Database Reference
In-Depth Information
submissions, manage state within an application, generate Web-page content, and control navi-
gation between pages. Many of the functions within this layer can be automated through con-
figurable foundation components.
11.2.3.1.2 Service-Based Architecture
Business processes are modeled by service components that comprise the Service-Based
Architecture. In J2EE platform, this is typically implemented as a process-oriented object wrapped
with a stateless Session Bean. The concept of services allows the front end to be decoupled from
the back-end business object components. The service-based layer adds tremendous value in terms
of flexibility, reusability, and component design.
11.2.3.1.3 Business Object Architecture
Business entities are modeled by object components that comprise the Business Object
Architecture. Each of these components manages the data and business logic associated with a
particular entity, including persistence of that data into a relational database. In J2EE platform,
this is typically implemented as a combination of regular Java classes and Entity beans in J2EE
application. The database access can be implemented by the container in the case of Container-
Managed Persistence (CMP) Entity Beans or by the developer in the case of Bean-Managed
Persistence (BMP) Entity Beans or regular Java classes. The persistence of each business object is
abstracted out to the extent possible so that separate data objects, persistent frameworks, or CMP
services can be used to affect the data object persistence in the database.
A major portion of the reference architecture is a generic and configurable implementation of
the Model 2 architecture discussed later in the following section.
11.2.3.2 Realization of the Reference Architecture in J2EE
The Java Enterprise Edition (J2EE) platform provides a component-based approach to implement
N-tier distributed enterprise applications. Figure 11.2 shows how the J2EE components provide
the implementations for the different layers of the reference architecture.
The components that make up the application are executed in runtime environments called
containers. Containers are used to provide infrastructure-type services such as life-cycle manage-
ment, distribution, and security. Containers and components in the J2EE application are broadly
divided into three tiers. The client tier is typically a Web browser or alternatively Java application
client. The middle tier contains the two primary containers of the J2EE application, namely, Web
container and EJB container. The function of the Web container is to process client requests and
generate corresponding responses, while the function of the EJB container is to implement the
business logic of the application. The Enterprise Information System (EIS) tier primarily consists
of data sources and a number of interfaces and APIs to access the resources and other existing or
legacy applications.
11.2.3.2.1 JavaServer Pages and Java Servlets as
the User Interaction Components
JavaServer Page (JSP) and Java Servlets are meant to process and respond to Web user request.
Servlet provides a Java-centric programming approach for implementing Web tier functionality.
The Servlet API provides an easy-to-use set of objects that process Hypertext Transfer Protocol
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