I. J2EE technology
What is Java2 Platform, Enterprise Edition?
J2EE is a new concept model that Sun has just launched, has an incapacirable advantage compared to traditional Internet application models. Many companies today need to expand their business scope, reduce their own operating costs, shorten their response time between them and customers, which requires a simple, fast service between enterprises, partners, and employees. Typically, applications that provide these services must be combined with the Enterprise Information System (EIS) and provide services that can be provided to more vast users. These services must have the following features: a. High availability: to meet the current global business environment B. Safety: Protect users' privacy and security of corporate data. Related and scalability: Guaranteed business transactions correct and quickly usually consist of distributed applications, including front-end data and back-end data sources, and one or several layers between them, these intermediate layers It provides features that combine commercial features and data to EIS. These intermediate layers separate the client from complex business logics, using ripe Internet technology to minimize the time spent on management. J2EE officially reduces the cost and complexity of developing such intermediate layer services, thus making the service can be expanded quickly and easier to face the pressure in the competition. J2EE implements its advantages by defining a standard structure, as follows: a. J2EE Application Programming Model ---- A standard design model B for developing multi-level, thin customer user program. J2EE Platform ---- a standard platform for integrating J2EE applications, specifying a series of interfaces and method 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 ---- The ability to demonstrate J2EE
2. J2EE application model
J2EE is designed to provide enterprise services for customers, employees, suppliers, and collaborators, which are born with complexity, they have to access various types of data and distribute a large number of clients. In order to better control, manage these applications, support a wide range of users to introduce in the intermediate layer, and the intermediate layer describes an environment that is tightly controlled by the company's information technology department. J2EE applications rely on the EIS layer to store business business data. These data and systems used to manage it are the core of the enterprise. Initially, the two-layer structure (Client-Server) application model will increase the scalability and a broader function, but unfortunately provide the user with the complexity of the EIS service, and then install and maintain business logic on each user computer. The problems caused by the management have become a big limit. The limitations in these re-double-layer structures have not existed in the three-layer structure. Nowadays, there is now a commercial function of services, but also to develop code accessing the database and other resources, which is very complicated because the server of each multi-layer structure has its own application model, so the formation has been experienced. The team will be difficult. In addition, as the service size is expanded, in order to reduce the expenditure and speeding the response speed, the base layer code is often modified. The J2EE application model defines a building model to make multi-storey applications to implement services, and eliminate the above problems, providing scalable, easy access, easy management methods. The J2EE application model divides the work of multi-layer structural services to two: developers realize business and expression logic, and system services for standards provided by J2EE platforms. Developers can rely on this platform for the system-level hardware issues encountered in the intermediate layer service, providing a solution J2EE application model for intermediate-level applications, feature, arbitrary operation (Write, Run Anywhere), this The standard model minimizes the cost of training developers. J2EE Application Model takes an important step by minimizing its complexity in the establishment of multi-storey applications, making it an important step in simplifying and accelerating applications. 3. Java technology foundation
The J2EE application model starts at the Java program language and Java virtual machines, and the increasing improvement of portability, security, and developer capabilities is the basis for application models. Application models typically include a JavaBean component model. JavaBean is more easier to write Java technology for normal functions, using JavaBean development tools to customize them, combine these components.
4. safety
When other application models need to have security in each program, the J2EE platform environment is defined when the security constraint is developed. The J2EE platform defines a standard public access control rule that has been defined and interpreted by the programmer when developing on the corporate platform. J2EE also needs to provide a standard registration mechanism so that the application does not need to mix these registration mechanisms and logic, the same work is to be executed in a large number of different environments without changing the source code. For example: J2EE application developers can specify several security levels (such as User, Superuser, Administrator), so they write code to check the current user rights level when the user accesses data. In the development phase, developers give multiple sets of user appropriate security levels, enabling applications to determine the limit level before performing restrictions.
5. middle layer
One of the main advantages of the J2EE application model is the multi-layer application in the intermediate layer. In the J2EE platform, the intermediate business function is implemented by enterprise JavaBean. These enterprise Beans allow service developers to focus on commercial logic and let EJB Server handle the complex work of transport stable and upgradeable services. JavaServerPages Technology and Servlets provide intermediate layer capabilities for Internet-type services that are easy to access to the client layer. JSP technology allows user interface developers to provide services to any browser user to any browser user. Servlets makes Java technology-based developers with greater freedom to provide full dynamic services in Java languages. 6. Client layer
The J2EE platform supports several types of customers. Many J2EE services are designed to browser user services that interact with the client with the client through dynamically generating HTML pages, and the form, while JSP and Servlets are formatted by making these business data through some way, making the client easier Take it with it. These clients can be JavaApplets running in the browser and Java technology-based programs. It should be noted that security is a key part of multi-layer structure, and security in J2EE is always solved by platform and administrators. In most cases, the server or client does not require developers and safety logic.
7. HTML page
In Java2, you can directly provide dynamic HTML pages to your user's browser, in JavaServerPage technology, inserting a Java code dynamic generating page in an HTML page in JavaServerPage technology, is a very easy task. In some examples, some services require some integrated code that can be implemented by adjusting JavaBean from JSP.
8. J2EE declaration
An important goal of the J2EE application model is to minimize the application. One way to achieve this is to improve the burden of running a normal task on the J2EE platform. These ordinary tasks include enforce an application's security target, performing its transaction processing, linking the components they need. J2EE provides a simple, disclosed way to illustrate these behaviors. These instructions are dispersed in each of the partial code and development descriptions, and the development description is part of the application package, which allows the application developer to change any component to change the application.
