How to develop a high quality Java EE system

There are more and more students in Java EE, the technology of Java-EE is constantly developing, and all kinds of concepts emerge, this article tries to explain these concepts to beginners from an easy to understand angle so as to master the learning direction of Java EE.

The first thing we need to know is that Java and EE are two different concepts, Java is not just a language, has represented a different huge camp with Microsoft, so Java sometimes refers to a genre of software systems, of course, currently mainly. NET and Java two major mainstream systems.

Java EE can be said to refer to the implementation of the database information system, the database information system from the early dBASE, to DELPHI/VB, such as C/s structure, developed to B/s (browser browser/server server) structure, and the Java EE mainly refers to B/s structure of the implementation.

Java EE is also a framework and standard, framework similar to the concept of APIs, libraries, but beyond them. If you need to learn more about the framework, you can start with design mode.

The Java EE is a fictitious big concept, the Java EE Standard mainly has three seed technical standard: The Web technology, the EJB technology and the JMS, talks about the Java EE should say finally must implement to these three sub concepts.

Each of these three technologies is applied in two parts: the container part and the application part, the Web container also refers to the Jsp/servlet container, if you want to develop a Web application, whether compile or run, must have Jsp/servlet library or API support (except jdk/ Outside the J2SE).

In addition to Jsp/servlet technology in Web technology, but also need JavaBeans or Java class to implement some functions or packaging to carry data, so the Web technology was initially nude for short Jsp/servlet+javabeans system.

When it comes to JavaBeans technology, it involves component components technology (component), which is the core foundation part of Java, and many software design concepts (design patterns) are implemented through JavaBeans.

JavaBeans is not part of the concept of Java EE, if a JavaBeans object is called by Web technology (that is, Jsp/servlet), then JavaBeans runs in the Java EE Web container, and if it is invoked by the EJB, it runs in the EJB container.

EJB (Enterprise JavaBeans) is a kind of promotion and specification of ordinary JavaBeans, because enterprise information system development needs a scalable performance and transaction, security mechanism, this can ensure enterprise system smooth development, rather than develop to a scale to replace a software system.

At this point, the JavaBeans component evolved to EJB, not to say that the previous JavaBeans form disappeared, which naturally formed two kinds of JavaBeans technology: EJB and Pojo,pojo completely different from the EJB concept, referring to the ordinary JavaBeans, And the JavaBeans does not cling to a certain framework, or simply say: This JavaBeans is created by you for this application alone.

Java EE application System development tools are many: such as JBuilder, Eclipse, and so on, the IDE is the first development tools, that is, their primary basic function is to develop JavaBeans or Java class, but if you want to develop the EE system, To implement either Web technology or EJB technology, it is possible to have some specialized module functionality (such as Eclipse needs Lomboz plug-ins), and most importantly, because the Java EE system is differentiated into containers and applications two parts, In any development tool to develop Java EE need to specify the Java container.

Java EE container is divided into web container and EJB container, Tomcat/resin is Web container; JBoss is the EJB container +web container, where the Web container is implemented directly using Tomcat. So the Web application you develop can run on both containers, and the WEB+EJB application you develop can only run on the JBoss server, and the commercial product websphere/weblogic and JBoss are of the same nature.

Java-EE containers are also called Java-EE servers, most of which are consistent in their concepts.

If your Java EE application database connection is obtained through Jndi, that is to say, it is obtained from the container, then your Java EE application System is basically independent of the database, if you have coupled the database JDBC-driven configuration in your Java application system, Then your Java EE application system has a database concept color, as a mature need to promote the Java application system, not recommended and specific database coupling, of course, how to ensure that the performance of Java EE application System is reflected in your design level.

The standard of the design and development of Java EE Application System is: decoupling, whether the functions of your application system can be completely separated from each other or not, and only in this way can the software design goals of maintainability and extensibility be embodied.

In order to achieve this goal, the emergence of various framework concepts, the Java EE Framework standard divides a system into the web and EJB main parts, of course, we are sometimes not based on this specific technology, but from the design of abstraction as a presentation layer, service layer and persistence layer, which separates the Java EE from a height, the three levels, To achieve decoupling.