I. J2EE's background 1, the needs of enterprise application frameworks are in many enterprise applications, such as database connections, mail services, transaction processing, etc. are some universal enterprise demand modules, and these modules are developed every time it is developed. If a person is completed, it will cause problems such as long development cycle and code reliability. So many big companies have developed their universal module services. These servic software series are intermediate. 2, in order to make specifications, it is necessary to make a norm, otherwise it is not possible to achieve the above demand, many companies have developed their own middleware, but they have different communication with users, causing users to unable to different companies. The middleware is assembled in a piece for yourself. Thereby generating bottlenecks. So the concept of standard. In fact, J2EE is a series of standards based on Java technology. Note: Intermediates interpret the middleware between operating systems and higher first-class applications. The function of him is: isolating the app runs the environment with the operating system, so that application developers do not have to worry about more system issues, but directly pay attention to the ability to solve the problem. The concept of the container that we will say later is one of the middleware. Second, the related noun interpretation container: act as a role of the middleware WEB container: Provides an environment in which the application component (JSP, servlet) is provided, allowing the JSP, Servlet to interact in the environment variable interface in the container, do not have to pay attention to other system problems . There is mainly a web server to achieve. For example: Tomcat, WebLogic, WebSphere, etc. The interface provided by the container strictly abides by the Web & NbsPApplication standard in the J2EE specification. We call the Web Server of the above standards called the web container in J2EE. EJB container: Enterprise & nbspjava & nbspBean container. More industry segments. He provides various management functions that run the component EJB. As long as the EJB that satisfies the J2EE specification is placed in this container, it will be managed by the container. And you can obtain system level services through ready-made interfaces. For example, email services, transaction management. The web container and EJB containers are generally the same, and more differences are isolated on the outside environment. Web containers are more in harmony with HTTP-based requests. The EJB container is not. It is more with databases, other services. But they are all interactive interactions with the outside to mitigate the burden on the application. For example, servlet does not have to care about the details of HTTP, directly reference the environment variable session, request, response, EJB does not have to care about database connection speed, various transaction control, and is done directly from the container. RMI / IIOP: Remote Method Call / Internet Object Request a Intermediary Agreement, which is primarily used for remote call services. For example, remotely running a program, which provides stock analysis services, we can implement them directly on your local computer. Of course, this is to communicate between heterogeneous systems through a certain specification. RMI is unique to Java. JNDI: Java Name Directory Service. The main functionality is: Provide a directory system that allows applications from all over its own index to meet the functionality of fast finding and positioning distributed applications. JMS: Java Message Service. It mainly implements communication between the various applications. Includes point-to-point and broadcast. JavaMail: Java Mail Service. Provides mail storage, transfer features. He is the core of implementing mail function in Java programming. The Exchange development package in MS. JTA: Java transaction service. Provide a variety of distributed transaction services. The application only needs to call the interface provided. JAF: Java Security Authentication Framework. Provide some security control frames. Let developers implement their own personal safety control strategies through a variety of deployment and customization. EAI: Enterprise Application Integration. It is a concept that involves a lot of technology. J2EE technology is a good integration implementation. Third, J2EE's superiority 1, based on Java technology, platform-independent performance highlights 2, open standards, many large companies have implemented application servers supported by this specification.
