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Sun Java System Message Queue 3 2005Q4 Technical Overview 

Chapter 2
Client Programming Model

This chapter describes the basics of Message Queue client programming. It covers the following topics:

This chapter focuses on the design and implementation of Java clients. By and large, C client design roughly parallels Java client design. The final section of this chapter summarizes the differences between Java and C clients. For a detailed discussion of programming Message Queue clients, see Message Queue Developer’s Guide for Java Clients and Message Queue Developer’s Guide for C Clients.

Chapter 3, "Message Queue Service," explains how you can use the Message Queue service to support, manage, and tune messaging performance.

Design and Performance

The behavior of a Message Queue application depends on many factors: client design, connection configuration, broker configuration, broker tuning, and resource management. Some of these are the responsibility of the developer; others are the concern of the administrator. But in the best of possible worlds the developer should be aware of how the Message Queue service can support and scale the application design, and the administrator should be aware of the design goals when it comes time to tune the application. Messaging behavior can be optimized through redesign as well as through careful monitoring and tuning. Thus, a key aspect of creating a good Message Queue application is for the developer and the administrator to understand what can be realized at each stage of the application life cycle and to share information about desired and observed behavior.

Messaging Domains

Messaging middleware allows components and applications to communicate by producing and consuming messages. The JMS API defines two patterns or messaging domains that govern this communication: point-to-point messaging and publish/subscribe messaging. The JMS API is organized to support these patterns. The basic JMS objects: connections, sessions, producers, consumers, destinations, and messages are used to specify messaging behavior in both domains.

Point-To-Point Messaging

In the point-to-point domain, message producers are called senders and consumers are called receivers. They exchange messages by means of a destination called a queue: senders produce messages to a queue; receivers consume messages from a queue.

Figure 2-1 shows the simplest messaging operation in the point-to-point domain. MyQueueSender sends Msg1 to the queue destination MyQueue1. Then, MyQueueReceiver obtains the message from MyQueue1.

Figure 2-1  Simple Point-to-Point Messaging

Message travels from sender to receiver via a queue destination. Figure described in text.

Figure 2-2 shows a more complex picture of point-to-point messaging to illustrate the possibilities in this domain. Two senders, MyQSender1 and MyQSender2, use the same connection to send messages to MyQueue1. MyQSender3 uses an additional connection to send messages to MyQueue1. On the receiving side, MyQReceiver1 consumes messages from MyQueue1, and MyQReceiver2 and MyQReceiver3, share a connection in order to consume messages from MyQueue1.

Figure 2-2  Complex Point-to-Point Messaging

Figure shows two senders using one connection to send messages to one receiver. Also shows two consumers getting messages from same queue. Figure explained in text.

This more complex picture illustrates a number of additional points about point-to-point messaging.

The point-to-point model offers a number of advantages:

Publish/Subscribe Messaging

In the publish/subscribe domain, message producers are called publishers and message consumers are called subscribers. They exchange messages by means of a destination called a topic: publishers produce messages to a topic; subscribers subscribe to a topic and consume messages from a topic.

Figure 2-3 shows a simple messaging operation in the publish/subscribe domain. MyTopicPublisher publishes Msg1 to the destination MyTopic. Then, MyTopicSubscriber1 and MyTopicSubscriber2 each receive a copy of Msg1 from MyTopic.

Figure 2-3  Simple Publish/Subscribe Messaging

Figure shows one publisher sending the same message to two subscribers via a topic destination. Figure described in text.

While the publish/subscribe model does not require that there be more than one subscriber, two subscribers are shown in the figure to emphasize the fact that this domain allows you to broadcast messages. All subscribers to a topic get a copy of any message published to that topic.

Subscribers can be non-durable or durable. The broker retains messages for all active subscribers, but it only retains messages for inactive subscribers if these subscribers are durable.

Figure 2-4 shows a more complex picture of publish/subscribe messaging to illustrate the possibilities offered by this pattern. Several producers publish messages to the Topic1 destination. Several subscribers consume messages from the Topic1 destination. Unless, a subscriber is using a selector to filter messages, each subscriber gets all the messages published to the topic of choice. In Figure 2-4 MyTSubscriber2 has filtered out Msg2.

