J2EE how to understand?

One. J2EE is a new conceptual model that Sun has just introduced, with incomparable advantages over the traditional Internet application model.

1. Many companies today need to expand their business scope, reduce their operating costs, shorten the response time between them and their customers, which requires the existence of a simple, fast service in the enterprise, partners and employees.

2. Typically, the application software that provides these services must be integrated with the enterprise information system (EIS) and provide new services that can be provided to a wider range of users. These services should have the following characteristics:

a. High availability: to meet today's global business environment

b. Security: to protect the privacy of users and the safety of corporate data

c. Dependability and scalability: to ensure that business transactions are correct and fast

3. Typically, these services are comprised of a distributed set of applications including front-end, data-end, and back-end data sources, as well as a variety of other services. data end and back-end data sources and one or more layers between them, these intermediate layers provide the functionality to integrate business functions and data with the EIS

. These middle layers separate the client from the complex business logic and use sophisticated INTERNET technology to minimize the time spent by the user on administration.

4. J2EE formally reduces the cost and complexity of developing such middle-tier services, thus enabling services to be rapidly deployed and to face competitive pressures with greater ease.

5. J2EE realizes its advantages by defining a standard structure as follows:

a. J2EE Application Programming Model

---- a standard design model for the development of multi-tiered, thin client-user programs

b. J2EE

Platform---- a standard platform for integrating J2EE applications, specifying a set of interfaces and methods

c. J2EE Compatibility Test

Suite---- a set of compatibility test components used to test products for compatibility with the J2EE platform

d. J2EE Reference Implementation---- is used to demonstrate the capabilities of J2EE

II. J2EE Application Model

1. J2EE is designed to provide enterprise-class services to customers, employees, vendors, and collaborators, and such applications are inherently complex in the sense that they access a variety of data types and distribute them to a large number of clients. to a large number of clients.

2. In order to better control and manage these applications, business functionality to support a wide variety of users is introduced in the middle tier, which describes an environment that is tightly controlled by an organization's information technology department.

3. J2EE applications rely on the EIS tier to store an organization's business data. This data and the systems used to manage it are at the heart of the enterprise.

4. Initially, the two-tier architecture (client-server) application model promised increased scalability and broader functionality, but unfortunately, the complexity of delivering EIS services directly to the user and the administrative problems associated with installing and maintaining business logic on each user's computer became a major limitation.

These limitations of a two-tier architecture are no longer present in a three-tier architecture.

5.. Today's requirement to develop both the business functionality of the service and the code to access databases and other resources is complex because each multi-tiered server has its own application model, so assembling a team of experienced developers would be difficult.

This is because of the complexity of developing the business functionality of the service and the code to access databases and other resources. Also, as the service scales, its base code will have to be modified frequently in order to reduce expenses and speed up response.

Three. The J2EE application model defines an architectural model to allow multi-tier applications to implement services and eliminates the above problems by providing a scalable, accessible, and easy-to-manage approach.

1. The J2EE application model divides the implementation of multi-tier architectural services into two parts:

the developer's implementation of business and expressive logic, and the standard system services provided by the J2EE platform.

Developers can rely on the platform to provide

2. solutions to system-level hardware problems encountered in developing middle-tier services

The J2EE application model provides compile-once, run-anywhere features for middle-tier applications, and this standard model minimizes the cost of training developers.

The J2EE application model takes an important step in simplifying and accelerating application development by minimizing the complexity in building multi-tier applications.

3. Java Technology Foundations

The J2EE application model begins with the Java programming language and the Java Virtual Machine, which provide the foundation for the application model with their increasing portability, security, and developer capabilities.

The application model often includes a JavaBean component model. JavaBeans make it easier to write Java-based code for common functions, and development tools that utilize JavaBeans can visually customize and combine these components.

4. Security

While other application models require platform-specific security in each program, the J2EE platform environment enables security constraints to be defined during development.

The J2EE platform defines a standard set of publicly available access control rules that are defined and interpreted by the programmer when the program is developed on the enterprise platform.

J2EE also needs to provide a standard registration mechanism so that the application does not have to mix these registration mechanisms with the logic that the same work has to be performed in a large number of different environments without changing the source code.

For example, J2EE application developers can specify several security levels (e.g., user, superuser, administrator), and they write code to check the level of user privileges when

previously when a user accesses data. During the development phase, developers give multiple groups of users appropriate security levels so that the application can easily determine the level of restriction before performing the restricted operation.

5. Middle Tier

One of the main advantages of the J2EE application model is the multi-tier applications in the middle tier. In the J2EE platform, middle-tier business functions are implemented by enterprise JavaBeans.

These enterprise beans allow service developers to focus on business logic and let the EJB

Server handle the complexity of delivering stable, scalable services.

JavaServerPages

Technology and Servlets provide the client tier with easily accessible middle-tier functionality for Internet-based services. Jsp technology makes it easy for user-interface developers to provide services that serve dynamic pages to any browser user. Servlets allow Java-based developers greater freedom to provide fully dynamic services in the Java language.

6. Client Layer

The J2EE platform supports several types of clients.

Many J2EE services are designed as browser user services that interact with clients by dynamically generating Html pages and forms, while Jsp and Servlets are designed to make it easier for the client to work with these commercial data by formatting it in some way

. These clients can be JavaApplets and Java technology-based programs that run in the browser.

It is important to note that security is a key part of the multi-tier architecture, and in J2EE security is always addressed through the platform and administrators. In most of the cases there is no need for developers with security logic on the service side or client side.

7. Html page based clients

In Java2 it is possible to implement services that serve dynamic Html pages directly to the user's browser, and in JavaServerPage

technology it is an easy thing to dynamically generate a page by inserting Java code into the Html page. In some cases, some services require integrated code, which can be realized by calling JavaBean methods from Jsp.

8. J2EE declarations

An important goal of the J2EE application model is to minimize the application. One way to accomplish this is to increase the burden of running common tasks on the J2EE platform that include enforcing an application's security goals, performing its transaction processing, and linking the components it needs.

J2EE provides a simple, publicly available way to describe these behaviors. These instructions are dispersed in sections of code and in development descriptions, which are part of the application package, and these xml-based instructions allow the application developer to change the role of the application without modifying any of the components.