Messaging in Java
24.04.2012
Agenda
Enterprise Application Integration
Messaging Overview
JMS Architecture
DEMO(s)
1. Instant Messaging
Enterprise Application Integration
Integration Challenge
Systems that need to be linked together very often: - reside on different operating systems
- use different database solutions and different
computer languages
Enterprise Application Integration
EAI definition, by Gartner Group
„Unrestricted sharing of data and business processes
among any connected application or data sources in the enterprise.”
Messaging plays a key role in heterogeneous integration
What’s messaging?
• Messaging approach will mean that two or more
applications will exchange information in the form of messages.
• A message is a self-contained package of business data and network routing headers.
• The business data contained in a message can be anything - usually contains information about some business transaction.
Messaging advantages
• Heterogeneous Integration • Reduce System Bottlenecks • Increase Scalability
Message-Oriented Middleware
• Allows two or more applications to exchange information in the form of messages
• Provides a mechanism for integrating applications in a loosely coupled, flexible manner.
• Provide asynchronous delivery of data between applications on a
store and forward basis. The applications do not communicate
directly with each other, but instead communicate with the MOM, which acts as an intermediary.
• Provides assured delivery of messages and relieves application programmers from knowing the details of remote procedure calls (RPC) and networking/communications protocols.
• Usually provide fault tolerance, load balancing, scalability, and transactional support for enterprises that need to reliably
Centralized architecture
Typically, a centralized architecture uses a
hub-and-spoke topology.
Message Oriented Middleware Vendors
• Open Source
• Apache ActiveMQ
• Glassfish Open Message Queue
• Object Web JORAM
• Commercial
• BEA Systems MessageQ
• IBM MQSeries
• TIBCO Rendezvous Software Bus
• Progress SonicMQ
Messaging c.d.
• Applications exchange messages through virtual channels called destinations.
• Message being sent is addressed to a destination not a specific application.
• Any application that subscribes or registers an interest in that destination may receive the message
Messaging Models
1. Point to Point
Point to Point
• Allows JMS clients to send and receive messages both
synchronously and asynchronously via virtual channels
known as queues.
• Message producers are called senders and message consumers are called receivers.
• Messages sent to a queue are received by one and only
one receiver, even though there may be many receivers
Point to Point
• Point-to-point messaging supports asynchronous “fire
and forget” messaging as well as synchronous request/reply messaging.
• The point-to-point model supports load balancing, which allows multiple receivers to listen on the same queue, therefore distributing the load.
• JMS provider takes care of managing the queue,
ensuring that each message is consumed once and only
once by the next available receiver in the group.
• Point-to-point also offers other features, such as a
queue browser that allows a client to view the contents
Publish and Subscribe
• Messages are published to a virtual channel called a
topic.
• Message producers are called publishers, whereas message consumers are called subscribers.
• Messages published to a topic using the
publish-and-subscribe model can be received by multiple subscribers
Publish and Subscribe
• The pub/sub model tends to be more decoupled than the p2p model in that the message publisher is
generally unaware of how many subscribers there are or what those subscribers do with the message.
• Nondurable subscribers are temporary subscriptions
that receive messages only when they are actively listening on the topic.
• Durable subscribers will receive a copy of every
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What is MQ?
•Most large organizations today have IT systems from various
manufacturers.... makes it difficult to share communications and data across systems.
•These organizations need to communicate and share data with suppliers and customers, who might also have disparate systems.
•Handy to have a messaging tool that could receive data from one type of system and send that data to another type.
•WebSphere MQ facilitates application integration by passing messages between applications and web services.
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What is MQ?
•Message queues, and the software that manages them enable program-to-program communication.
•Messaging and Queuing an be understood as follows:
• Messaging means that programs communicate by sending each other
messages (data) rather than by calling each other.
• Queuing means messages are placed on queues in storage,
•Programs can run independently of each other, at different speeds and times,in different locations, and without having a logical connection
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Synchronous Communication
•Program A prepares a message and puts it on Queue 1.
•Program B gets the message from Queue 1 and processes it.
•Both Program A and Program B use an application programming interface (API) to put messages on a queue and get messages from a queue.
•The MQ API is called the Message Queue Interface (MQI).
•When Program A puts a message on Queue 1, Program B might not be running. The queue stores the message safely until Program B starts and is ready to get the message.
•When Program B gets the message from Queue1, Program A might no longer be running. For this model, there is no requirement for two
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Asynchronous Communication
•Using the asynchronous model, Program A puts messages on Queue 1 for Program B to process
•Program B sends the responses to Queue 2
•It is Program C, acting asynchronously to Program A, gets the replies from Queue 2 and processes them.
What is JMS?
The Java Message Service specification 1.1 states:
“JMS is a set of interfaces and associated semantics that define how a JMS client accesses the facilities of an
Java Message Service c.d.
• JMS provides a standard, portable way for Java programs to send and receive messages through a MOM product
• Programs written with JMS can run on any MOM that implements the JMS standard.
