Hello dear friends. In this video, we will examine the application model and distributed multitiered applications. Let's begin with 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 contribute to the enterprise. Such applications are inherently complex, potentially accessing data from a variety of sources and distributing applications to a variety of clients. To better control and manage these applications, the business functions to support these various users are conducted in the middle tier. The middle tier represents an environment that is closely controlled by an enterprise's information technology department.

The middle tier is typically run on a dedicated server hardware and has access to the full services of the enterprise. 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 the following parts: The business and presentation logic to be implemented by the developer. The standard system services provided by the Java EE platform. Now that you are more familiar with the Java EE application model, let's discuss distributed multitiered applications. The Java EE platform uses a distributed multitiered application model for enterprise applications.

Application logic is divided into components according to function. The application components that make up a Java EE application are installed on various machines depending on the tier in the multitiered Java EE environment to which the application component belongs. As you can see in this image, there are two multitier Java EE applications divided into the tiers. Let's examine the image. Client tier components run on the client machine. An application client runs on a client machine and provides a way for users to handle tasks that require a richer user interface than can be provided by a markup language. An application client typically has a graphical user interface, GY, created from the swing or the Abstract Window Toolkit API, but a command line interface is certainly possible. For the second application, a web client represents dynamic web pages containing various types of markup language such as HTML, XML, etc, which are generated by web components running in the web tier.

Web tier components run on the Java EE server. Java EE web components are either servlets or web pages created using JavaServer Faces technology and or JSP pages. Servlets are Java programming language classes that dynamically process requests and construct responses. JSP pages are text-based documents that execute a servlet but allow a more natural approach to creating static content. JavaServer Faces technology builds on servlets and JSP technology and provides a user interface component framework for web applications. Static HTML pages in applets are bundled with web components during application assembly, but are not considered web components by the Java EE specification. Server side utility classes can also be bundled with web components, and like HTML pages are not considered web components. Business tier components run on the Java EE server.

Enterprise Information system, EIS, tier software runs on the server, and this represents our data source like Oracle, MS SQL or other databases. Although a Java EE application can consist of all tiers shown on the image, Java EE multitiered applications are generally considered to be three tiered applications because they are distributed over three locations: client machines, the Java EE server machine, and the database or legacy machines at the back end. Three-tiered applications that run in this way extend the standard two-tiered client and server model by placing a multi threaded application server between the client application and back end storage. Java EE applications are made up of components. A Java EE component is a self-contained functional software unit that is assembled into a Java EE application with its related classes and files and that communicates with other components.

The Java EE specification defines these Java EE components. Application clients and applets are components that run on the client, Java Servlets, JavaServer Faces, and Java Server Pages technology components are web components that run on the server. Enterprise Java Beans , EJB components, are business components that run on the server. I hope you now have a better understanding of distributed multitiered applications. In the next video, we will cover Java Enterprise Edition Containers. See you in the next video.