J2EE tiers model
J2EE is a set of standards for developing and deploying enterprise Java applications, providing a multi-tier distributed application model, which can be divided basically into four main architectural tiers:
- Client tier
- Presentation tier
- Business logic tier
- The Enterprise Information Systems (EIS) tier
The client tier encompasses various client types, such as browsers, applets or stand-alone application clients. These clients can reside both within and outside of the enterprise firewall. User actions are translated into server requests and the server responses are translated into a user-readable format.
The presentation tier embraces Web components, either JSP or servlets, which are deployed on Web containers. They access data and services from other tiers, handle user requests and screen flow, and can also control user interaction, presenting the returned information back to the client.
Business logic components access enterprise data and business rules, consisting of enterprise beans, deployed on EJB containers. There are three kinds of enterprise beans: session beans, entity beans, and message-driven beans.
The Enterprise Information Systems tier is commonly referred to as the back-end tier; examples include database manager systems, mainframe transaction processing and other legacy systems.
J2EE does not specify the structure and implementation of the runtime. It introduces the concept of container; the contract between applications and the container is specified via the J2EE APIs. WAS V5.1 delivers the infrastructure for deploying J2EE-compliant applications, providing the appservers on which we will run our Java programs. The application server implements the Web container and EJB container components.
On a WebSphere topology, the basic components that interact to execute our application are:
- HTTP server and WebSphere Web server plug-in
- WebSphere Application Server Web and EJB containers
- Application databases
The Web container in IBM WAS V5.1 has an embedded HTTP transport, which allows for direct connection to the application without the need for a separate Web server. While use of this transport as a Web server is very useful for testing or development purposes it should not be used in production environments. For performance and security reasons, it is recommended that you use a standalone Web server and HTTP plug-in for the Web server in a production environment.
The emphasis of our topologies scenarios will be the mapping of the J2EE application architecture tiers to a physical deployment on WAS as well as how to apply different techniques and component associations in order to provide scalability, load balancing and failover, based on multiple criteria.
WebSphere is a trademark of the IBM Corporation in the United States, other countries, or both.
IBM is a trademark of the IBM Corporation in the United States, other countries, or both.