web server - Borland Technical Publications

EJB to CORBA mapping
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.
For example, look at the IDL interface for an ATM enterprise session bean that has
methods to transfer funds between accounts and throws an insufficient funds
exception. By applying the Java/IDL mapping to the home and the remote interface,
you get the following IDL interface.
module transaction {
module ejb {
valuetype InsufficientFundsException : ::java::lang::Exception {};
exception InsufficientFundsEx {
::transaction::ejb::InsufficientFundsException value;
};
interface Atm : ::javax::ejb::EJBObject{
void transfer (in string arg0, in string arg1, in float arg2)
raises (::transaction::ejb::InsufficientFundsEx);
};
interface AtmHome : ::javax::ejb::EJBHome {
::transaction::ejb::Atm create ()
raises (::javax::ejb::CreateEx);
};
};};};};
Mapping for naming
A CORBA-based EJB runtime environment that wants to enable any CORBA clients to
access enterprise beans must use the CORBA Naming Service for publishing and
resolving the home interfaces of the enterprise beans. The runtime can use the
CORBA Naming Service directly or indirectly via JNDI and its standard mapping to the
CORBA Naming Service.
JNDI names have a string representation of the following form “directory1/directory2/
.../directoryN/objectName”. The CORBA Naming Service defines names as a
sequence of name components.
typedef string Istring;
struct NameComponent {
Istring id;
Istring kind;
};
typedef sequence Name;
Each “/” separated name of a JNDI string name is mapped to a name component; the
leftmost component is the first entry in the CORBA Naming Service name.
A JNDI string name is relative to some naming context, which calls the JNDI root
context. The JNDI root context corresponds to a CORBA Naming Service initial
context. CORBA Naming Service names are relative to the CORBA initial context.
Chapter 11: Writing enterprise bean clients 93