One J2EE, in the current business application development, this word seems to have become an essential oral zen. The first two days and "boss" chat, talked about J2EE, she couldn't help but feel said that when we went out to talk about the project, we have to persuade customers to adopt J2EE architecture; but now, customers will take the initiative to tell us "Is it J2EE, not can't!" J2EE's popular visible. Come down, I want to combine my own learning experience to lead a bit of J2EE. What is the background of the born born in two j2ee? Java 2 Platform Enterprise Edition, that is, J2EE, defines the standards for developing multi-layer enterprise applications. It is not accidental, it is a product that accumulates mature under various conditions. One of the reasons: The huge success of Java language. In 1994, Java was born. Due to its simplicity of its language, "writing once, any run" advantage, as well as the rapid growth of Internet and intranet, prompting a large number of developers and IT agencies in their own projects using Java. In just a few years, Java's trend sweeps the world. Cause 2: C / S structure gradually transforms into multi-layer architecture. After brings huge flexibility, it also adds the complexity of the creation, testing, configuration, management, and maintenance application components. The emergence of the J2EE platform is just reduced these complexity. The reason is three: Enterprises, companies need to participate in the Internet, and various business have entered the network. The rapid growth of these enterprise-level applications prompted to support a strong, enterprise, web-centered application structure. Finally, in 2000, Sun and its partners (IBM, etc.) brought us J2EE to bring us J2EE. The most used is the most version of J2EE 1.3. So, what is the benefit of the J2EE platform? First, it created a range of criteria for enterprise computing needs, such as database links, messages, web components, corporate business components, and more, constitute a whole process of enterprise application development. Second, J2EE is based on open standards, providing the standard platform for development components, suitable for different suppliers, and users have more manufacturers. Again, J2EE shortens the product investment market time. Products are developed on the existing basic components, which get rid of their own business applications. In some information, some benefits mentioned, but I think the above three points should be the most fundamental benefits of J2EE to this world. What is the four J2EE? Say that it is a specific solution for companies defined by Sun Company. It provides a multi-level distributed application model and a series of development technical specifications. The J2EE architecture includes the following four levels: (1) Client Tier is the client layer. Used to interact with users and display information from the system to the user. Includes HTML users, Applet, and Java Application, etc. (2) The Web layer web layer consists of a web server and a web component. J2EE Web components include JSP and servlets. This layer is mainly used to process customer requests, call the corresponding logic module, and return the results in the form of dynamic webpage to the client. (3) Business Tier's core business logic of processing applications. Business components are usually implemented to run EJB components within the EJB container, EJB containers provide component lifecycle, manage persistence, transaction, and resource allocation. So this layer is also called EJB layer or application layer.
IV) Enterprise Information System Layer (EIS TIER) Handling Enterprise System Software, including enterprise basic systems, database systems, and other legacy systems. The EIS layer is a J2EE application and a non-J2EE application or an integrated connection point for the heritage system. Among them, the business layer and the web layer form the intermediate layer of the three-layer J2EE application. Fifth is an enterprise-class distributed application, J2EE defines a wealth of technical standards, including APIs. These APIs must be provided to application components. These technologies cover database access, distributed communications, security, and more. (1) Component technology: J2EE's core idea is based on components and containers. Components can be reused, shared, distributed. (2) Servlet: It is used to generate a dynamic page or accept the user request to generate a corresponding operation. For example, as a Controler in the MVC mode. (3) JSP: Provides a simple powerful tool for the user to write a dynamic page, actually running through the container to generate the corresponding servlet. (4) EJB: This is the core technology of J2EE, but it is not that J2EE is EJB. EJB includes three forms of session bean, entity bean. Among them, the Session Bean includes two types and stateless, which generally encapsulates the specific business logic; Entity Bean is divided into CMP and BMP, which is a persistent data object representation, directly corresponds to the table in the database, specifically developed The session bean and entity bean often need to be used; as for Message Driven Bean, it is called a message-driven bean, which is actually a package component for JMS applications. (5) JDBC: It is a development interface provided by the Java language provided by a specific database management system. It provides a generic mechanism for accessing the SQL database and storage structure to support basic SQL features. It includes four types of drivers: 1) Access to JDBC-ODBC bridges; 2) Accessing through database network libraries; 3) Accessing through middleware; 4) Pure Java drive, directly access. Among them, 1, 2, 4 belongs to the JDBC two-layer applications, and the third is the three-layer application of the JDBC and needs to configure the connection pool and data source in the application server. (6) RMI / IIOP: Remote method calls and Internet Inter-ORB protocols. (7) Java IDL: Call the API of the CORBA service. Integrate CORBA into the Java platform to provide interactive services. (8) JNDI: Java Names and Directory Interfaces, access the data in the enterprise naming and directory services. (9) JMS: Java message service, can use queue and the subject two messaging methods to reach an asynchronous transmission of messages. (10) Java security: Safety is an important part of the J2EE architecture, which is implemented through JaaS (Java Verification), JCE (Java Security Extension), JSSE (Java Security Socket Extension). (11) JTA: This is a set of affairs management APIs. The program can start, submit, rollback transactions, or the container and transaction manager interaction.
