user manual

110 BES Developer’s Guide
EJB to CORBA mapping
There are a number of aspects to the relationship between CORBA and
Enterprise JavaBeans. Three important ones are the implementation of an
EJB container/server with an ORB, the integration of legacy systems into an
EJB middle tier, and the access of enterprise beans from non-Java
components, specifically clients. The EJB specification is currently only
concerned with the third aspect.
CORBA is a very suitable and natural platform on which to implement an EJB
infrastructure. CORBA addresses all of the concerns of the EJB specification
with the CORBA Core specification or the CORBA Services:
■
Support for distribution. CORBA Core and CORBA Naming Service
■
Support for transactions. CORBA Object Transaction Service
■
Support for security. CORBA Security Specification, including IIOP-over-
SSL
Additionally, CORBA allows the integration of non-Java components into an
application. These components can be legacy systems and applications, plus
different kinds of clients. Back-end systems can be easily integrated using
OTS and any programming language for which an IDL mapping exists. This
requires an EJB container to provide OTS and IIOP APIs.
The EJB specification is concerned with the accessibility of enterprise beans
from non-Java clients and provides an EJB to CORBA mapping. The goals of
the EJB/CORBA mapping are:
■
Supporting interoperability between clients written in any CORBA-
supported programming language and enterprise beans running on a
CORBA-based EJB server.
■
Enabling client programs to mix and match calls to CORBA objects and
enterprise beans within the same transaction.
■
Supporting distributed transactions involving multiple enterprise beans
running on CORBA-based EJB servers provided by different vendors.
The mapping is based on the Java-to-IDL mapping. The specification includes
the following parts: mapping of distribution-related aspects, the mapping of
naming conventions, the mapping of transactions, and the mapping of
security. We explain each of these aspects in the following sections. Since the
mapping uses new IDL features introduced by the OMG's Object-by-Value
specification, interoperability with other programming languages requires
CORBA 2.3-compliant ORBs.
Mapping for distribution
An enterprise bean has two interfaces that are remotely accessible: the
remote interface and the home interface. Applying the Java/IDL mapping to
these interfaces results in corresponding IDL specifications. The base classes
defined in the EJB specification are mapped to IDL in the same manner.