13 core technologies of J2EE (1)

Java was first launched on browsers and client machines. At that time, many people questioned whether it was suitable for server-side development. Now, with the increase in third-party support for the Java2 Platform Enterprise Edition (J2EE), Java is widely accepted as one of the preferred platforms for developing enterprise-level server solutions.
The J2EE platform consists of a complete set of Services, application interfaces (APIs), and protocols. It provides function support for developing Web-based multi-layer applications.
In this article, I will explain 13 core technologies supporting J2EE: JDBC, JNDI, EJBs, RMI, JSP, Java servlets, XML, JMS, Java IDL, JTS, JTA, javaMail and JAF will also describe when and where to use these technologies. Of course, I would also like to introduce how these different technologies interact.
In addition, to make you better feel the real applications of J2EE, I will introduce these technologies in the WebLogic Application Server, a widely used product environment from BEA Systems. No matter whether you are new to WebLogic Application Server and J2EE, or project managers and system analysts who want to know what benefits J2EE can bring, I believe this article will be of great reference value.
Macro impression: Distributed architecture and J2EE
In the past, layer-2 applications-usually called client/server applications-were the most talked about. In many cases, the only service provided by the server is the database service. In this solution, the client program is responsible for data access, business logic implementation, display results with appropriate styles, pop-up preset user interfaces, and accept user input. The client/server structure is usually easier during the first deployment, but it is difficult to upgrade or improve. It is often based on a proprietary protocol, usually a database protocol. It makes it very difficult to reuse business logic and interface logic. More importantly, in the Web era, L2 applications usually do not have good scalability, making it difficult to adapt to Internet requirements.
Part of Sun's design for J2EE is to solve the defects of the L2 structure. Therefore, J2EE defines a set of standards to simplify the development of layer-N enterprise applications. It defines a set of standardized components and provides complete services for these components. J2EE also automatically handles many implementation details for applications, such as security and multithreading.
Using J2EE to develop N-layer applications includes dividing different layers in a L2 structure into multiple layers. An N-tier application A can provide A separate layer for each of the following services:
Display: In a typical Web application, the browser running on the client machine is responsible for implementing the user interface.
Dynamic generation and display: Although the browser can display some dynamic content, to be compatible with different browsers, these dynamic generation tasks should be carried out on the Web server, using JSP, Servlets, or XML (Extensible Markup Language) and (extensible style sheet language ).
Business logic: the business logic is applicable to Session EJBs (which will be introduced later.
Data Access: Entity EJBs and JDBC are suitable for data access.