8.2 JAVA EE WEB APPLICATION MODEL
The Java EE application model begins with the Java programming language and the Java virtual machine. The proven portability, security and developer productivity they provide form the basis of the application model. Java EE is designed to support applications that implement enterprise services for customers, employees, suppliers, partners and others who make demands on or contri-butions to the enterprise. Such applications are inherently complex, potentially accessing data from a variety of sources and distributing applications to a variety of clients.
The Java EE application model defines an architecture for implementing services as multitier applications that deliver the scalability, accessibility and manageability needed by enterprise-level applications. This model partitions the work needed to implement a multitier service into two parts: the business and presentation logic to be implemented by the developer and the standard system services provided by the Java EE platform. The developer can rely on the platform to provide solu-tions for the hard systems-level problems of developing a multitier service.
The Java EE platform uses a distributed multi-tier application model for enterprise applications. Application logic is divided into components according to function, and the various application components that make up a Java EE application are installed on different machines depending on the tier in the multi-tier Java EE environment to which the application component belongs.
Most Java Web database applications are three-tier client-server applications, which means that this kind of application can be built in three tiers or three containers: client container, Web server container and database server container. Java Enterprise Java Beans plays an additional role in business data management and processing in this three-tier architecture. However, in recent years, because of its complexity and time-consuming development cycles as well as undesirable output performances, some researchers recommend using Java EE without EJB.
In order to get a clearer picture of these two kinds of architectures, let’s first concentrate on the difference between them.