Java 2004 — A Tour for the Midrange Developer


J2EE Overview


The J2EE Platform, Containers and Components

The J2EE specification defines a standard mechanism for hosting J2EE applications known as the J2EE platform. The platform uses a component-based approach to provide a multitiered, distributed, transactional model for enterprise applications. Conceptually, the architecture is almost always three tier — client, business logic, and database or Enterprise Information Systems (EIS). J2EE maintains control and provides services through interfaces or framework known as containers.

  • Server-side Containers
    • The server itself, which provides the J2EE runtime environment and the other two containers.
    • An EJB container to manage EJB components.
    • A Web container to manage servlets and JavaServer Pages.

  • Client-side Containers
    • An application container for standalone GUIs, console, and batch-type programs — the familiar Java applications started with the java command.
    • An applet container, meaning a browser, usually with the Java Plug-in.

In the server-side J2EE context, a component is a unit of functionality that is assembled, along with any required resources, into a J2EE application. Client-side containers communicate with the J2EE container and server-side components through a client JAR ( Java ARchive ) generated at deployment time.

  • Component Types
    • Client components, which correlate to the client containers.
    • Web components — servlets and JSPs.
    • EJB components.