Integration Technologies - Guide to Cloud Computing for Business and Technology Managers - page 117

connecting APIs together on a point-to-point basis; consequently, it results in
a lot of integration points between applications.
5.4.2 Remote Method Invocation (RMI)
Traditional RPC systems are language neutral and therefore cannot provide
functionality that is not available on all possible target platforms. The Java
RMI provides a simple and direct model for distributed computation with
Java objects on the basis of the RPC mechanism. The Java RMI establishes
interobject communication. If the particular method happens to be on a
remote machine, Java provides the capability to make the RMI appear to
the programmer to be the same as if the method is on the local machine.
Thus, Java makes RMI transparent to the user. RMI applications comprise
two separate programs: a server and a client. RMI provides the mechanism
by which the server and the client communicate and pass information back
and forth.
There are two different kinds of classes that can be used in RMI: remote
and serializable classes. A remote object is an instance of a remote class. When
a remote object is used in the same address space, it can be treated just like
an ordinary object. But if it is used externally to the address space, the object
must be referenced by an object handle. Correspondingly, a serializable
object is an instance of a serializable class. A serializable object can be copied
from one address space to another. This means that a serializable object can
be a parameter or a return value. Note that if a remote object is returned, it is
the object handle being returned.
5.5 Messaging-Oriented Middleware (MOM)
Message-oriented middleware (MOM) is a client/server infrastructure that
enables and increases interoperability, flexibility, and portability of appli-
cations. It enables communication between applications over distributed
and heterogeneous platforms. It reduces complexity because it hides the
communication details and the details of platforms and protocols involved.
The functionality of MOM is accessed via APIs. It typically resides on both
ends, the client and the server side. It provides asynchronous communi-
cation and uses message queues to store the messages temporarily. The
applications can thus exchange messages without taking care of the details
of other applications, architectures, and platforms involved. The messages
can contain almost any type of data; asynchronous nature of communica-
tion enables the communication to continue even if the receiver is tempo-
rarily not available. The message waits in the queue and is delivered as
soon as the receiver is able to accept it. But asynchronous communication