J2EE beginners need to understand

J2EE beginners need to understand

I. background of J2EE

1. Requirements for enterprise-level application frameworks
In many enterprise-level applications, such as database connection, mail service, and transaction processing, these modules are common enterprise requirement modules. If these modules are completed by developers every time they are re-developed, this will cause issues such as long development cycle and code availability. As a result, many large companies have developed their own general module services. These service software series are collectively referred to as middleware.

2. For general purpose, a standard must be put forward. Otherwise, the general purpose cannot be achieved.
Based on the above requirements, many companies have developed their own middleware, but their communication with users is different, as a result, users cannot assemble different middleware from different companies to serve themselves. This leads to bottlenecks. Therefore, the standard concept is proposed. In fact, J2EE is a series of standards based on Java technology.
Note: The Explanation of the middleware lies between the operating system and higher-level applications. The function is to isolate the application running environment from the operating system, so that application developers do not have to worry about more system problems, but directly focus on the application's ability to solve problems. The container concept we will talk about later is a kind of middleware.

2. Glossary

Container: acts as the role of Middleware
Web Container: provides an environment for the application components (JSP and Servlet) in the container, so that JSP and servlet can directly interact with the environment variable interfaces in the container, so that you do not have to pay attention to other system problems. It is mainly implemented by Web servers. For example, tomcat, WebLogic, and websphere. The interface provided by the container strictly complies with the Web application standard in J2EE specifications. We call the web server that complies with the above standards the Web Container in J2EE.

EJB container: Enterprise Java Bean container. More industry-specific characteristics. It provides various management functions for the component EJB running in it. As long as the EJB meeting the J2EE specification is put into the container, it will be managed efficiently by the container immediately. In addition, system-level services can be obtained through ready-made interfaces. For example, mail service and transaction management.

Web containers and EJB containers are basically the same in principle. The more difference is the isolated external environment. Web containers mostly deal with HTTP-based requests. The EJB container is not. It deals more with databases and other services. However, they all implement interactions with the outside world to reduce the burden on applications. For example, servlet does not need to care about HTTP details, but directly reference the environment variable session, request, and response. EJB does not need to care about database connection speed and various transaction control, which is directly completed by containers.

RMI/IIOP: Remote method call/Internet object request mediation protocol, which is mainly used to call services remotely. For example, if a program runs on a remote computer that provides the Stock Analysis Service, we can directly call it on a local computer. Of course, this requires certain specifications to communicate between heterogeneous systems. RMI is unique to Java.

JNDI: Java Naming directory service. The main function is to provide a directory system that allows applications from other places to leave their own indexes on it to quickly find and locate distributed applications.

JMS: Java Message Service. Communication between applications. Including point-to-point and broadcast.

Javamail: Java mail service. Provides mail storage and transmission functions. He is the core of the mail function in Java programming. Exchange development kit in equivalent Ms.

JTA: Java transaction service. Provides various distributed transaction services. An application only needs to call the interfaces it provides.

JAF: Java security authentication framework. Provides some security control frameworks. Developers can implement their own personalized security control policies through various deployment and customization.

EAI: Enterprise Application Integration. Is a concept that involves many technologies. J2EE is a good integration implementation.

Iii. Advantages of J2EE

1. Outstanding platform independence based on Java Technology

2. Open Standards many large companies have implemented application servers that support this specification. Such as BEA, IBM, and Oracle.

3. Provide professional general software services.

4. provides an excellent enterprise-level application framework, laying the foundation for rapid and high-quality development

Iv. Status quo

J2EE is an enterprise-level application specification developed by Sun. The current maximum version is 1.4. The application servers supporting J2EE include IBM WebSphere Application Server, BEA WebLogic Server, JBoss, Oracle Application Server, and Sun ONE Application Server.