enterprise Application ) technology is widely being accepted for server side enterprise applications. J2EE architecture is logically divided in to many tiers such as client tier, presentation tier, business tier, and database tier. It supports many APIs and protocol that provides the functionality to provide multi tier web application.
J2EE Client Tier
J2EE application supports many types of clients they can run on laptop, desktop, palmtop, or on cell phone. They may range from desktop big browser to cell phone mini browser, all they connect to world wide web from their intranet, through a wired network or wireless network.
Java client tier consists of application running on desktop, laptop etc and they connect to the application server directly using HTTP, FTP etc protocol. This requires only that the application must installed on the client machine. The web browser is the client application software used to connect to the application server.
J2EE Presentation Tier
A J2EE presentation tier consists of applications that prepare /format data to deliver the client tier, and and takes data from client side to send back end business process. This tier typically consists of J2EE components such as servlet, JSP that prepare data in HTML or XML to deliver to the client. This tier also provides portal services that can provide secure, customize and personalize business service.
The presentation tier components are often reusable components that can be customized and plugged into an application.
The business tier performs the main function of the application by implementing the business logic on the data processing, coordinating among multiple user and managing database resources. This tier consists of tightly coupled components such as EJB components or message driven beans. It performs the business work and send to the presentation tier for client side or send to the database tier or data tier. The EJB can be used to solve business logic, and it is used to create business object .
Resource Tier/ Data tier
This tear consists all the data/ information related to the business logic. The data may be be resource or directory information stored in Lightweight Directory Protocol or it can be persistent application data stored in the database management system. Generally the data-tier is installed on the separate machine. All the information stored on this tier are very important for organization so it may kept to another place.
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