Figure 2-4  Complex Publish/Subscribe Messaging

Figure shows three publishers sending messages to three subscribers via one topic destination. Figure described in text.

This more complex picture illustrates a number of additional points about publish/subscribe messaging.

The main advantage of the publish/subscribe model is that it allows messages to be broadcast to subscribers.

Domain-Specific and Unified APIs

The JMS API defines interfaces and classes that you can use to implement either of the point-to-point or the publish/subscribe domains. These are the domain-specific API’s shown in columns 2 and 3 of Table 2-1. The JMS API defines an additional unified domain, which allows you to program a generic messaging client. The behavior of such a client is determined by the type of the destination to which it produces messages and from which it consumes messages. If the destination is a queue, messaging will behave according to the point-to-point pattern; if the destination is a topic; messaging will behave according to the publish/subscribe pattern.

Table 2-1  JMS Programming Domains and Objects 

Base Type
(Unified Domain)

Point-to-Point Domain

Publish/Subscribe Domain

Destination (Queue or Topic)1


















1Depending on programming approach, you must specify a particular destination type.

The unified domain was introduced with JMS version 1.1. If you need to conform to the earlier 1.02b specification, you can use the domain-specific API. Using the domain-specific API also provides a clean programming interface that prevents certain types of programming errors: for example, creating a durable subscriber for a queue destination. However, the domain-specific APIs have the disadvantage that you cannot combine point-to-point and publish/subscribe operations in the same transaction or in the same session. If you need to do that, you should choose the unified domain API. See The Request-Reply Pattern for an example of combining the two domains.

Programming Objects

The objects used to implement JMS messaging remain essentially the same across programming domains: connection factories connections, sessions, producers, consumers, messages, and destinations. These objects are shown in Figure 2-5. The figure shows, from the top down, how objects are derived, starting with the connection factory object.

Two of the objects, connection factories and destinations, are shown to reside in an object store. This is to underline the fact that these objects are normally created, configured, and managed as administered objects. We assume that connection factories and destinations are created administratively (rather than programmatically) throughout this chapter.

Figure 2-5  JMS Programming Objects

Figure shows relationship between connection factory, connection, session, producer, consumer, message, and destination. Figure described in text.

Table 2-2 summarizes the steps required to send and receive messages. Note that steps 1 and 3 through 6 are the same for senders and receivers.

Table 2-2  Producing and Consuming Messages.

Producing a Message

Consuming a Message

1. The administrator creates a connection factory administered object.

2. The administrator creates a physical destination and the administered object that refers to it.

3. The client obtains a connection factory object through a JNDI lookup.

4. The client obtains a destination object through a JNDI lookup.

5. The client creates a connection and sets any properties that are specific to this connection.

6. The client creates a session and sets the properties that govern messaging reliability.

7. The client creates a message producer

The client creates a message consumer

8. The client creates a message.

The client starts the connection.

9. The client sends a message.

The client receives a message.

The following sections describe the objects used by producers and consumers: connections, sessions, messages, and destinations. We will then complete the discussion of JMS objects by describing the production and consumption of messages.

Connection Factories and Connections

A client uses a connection factory object (ConnectionFactory) to create a connection. A connection object (Connection) represents a client’s active connection to the broker. It uses the underlying connection service that is either started by default or is explicitly started by the administrator for this client.

Both allocation of communication resources and authentication of the client take place when a connection is created. It is a relatively heavyweight object, and most clients do all their messaging with a single connection. Connections support concurrent use: any number of producers and consumers can share a connection.

When you create a connection factory, you can configure the behavior of all connections derived from it by setting its properties. For Message Queue, these specify the following information:

It is possible to override connection factory properties from the command line used to start the client application. It is also possible to override properties for any given connection by setting properties for that connection.

You can use a connection object to create session objects, to set up an exception listener, or to obtain JMS version and provider information.


If the connection represents a communication channel between the client and the broker, a session marks a single conversation between the client and the broker. Mainly, you use a session object to create messages, message producers, and message consumers. When you create a session, you configure reliable delivery through a number of acknowledgement options or through transactions. For more information, see Reliable Messaging.

