J2EE is an environment for developing and deploying enterprise applications. The J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing multitiered, web-based applications.
A J2EE module consists of one or more J2EE components for the same container type and one component deployment descriptor of that type.
1. Application client module
2. Web module
3. Enterprise JavaBeans module
4. Resource adapter module
The web module contains:
--class files for servlets,
--GIF and HTML files, and
--a Web deployment descriptor.
Web modules are packaged as JAR files with a .war (Web ARchive) extension.
The Session bean and Entity bean are two main parts of EJB container.
--represents a workflow on behalf of a client
--one-to-one logical mapping to a client.
--created and destroyed by a client
--not permanent objects
--lives its EJB container(generally) does not survive system shut down
--two types: stateless and stateful beans
--represents persistent data and behavior of this data
--can be shared among multiple clients
--persists across multiple invocations
--findable permanent objects
--outlives its EJB container, survives system shutdown
--two types: container managed persistence(CMP) and bean managed persistence(BMP)
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