Overview of Enterprise Applications
This section describes enterprise applications and how they are designed and developed.
As stated above, the Java EE platform is designed to help developers create large-scale, multi-tiered, scalable, reliable, and secure network applications. A shorthand name for such applications is “enterprise applications,” so called because these applications are designed to solve the problems encountered by large enterprises. Enterprise applications are not only useful for large corporations, agencies, and governments, however. The benefits of an enterprise application are helpful, even essential, for individual developers and small organizations in an increasingly networked world.
The features that make enterprise applications powerful, like security and reliability, often make these applications complex. The Java EE platform is designed to reduce the complexity of enterprise application development by providing a development model, API, and runtime environment that allows developers to concentrate on functionality.
Tiered Applications
In a multi-tiered application, the functionality of the application is separated into isolated functional areas, called tiers. Typically, multi-tiered applications have a client tier, a middle tier, and a data tier (often called the enterprise information systems tier). The client tier consists of a client program that makes requests to the middle tier. The middle tier's business functions handle client requests and process application data, storing it in a permanent datastore in the data tier.
Java EE application development concentrates on the middle tier to make enterprise application management easier, more robust, and more secure.
The Client Tier
The client tier consists of application clients that access a Java EE server and that are usually located on a different machine from the server. The clients make requests to the server. The server processes the requests and returns a response back to the client. Many different types of applications can be Java EE clients, and they are not always, or even often Java applications. Clients can be a web browser, a stand-alone application, or other servers, and they run on a different machine from the Java EE server.
The Web Tier
The web tier consists of components that handle the interaction between clients and the business tier. Its primary tasks are the following:
Dynamically generate content in various formats for the client.
Collect input from users of the client interface and return appropriate results from the components in the business tier.
Control the flow of screens or pages on the client.
Maintain the state of data for a user's session.
Perform some basic logic and hold some data temporarily in JavaBeans components.
Java EE Technologies Used in the Web Tier
The following Java EE technologies are used in the web tier in Java EE applications.
Table 2-1 Web Tier Technologies
Technology |
Purpose |
|---|---|
Servlets |
Java programming language classes that dynamically process requests and construct responses, usually for HTML pages |
JavaServer Pages (JSP) |
Text-based documents that are compiled into servlets and define how dynamic content can be added to static pages, such as HTML pages. |
JavaServer Faces technology |
A user-interface component framework for web applications that allows you to include UI components (such as fields and buttons) on a page, convert and validate UI component data, save UI component data to server-side data stores, and maintain component state. |
JavaServer Pages Standard Tag Library |
A tag library that encapsulates core functionality common to JSP pages |
JavaBeans Components |
Objects that act as temporary data stores for the pages of an application |
The Business Tier
The business tier consists of components that provide the business logic for an application. Business logic is code that provides functionality to a particular business domain, like the financial industry, or an e-commerce site. In a properly designed enterprise application, the core functionality exists in the business tier components.
Java EE Technologies Used in the Business Tier
The following Java EE technologies are used in the business tier in Java EE applications:
Enterprise JavaBeans (enterprise bean) components
JAX-WS web service endpoints
Java Persistence API entities
The Enterprise Information Systems Tier
The enterprise information systems (EIS) tier consists of database servers, enterprise resource planning systems, and other legacy data sources, like mainframes. These resources typically are located on a separate machine than the Java EE server, and are accessed by components on the business tier.
Java EE Technologies Used in the EIS Tier
The following Java EE technologies are used to access the EIS tier in Java EE applications:
The Java Database Connectivity API (JDBC)
The Java Persistence API
The J2EE Connector Architecture
The Java Transaction API (JTA)