B2B Integration : A Practical Guide to Collaborative E-commerce

Middleware Technologies 247
EJB technology has gained wide spread industry adoption and support.
The EJB specification is unique from CORBA and COM+ in that the
specification was developed using industry-wide collaboration, as with
CORBA, yet the specification is controlled by a single company, as
with COM+. This has given EJB the advantage of obtaining industry
acceptance from the application server vendors, while at the same time,
the ability to advance and modify the specification quickly, since
ultimately there is really only one owner and final decision-maker.
At a high level, EJBs do not differ much from CORBA, or even
COM+. EJBs require an IDL to separate the interface from implementation;
it supports transaction management, component level security and
messaging; and it is object-oriented based.
EJB differs from its brethren, as follows:
• EJB is a Java-based protocol. Though EJBs can interface with non-
Java components through wrappers or interfaces to CORBA, EJBs
are Java at heart.
• In addition to being platform independent, EJBs are also middleware
independent. An EJB application can, in theory, be ported from one
application server to another with minimal rework.
• EJBs live in a container. The container provides several services for
the EJBs, including lifecycle management and instance pooling and
transaction management. The container intercedes between client
calls on the remote interface and the corresponding methods in a
bean to enforce transaction and security constraints. The container
also enforces policies and restrictions on bean instances, such as
reentrance rules and security policies.
• EJBs were designed to wrap around, or encapsulate, existing legacy
systems, applications and datastores, allowing an organization to
leverage its existing infrastructure. These existing systems will appear
as a standard bean within the container. EJB can also co-exist with
other technologies, including COM/DCOM, ActiveX and CORBA.
Types of beans
The 'bean' part of Java Beans is Sun's name for a Java component.
There are two types of enterprise beans: session beans and entity beans.