Sample Application Architecture in Font

Generate ECC200 in Font Sample Application Architecture

Duke s Bank is a classic J2EE application composed of tiers commonly found when developing enterprise applications. It is packaged so that the modules corresponding to each tier are clearly separated. To simplify the code, we have slightly modified the Duke s Bank application, notably its packaging. For means of comparison, please refer to the original application, which is available on the Sun Microsystems web site.

Before we cover the details of the tiers, we ll provide an overview of the whole application and its organization in the sections that follow.

As J2EE advises, the application is composed of several tiers, as shown in Figure 10-1.

Figure 10-1. The Duke s Bank application s architecture The tiers and their roles are as follows: The data tier allows for storage of the persistent data and is implemented within the PointBase relational database. The business tier contains EJBs that implement the application s logic. These EJBs are the session EJB, which provides a client s view of the application s business logic, and the entity EJB, which represents the persistent objects manipulated by the application. The business tier directly accesses the data tier, especially through the entity EJBs. The presentation tier allows the application to be accessed through a browser. It contains a web servlet/JSP container and accesses the business tier. Relative to the business tier, the presentation tier can be considered as a specific Java client tier. The client tier can be either a web (thin client) or a Java application. In this case, it is a web application, as it accesses the presentation tier through HTTP; in the case of Java, it directly accesses the business tier for locating the EJBs and goes through RMI for remote communication. In the latter case, the Java client self-manages its presentation on the client site (thick client).

Although you can use any IDE, we recommend using the Eclipse open source IDE (we used Eclipse to develop the application presented in this chapter). Eclipse can be downloaded from http://www.eclipse.org. You can import the Eclipse project from the file system. The AJDT plug-in for AspectJ is required to compile it, and the installation of this plug-in is depicted in the appendixes. In contrast with the original application, we structured this application by separating the code into several independent projects. This structure allows developers to work more efficiently, especially in the case of a large project, where different teams could more easily be assigned to the development of a given tier.

The Eclipse projects are as follows: The Commons project contains all the classes common to several tiers. For example, it contains the transfer objects and the service locators, described later in more detail, which are used by the client, business, and presentation tiers. The BusinessUtils project contains all the classes used by the business tier. The BusinessComponents project contains all the business Plain Old Java Objects (POJOs). The EJBComponents project contains all the business EJBs. The ClientUtils project contains all the classes used by the client tier. The BusinessDelegates project contains all the delegates, described later in further detail, that allow the clients to access the business objects transparently with regard to the communication layer. The ApplicationClient project contains the client application and its logic. Figure 10-2 illustrates the project dependencies.

Figure 10-2. The project dependencies For further clarification on the Eclipse project s packaging, please refer to the screen shots later in this chapter, which show the internal organization of the tiers. Packages contain regular and aspectized application classes. This organization allows programmers to compare aspectized and regular code more efficiently, especially when using the AJDT plug-in and its aspect visualizer.