J2EE is Sun has just launched a new concept of model, with the traditional model of Internet applications has unparalleled advantages in comparison.
Many of today's enterprises need to expand the scope of their businesses, reduce their operating costs, and customers to shorten their response time, which requires the existence of a simple and fast services to enterprises, partners and employees.
Typical that the provision of these services must be integrated with enterprise application software information system (EIS) to combine and to provide new users with a broader service. These services should have the following characteristics:
a. High-availability: to meet the current global business environment
b. Security: the protection of user privacy and security of enterprise data
c. Can be dependent and scalability: to ensure that business transactions are usually correct and rapid distribution of these services are provided by the composition of the application, including the front end and back-end data sources, as well as between them one or several layers, these intermediate layer provides a commercial function and the combination of EIS data and functions. These middle-tier to the client from the complexity of the business logic separated from the use of mature technology enables users INTERNET management by minimizing the amount of time spent.
Reduced official development J2EE middle-tier services that cost and complexity of the services thus can be carried out quickly and can more easily face the competition pressure.
By defining a standard J2EE architecture to realize its advantages, as follows:
a. J2EE application Programming Model ---- for the development of a multi-level, thin client users of the standard design process model
b. J2EE Platform ---- a standard platform for integration of J2EE applications, specify a range of interfaces and methods
c. J2EE Compatibility Test Suite ---- a set of compatible test components, to detect whether the product is compatible with the J2EE Platform
d. J2EE Reference Implementation ---- used to demonstrate the ability of J2EE
2. J2EE Application Model
J2EE is designed for customers, employees, suppliers, partners to provide enterprise-class services, such as applications with the complexity of nature, they will have to visit various types of data and distributed in a large number of clients.
In order to better control, management of these applications to support a wide range of business functions to users in the introduction of the middle layer, middle layer describes an enterprise's information technology sector tightly controlled environment.
J2EE applications that rely on the EIS layer to store business data. These data and to manage its system is the core of the enterprise.
Initially, the two-tier structure (client-server) application model promises to improve the scalability and wider, but, unfortunately, directly to the user the complexity of EIS services and re-installed on each user's computer and maintain the business logic caused by management problems has become a significant constraint.
Two-tier structure which no longer limited to the three-tier structure has no longer exists.
Today, demand for business development function, but also the development of access databases and other resources of the code, which is very complicated, because a multi-layer structure of each server has its own application model, so the formation of the development has been experienced team will be difficult. In addition, with the expansion of services, in order to reduce costs and speed up the response speed, but also frequently modify their grass-roots level code.
J2EE application model defines a multi-storey building models to allow applications to achieve service and eliminate the above problems and provides a scalable, easy to access, easy management.
J2EE application model to achieve the multi-layer structure of services is divided into two parts:
Developers to achieve business and the expression of logic, as well as by the J2EE platform provides standard system services.
Developers can rely on the platform for the development of middle-tier service encountered the problem of system-level hardware to provide solutions
J2EE application model for the middle-tier application compiler provides one of the characteristics of any operation (write once, run anywhere), this standard model to minimize the cost of training developers.
J2EE application model through the establishment of multi-layer applications to minimize the complexity of the Circuit, to simplify and accelerate the application development was an important step.
3. Based on java technology
J2EE application model started in java programming language and Java virtual machine, providing them with the continuous improvement of the portability, security, and capacity development of staff is the basis of the application model.
Model applications typically include JavaBean component model, JavaBean is prepared for the general features of the code based on Java technology easier to use JavaBean development tools can be customized visualization, combination of these components.
4. When the security model for other needs of the application process in each specific platform when security, J2EE platform environment so that when the security constraints in the development have been defined.
J2EE platform defines a standard access control rules in public, when the process in an enterprise platform when the procedure had been explained in the definition and division. J2EE is also a need to provide a standard mechanism for the registration of these applications do not have a registration mechanism and logic mixed, the same work to perform in a large number of different environments and who do not need to change the source code.
For example: J2EE application developers can specify a number of security level (eg, user, superuser, administrator), so they write code to check the current user-level permissions when users access the data. In the development stage, groups of developers to give users the appropriate level of security, so that applications can easily determine the X-rated before the implementation of restrictions.
5. Middle layer
J2EE application model is one of the main advantages of the multi-storey in the middle layer applications. J2EE platform in the middle layer business functions realized by the enterprise JavaBean.
Beans services of these enterprises to allow developers to focus on business logic, and let the EJB Server to deal with transmission of a stable, scalable services to the complexity of the work.
Servlets technology and JavaServerPages layer provides to its customers easy-to-access Internet-based services to middle-tier functionality. jsp user interface technology enables developers to more easily provide users with any browser dynamic page service. Servlets allow Java technology-based developer greater freedom to the Java language to provide complete dynamic services.
6. Client Layer
J2EE platform supports several types of customers.
Many J2EE services are designed for the browser user services, these services through the dynamically generated Html page and form to achieve interaction with the client, and Jsp and Servlets through the adoption of these business data in one way or another format, so that the client more easily to work with it. These clients can be running on the JavaApplet browser and Java technology-based procedures.
It should be noted that security is a key part of multi-layer structure, the security of the J2EE platform and administrators always to solve the problem. In most cases, the service side or client-side developers do not need logic and security.
7. Html page based on the Java2 customers can be achieved in the user's browser to provide direct services to Dynamic Html page, in JavaServerPage technology Html page by inserting Java code dynamically generated page is a very easy thing. In some cases, some services need a comprehensive code, who can call the JavaBean from Jsp methods to achieve.
8. J2EE statement
J2EE application model of an important goal is to minimize the application. This would be achieved by a method in the J2EE platform is to improve the running of the burden of common tasks, such a common task, including the mandatory application of the security objectives, the implementation of its transaction processing, link the components it needs.
J2EE provides a simple, open way to illustrate these practices. These notes were scattered on the various parts of the code description and development, application development is described as part of the package, the description of xml-based application development so that those who do not modify any components can be changed on the role of the application.
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