According to the JMS specification, a session is a single-threaded context for producing and consuming messages. You can create multiple message producers and consumers for a single session, but you are restricted to using them serially. The threading implementation varies slightly for Java and C clients. Consult the appropriate developer’s guide for additional information about threading implementation and restrictions.

You can also use a session object to do the following:


A message is composed of three parts: a header, properties, and a body. You must understand this structure in order to compose a message properly and to configure certain messaging behaviors.

Message Header

A header is required of every JMS message. The header contains ten pre-defined fields, which are listed and described in Table 2-3.

Table 2-3  JMS-Defined Message Header 

Header Field



Specifies the name of the destination object to which the message is sent. (Set by the provider.)


Specifies whether the message is persistent. (Set by default by the provider or explicitly by the client for a producer or for an individual message.)


Specifies the time when the message will expire. (Set by default by the provider or by the client for a producer or for an individual message.)


Specifies the priority of the message within a 0 (low) to 9(high) range. (Set by default by the provider or set explicitly by the client for a producer or for an individual message.)


Specifies a unique ID for the message within the context of a provider installation. (Set by the provider.)


Specifies the time when the provider received the message. (Set by the provider.)


A value that allows a client to define a correspondence between two messages. (Set by the client if needed.)


Specifies a destination where the consumer should send a reply. (Set by the client if needed.)


A value that can be evaluated by a message selector. (Set by the client if needed.)


Specifies whether the message has already been delivered but not acknowledged. (Set by the provider.)

As you can see from reading through this table, message header fields serve a variety of purposes: identifying a message, configuring the routing of messages, providing information about message handling, and so on.

One of the most important fields, JMSDeliveryMode, determines the reliability of message delivery. This field indicates whether a message is persistent.

Some message header fields are set by the provider (either the broker or the client runtime) and others are set by the client. Message producers may need to configure header values to obtain certain messaging behaviors; message consumers may need to read header values in order to understand how the message was routed and what further processing it might need.

The header fields (JMSDeliveryMode, JMSExpiration, and JMSPriority) can be set at three different levels:

If these fields are set at more than one level, values set for the connection factory override those set for the individual message; values set for a given message override those set for the message’s producer.

Constant names for message header fields vary with the language implementation. See the Message Queue Developer’s Guide for Java Clients or the Message Queue Developer’s Guide for C Clients for more information.

Message Properties

A message can also include optional header fields, called properties, specified as property name and property value pairs. Properties allow clients and providers to extend the message header and can contain any information that the client or the provider finds useful to identify and process a message. Message properties allow a receiving client to ask that only those messages be delivered which fit a given criteria. For instance, a consuming client might indicate an interest for payroll messages concerning part-time employees located in New Jersey. The provider will not deliver messages that do not meet the specified criteria.

The JMS specification defines nine standard properties. Some of these are set by the client and some by the provider. Their names begin with the reserved characters “JMSX.” The client or the provider can use these properties to determine who sent a message, the state of the message, how often and when it was delivered. These properties are useful to the provider in routing messages and in providing diagnostic information.

Message Queue also defines message properties, these are used to identify compressed messages and how messages should be handled if they cannot be delivered. For more information see Message Queue Developer’s Guide for Java Clients.

Message Body

The message body contains the data that clients want to exchange.

The type of a JMS message determines what the body may contain and how it should be processed by the consumer, as specified in Table 2-4. The Session object includes a create method for each type of message body.

Table 2-4  Message Body Types 




A message whose body contains a stream of Java primitive values. It is filled and read sequentially.


A message whose body contains a set of name-value pairs. The order of entries is not defined.


A message whose body contains a Java string, for example an XML message.


A message whose body contains a serialized Java object.


A message whose body contains a stream of uninterpreted bytes.

Java clients can set a property to have the client runtime compress the body of a message being sent. The Message Queue runtime on the consumer side decompresses the message before delivering it.

Producing a Message

Messages are sent or published by a message producer, within the context of a connection and session. Producing a message is fairly straightforward: a client uses a message producer object (MessageProducer) to send messages to a physical destination, represented in the API by a destination object.

When you create the producer, you can specify a default destination that all the producer’s messages are sent to. You can also specify default values for the message header fields that govern persistence, priority, and time-to-live. These defaults are then used by all messages issuing from that producer unless you override them by specifying an alternate destination when sending the message or by setting alternate values for the header fields for a given message.

