O'Reilly - Java Message Service

Java Message Service
IP multicast allows applications to join one or more IP multicast groups; each group uses
an IP network address that will redistribute any messages it receives to all members in its
group. In this way, applications can send messages to an IP multicast address and expect
the network layer to redistribute the messages appropriately (see Figure 1.3). Unlike a
centralized architecture, a distributed architecture doesn't require a server for the purposes
of routing messages - the network handles routing automatically. However, other serverlike
functionality is still required to be included with each client, such as message
persistence and message delivery semantics like once-and-only-once delivery.
1.1.3 Hybrid Architectures
Figure 1.3. Decentralized IP multicast architecture
A decentralized architecture usually implies that an IP multicast protocol is being used. A
centralized architecture usually implies that the TCP/IP protocol is the basis for
communication between the various components. A messaging vendor's architecture may
also combine the two approaches. Clients may connect to a daemon process using TCP/IP,
which in turn communicate with other daemon processes using IP multicast groups.
1.1.4 Centralized Architecture as a Model
Both ends of the decentralized and centralized architecture spectrum have their place in
enterprise messaging. The advantages and disadvantages of distributed versus centralized
architectures are discussed in more detail in Chapter 7. In the meantime we need a
common model for discussing other aspects of enterprise messaging. In order to simplify
discussions, this book uses a centralized architecture as a logical view of enterprise
messaging. This is for convenience only and is not an endorsement of centralized over
decentralized architectures. The term "message server" is frequently used in this book to
refer to the underlying architecture that is responsible for routing and distributing
messages. In centralized architectures, the message server is a middleware server or cluster
of servers. In decentralized architectures, the server refers to the local server-like facilities
of the client.
1.2 The Java Message Service (JMS)
The Java Message Service (JMS) is an API for enterprise messaging created by Sun
Microsystems. JMS is not a messaging system itself; it's an abstraction of the interfaces
and classes needed by messaging clients when communicating with messaging systems. In
the same way that JDBC abstracts access to relational databases and JNDI abstracts access
9