J2EE Summary-My Understanding of J2EE specifications

After learning J2EE videos, the three series of videos feel so difficult to understand, during the video, the general framework of J2EE and EJB has been recorded and organized. next we will summarize some key points in the learning process!

What is J2EE? To know what J2EE is, first understand what Java is?

Java isSimple, object-oriented, distributed, robust, secure, portable, superior performance, multi-thread, dynamicJava can be understood at three levels.

• Programming Language
• Development Platform

• Application Environment

 

Java versions are divided into the following three versions based on the development platform layer in the preceding three layers:

• It has limited functions and is used for embedded devices.

• J2se, which contains the original core class library, user desktop applications, and browsers. It is also the entry version of Java World.
• J2EE provides comprehensive functions for data processing and server applications.

 

At the beginning, I didn't have a clear understanding of J2EE. I simply understood that J2EE is an advanced version of j2se and can complete many tasks that cannot be completed by j2se. with the increasing video and the increasing understanding of J2EE.

Who is J2EE born?

In many enterprise applications, such as database connection, mail service, and transaction processing, these modules are common enterprise requirement modules. If each development process is completed by developers, this will cause issues such as long development cycle and code reliability. As a result, many large companies have developed their own general module services. These service software series are also called middleware.

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. For general purposes, standards must be put forward. Otherwise, standards cannot be achieved.

The above process can be described in the simple figure below.

 

Here we need to talk about the concept of middleware: middleware is located 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 often talk about is a kind of middleware.

To put it bluntly, Jzee is a series of standards based on Java technology.

What are the standards of this series?

I simply summarized the thirteen J2EE standards through the mind map. For example:

 

Now I know that J2EE is a set of standards, but how can I understand them? My understanding of the specifications is also vague. Now I simply understand some concepts and principles first. You only need to develop corresponding programs according to the specifications, your program will have a strong vitality.

According to some knowledge, some J2EE specifications are standard, while others are not standard. for servlet, It is a standard specification, so it will be recognized in JDK, the middleware developer will implement it, and others will develop applications according to this standard. some standards are not standards, and may become standards in the future. this is a dynamic process of development.

If we are connected with the knowledge we have learned before, we can also understand the design pattern as a standard or, however, it is a solution and specification for some common problems. If you follow these ideas and specifications, similar problems can be effectively solved. standards or norms are both an embodiment of abstract thinking. The purpose of learning J2EE norms and standards is the same as that of learning design patterns. They both absorb the excellent ideas and experiences of our predecessors. we often say that we stand on the shoulders of giants.

Further understanding is a reflection of Java's Object-oriented Thinking. Here we will try again to rub and understand the concept of Object-oriented thinking.