J2EE platform introduction

Today, more and more programmers want to develop distributed transaction application systems for their enterprises with the help of the fast, secure, and reliable server technologies. If you have already worked in this field, you will be very clear that in today's world where e-commerce and information technology are rapidly developing and full of needs, enterprise applications must be designed, built, and operated with less money, faster speed, and less resources than ever before.
To reduce costs and quickly implement enterprise application design and development, the J2EE platform technology provides a component-based implementation path for enterprise application design, development, integration, and deployment. The J2EE platform provides you with an application design mode, reusable component capabilities, unified security mode, and flexible transaction control. You can not only bring new customer solutions to the market faster than before, in addition, the stand-alone and J2EE-based solution will not bind your product to any vendor's products and APIs.
This section describes the J2EE 1.3 platform and provides an overview of the J2EE tutorial. The J2EE tutorial uses an example-based method to describe the features and functions of the J2EE SDK 1.3. Whether you are a newbie or an experienced enterprise application developer, you will find that the J2EE tutorial combines the text example, when you create your own enterprise solution, valuable and easy-to-use knowledge base.
If you are just getting started with J2EE application development, this introduction is a good start point. Here you will learn about the J2EE architecture, get familiar with important terms and concepts, and find out how to start J2EE application programming, integration, and deployment.
Distributed Multi-layer applications
The J2EE platform adopts a multi-layer distributed application mode. This means that the application logic is divided into components based on functions, and different application components that constitute J2EE applications are installed on different servers, this division is determined by the layer in which the application component belongs to a multi-level J2EE environment. Figure 1 shows that two multi-level J2EE applications are divided into different layers described in the following table. The J2EE application section shown in Figure 1 represents the J2EE application component.
& #8226; customer layer components running on the customer Machine
& #8226; Web layer components running on the J2EE Server
& #8226; business layer components running on J2EE servers
& #8226; enterprise information system layer software running on the EIS server
As shown in Figure 1, J2EE applications can be composed of three or four layers. J2EE multi-layer applications are generally considered as three layers because they are distributed in three different locations: client machines, J2EE servers, databases, or backend traditional system servers. A three-tier architecture application is an extension of the standard client/server application architecture, that is, a multi-threaded application server is added between the client application and the background storage.
Figure 1 multi-layer application
J2EE application components
A J2EE application is composed of components. A J2EE component is a self-encapsulated functional software unit. It is integrated into J2EE applications through related classes, files, and communication with other components. The J2EE specification defines the following J2EE components: