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J2EE introduction

Today more and more developers want to write distributed transactional applications for the enterprise and leverage the speed, security, and reliability and server-side technology. If you are already working in this area, you know that in today’s fast moving and demanding world e –commerce and information technology, enterprise have to be designed, built, and produced for less money, with greater speed, and with fewer resources than ever before. To reduce costs and fast-track enterprise application design and development, the java 2 platform enterprise editions (J2EE) technology provides a component-based approach to the design, development, assembly and deployment of enterprise applications. The J2EE platform offers a multi-development, assembly and deployment of enterprise applications. The J2EE platform offers a multitiered distributes application model, the ability of reuse components, integrated extensible markup language (XML) based data interchange, a unified security model, and flexible transaction control. Not only can you deliver innovative customer solutions to market faster than ever, but also your platform independent J2EE components-based solutions are not tied to the product enjoy the freedom to choose the products and components that best meet their business and technological requirements.

Distributes multi-tired applications

The J2EE platform uses multi-tired distributed application model. Application logic is divided into components according to function, and various application components that make up a J2EE application are installed on different mechanism depending on the tier in the multi-tired J2EE environment to which the application components belongs.

Client-tier components run on the client machines

We-tier components run on J2EE server

Business-tier components run on the J2EE server

Enterprise information system (EIS)-tier software runs on the EIS server. J2EE multi-tired applications are generally considered to be three-tired applications because they are distributed over three different locations: client machines, the J2EE server machine, and the database or legacy machines ate the back end.

J2ee components

J2EE applications are made up of components. A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its related classes and files and that communicates with other components. The J2EE specification defines the following J2EE components.

Application clients and applets are components that run on the client

Java servlet and JSP technology are web components that run on the server

Enterprise JavaBeans (EJB) components are business components that run on the server

J2EE Clients

A J2EE client can be a web client or an application client

Web clients

A web client consists of two parts

dynamic WebPages(containing various types of markup language html xml and so on which are generated by web components running in the web tire and a web browser, which renders the pages received from the server

Applets

A Web page received form the web tier can include an embedded applet. An applet is small client application written in java programming language that executes in the java virtual machine installed in a web browser. However client systems will likely need the java plug in and possibly a security policy file in order for the applet to successfully execute in the web browser

Application client

A J2EE application clients run on a web client machine and provides a way for uses to handle tasks that require a richer user interface than can be provides by a markup language. It typically has a graphical user interface (GUI) created form Swing or abstract window toolkit (AWT) APIs, but a command line interface is certainly possible

Application clients directly access enterprise beans running in the business tire. However ,if the application requirements warrant it, a J2EE application client can open an HTTP connection to establish communication with a servlet running in the web tier.

J2EE Containers

Normally ,thin –client multi-tiered application are hard to write because they provide many lines of intricate code to handle transaction and the state management, multithreading, resource pooling and other complex low level details. The component based and platform independent J2EE architecture makes J2EE applications easy to write because business logic is organized into reusable components

Attention

From the study point of view to become J2EE professional you should learn basic java,applet javabeans,EJB,struts,swings.to study all these click the left side menu