Multi-Tier Applications in Java

A multi-tier application is a distributed application that is hosted by different machines for creating enterprise applications. The functionality of the tier is divided into isolated functional areas and these functional areas are known as tiers. A multi-tier application consists the following four tiers:

1. Client tier: The client tier consists of a client program that makes requests to the middle tier. It consists of application clients that access a Java EE server and that are usually located on a different machine from the server. It performs the following tasks:
   1. The clients make requests to the server.
   2. 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.
2. Web tier: The web tier consists of components that handle the interaction between clients and the business tier. It performs the following tasks:
   1. Generates content in various formats for the client dynamically.
   2. Collects input from users of the client interface and returns appropriate results from the components in the business tier.
   3. Controls the flow of screens or pages on the client.
   4. Maintains the state of data for a user’s session.
   5. Performs some basic logic and holds some data temporarily in JavaBeans components.

   The following technologies can be used with the web tier:

   1. Servlets
   2. JavaServer Pages
   3. JavaServer Faces technology
   4. JavaServer Pages Standard Tag Library
   5. JavaBeans Components



3. Business tier: The business tier performs the following tasks:
   1. It provides 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.
   2. It provides the core functionality that exists in the business tier components.

   The following technologies can be used with the business tier:

   1. Enterprise JavaBeans (enterprise bean) components
   2. JAX-WS web service endpoints
   3. Java Persistence API entities
4. 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. This tier performs the following tasks:
   1. It handles enterprise information system software and includes enterprise infrastructure systems such as enterprise resource planning (ERP).
   2. It provides database connectivity for J2EE application components that might need access to enterprise information systems.

   The following technologies can be used with this tier:

   1. The Java Database Connectivity API (JDBC)
   2. The Java Persistence API
   3. The J2EE Connector Architecture
   4. The Java Transaction API (JTA)

• Previous Entry: Java Message Service
• Next Entry: What is the Favorite Folders Pane?