• Portability - JMS API is provided by Oracle as a set of interfaces, MOM providers implement these interfaces. • As a developer, you build a JMS application by defining
JMS Objectives
• Define a common set of messaging concepts and facilities.
• Minimize the concepts a programmer must learn to use enterprise messaging.
• Maximize the portability of messaging applications. • Minimize the work needed to implement a provider. • Provide client interfaces for both point-to-point and
What JMS does not provide
JMS providers are free to implement these features in any manner they please, if at all:
•Load balancing and fault tolerance
•Error and advisory system messages and notification •Administration
•Security
•Wire protocol
JMS Application Components
• JMS clients. Java programs that send and receive
messages using the JMS API.
• Messages. The format and content of messages to be
exchanged by JMS and non-JMS clients is integral to the design of a JMS application.
• JMS provider. Supplied concrete implementations of
JMS interfaces specific to given MOM product.
• Administered objects. An administrator of a
Administered Objects
• JMS Portability – objects that implement the JMS
interfaces must be isolated from a provider’s proprietary technologies (which is achieved by
administered objects).
• Administered Objects that implement JMS interfaces,
Administered Objects c.d.
There are two types of administered objects:
•ConnectionFactory: Used to create a connection to the
provider's underlying messaging system.
•Destination: Used by the JMS client to specify the
destination of messages being sent or the source of messages being received.
Message
Message is divided into three constituent parts:
• The header is a standard set of fields that are used by both clients andvproviders to identify and route messages. • Properties provide a facility for adding optional header fields to a message.
• The body of the message contains the content to be delivered to a receiving application. Each message
Message types
• StreamMessage: Contains a stream of Java primitive values that are filled and read sequentially using standard stream operations.
• MapMessage: Contains a set of name-value pairs; the names are of type string and the values are Java
primitives.
• TextMessage: Contains a String.
JMS Interfaces
JMS Common Interface Peer to Peer Publish and Subscribe
ConnectionFactory QueueConnectionFactory TopicConnectionFactory
Connection QueueConnection TopicConnection
Destination Queue Topic
Session QueueSession TopicSession
MessageProducer QueueSender TopicPublisher
MessageConsumer QueueReceiver,
JMS Interfaces
ConnectionFactory
ConnectionFactory is an administered object that is
retrieved from JNDI to create a connection to a provider. It contains a createConnection() method, which
JMS Interfaces
Connection
Connection encapsulates an active connection to a provider. Methods:
•createSession(boolean, int): Returns a Session object. The
boolean parameter indicates whether the Session is transacted or not; the int indicates the acknowledgment mode.
•start(): Activates the delivery of messages from the provider.
•stop(): Temporarily stops delivery of messages; delivery can be
restarted with start().
•close(): Closes the connection to the provider and releases
JMS Interfaces
Session
Session is the single-threaded context for sending and receiving messages. Methods:
• createProducer(Destination): Returns a MessageProducer
object to send messages to the specified Destination.
• createConsumer(Destination): Returns a MessageConsumer
object to receive messages from the specified Destination.
• commit(): Commits all consumed or produced messages for the current
transaction.
• rollback(): Rolls back all consumed or produced messages for the
current transaction.
• create<MessageType>Message(...): A variety of methods that
JMS Interfaces
Destination
JMS Interfaces
MessageProducer
MessageProducer is used to send messages. Methods:
• send(Message): Sends the indicated Message.
• setDeliveryMode(int): Sets the delivery mode for
subsequent messages sent; valid values are
DeliveryMode.PERSISTENT and DeliveryMode.NON_PERSISTENT.
• setPriority(int): Sets the priority for subsequent
messages sent; valid values are 0 through 9.
• setTimeToLive(long): Sets the duration before
JMS Interfaces
MessageConsumer
MessageConsumer is used to receive messages. Methods:
• receive(): Returns the next message that arrives; this
method blocks until a message is available.
• setMessageListener(MessageListener): Sets the
JMS Interfaces
MessageListener
MessageListener is an interface with a single method -- onMessage(Message) -- that provides asynchronous receipt and processing of messages.
This interface should be implemented by a client class and an instance of that class passed to the MessageConsumer object with the setMessageListener(MessageListener)
Developing JMS Client
1. Look up a ConnectionFactory through JNDI.
2. Look up one or more Destination s through JNDI. 3. Use the ConnectionFactory to create a Connection. 4. Use the Connection to create one or more Session’s. 5. Use a Session and a Destination to create the required
MessageProducer’s and MessageConsumer’s.
Simple scenario – MessageSender
Simple scenario – MessageSender
2. Create required JMS objects
Simple scenario – MessageReceiver
Simple scenario – MessageReceiver
2. Implement receiver interface.
REFERENCES
• Java Message Service, 2nd edition, Mark Richards, Richard Monson-Haefel, and David A. Chappell by O’Reilly
• Introducing the Java Message Service, Willy Farrell by
IBM
