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.
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 standalone 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.