J2EE platform technologies
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J2EE platform technologies
The J2EE platform specifies technologies to support multitier enterprise applications.
These technologies fall into the following three categories:
•
Components
Developers use component technologies to create the essential parts
of an enterprise application: the user interface and the business logic. You develop
components as reusable modules that you can share among multiple enterprise
applications.
•
Containers
Containers provide application components with J2EE system-level
services. Containers let you customize components to use the resources available in
the environment in which they are deployed.
•
Communication
Since most enterprise applications require access to existing
resources, the J2EE platform supports APIs that provide access to database,
transaction, naming and directory, messaging services, and legacy applications. The
J2EE platform also provides technologies that enable communication between clients
and servers and between collaborating objects hosted by different servers.
Components
A J2EE component is a self-contained functional software unit that is assembled into a
J2EE application with its related classes and files and communicates with other
components.
The J2EE platform supports the following types of components:
Containers
Before a component can be executed, it must be assembled into a J2EE application and
deployed into its container. Containers are standardized runtime environments that
provide specific component services, such as life cycle management, security,
deployment, and runtime services. Each type of container (EJB, web, JSP, servlet, applet,
and application client) also provides component-specific services.
The assembly process involves specifying container settings for each component in the
J2EE application and for the application itself. Container settings customize the
underlying support provided by the J2EE server, including services such as security
checks, transaction management, Java Naming and Directory Interface (JNDI) lookups,
and remote connectivity. You specify application behavior at assembly or deployment
time with deployment descriptors.
Deployment descriptors
are text files that specify
component behavior in terms of well-defined XML tags.
Component
Includes
Client
Web browsers, applets, and applications (optionally JavaBeans, but
not considered a J2EE component)
Web
Java Servlets, JSPs, (optionally JavaBeans, but not considered a
J2EE component)
Business
EJBs (session, entity, and message-driven beans)
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