The message producer can also implement a request-reply pattern by setting the JMSReplyTo message header field. For more information, see The Request-Reply Pattern.

Consuming a Message

Messages are received by a message consumer, within the context of a connection and session. A client uses a message consumer object (MessageConsumer) to receive messages from a specified physical destination, represented in the API as a destination object.

Three factors affect how the broker delivers messages to a consumer:

The other major factor that affects message delivery and client design is the degree of reliability needed for the consumer. See Reliable Messaging.

Synchronous and Asynchronous Consumers

A message consumer can support either synchronous or asynchronous consumption of messages.

Using Selectors to Filter Messages

A message consumer can use a message selector to have the message service deliver only those messages whose properties match specific selection criteria. You specify this criteria when you create the consumer.

Selectors use an SQL-like syntax to match against message properties. For example,

color = ‘red’

size > 10

Java clients can also specify selectors when browsing a queue; this allows you to see which selected messages are waiting to be consumed.

Using Durable Subscribers

You can use a session object to create a durable subscriber to a topic. The broker retains messages for these kinds of subscribers even when the subscriber becomes inactive.

Because the broker must maintain state for the subscriber and resume delivery of messages when the subscriber is reactivated, the broker must be able to identify a given subscriber throughout its comings and goings. The subscriber’s identity is constructed from the ClientID property of the connection that created it and the subscriber name specified when you create the subscriber.

The Request-Reply Pattern

You can combine producers and consumers in the same connection (or even session when using the unified API). In addition, the JMS API allows you to implement a request-reply pattern for your messaging operations by using temporary destinations.

The message producer must do the following to set up the request-reply pattern:

  1. Create a temporary destination where the consumer can send replies.
  2. In the message to be sent, set the JMSReplyTo field of the message header to that temporary destination.

When the message consumer processes the message, it examines the JMSReplyTo field of the message to determine if a reply is required and sends the reply to the specified destination.

The request-reply mechanism saves the producer the trouble of setting up an administered object for the reply destination and makes it easy for the consumer to respond to the request. This pattern is useful when the producer must be sure that a request has been handled before proceeding.

Figure 2-6 illustrates a request/reply pattern that sends messages to a topic and receives replies in a temporary queue.

Figure 2-6  Request/Reply Pattern

Figure shows a publisher sending a message to two subscribers via a topic destination and receiving replies via a queue destination. Figure is explained in text.

As the figure shows, MyTopicPublisher produces Msg1 to the destination MyTopic. MyTopicSubsriber1 and MyTopicSubscriber2 receive the message and send a reply to MyTempQueue, from where MyTQReceiver retrieves it. This pattern might be useful for an application that published pricing information to a large number of clients and which queued their (reply) orders for sequential processing.

Temporary destinations last only as long as the connection that created them. Any producer can send to a temporary destination, but the only consumers that can access temporary destinations are those created by the same connection that created the destination.

Since the request/reply pattern depends on creating temporary destinations, you should not use this pattern in the following cases:

Reliable Messaging

Message delivery occurs in two hops: the first hop takes the message from the producer to a physical destination on the broker; the second hop takes the message from that destination to the consumer. Thus, a message can be lost in one of three ways: on its hop to the broker, while it’s in broker memory if the broker should happen to fail, and on its hop from the broker to the consumer. Reliable delivery guarantees that delivery will not fail at any of these stages. Because non-persistent messages can always be lost if the broker fails, reliable delivery only applies to persistent messages.

Two mechanisms are used to ensure reliable delivery:

The following sections describe these two aspects of ensuring reliability.


Acknowledgements are messages sent between the client and the message service to ensure reliable delivery of messages. Acknowledgements are used differently for producers and for consumers.

In the case of message production, the broker acknowledges that it has received the message, placed it in its destination and stored it persistently. The producer’s send() method blocks until it receives this acknowledgement. These acknowledgements are transparent to the client when persistent messages are sent.

In the case of message consumption, the client acknowledges that it has received delivery of a message from a destination and consumed it, before the broker can delete the message from that destination. JMS specifies different acknowledgement modes that represent different degrees of reliability.

For clients that are more concerned with performance than reliability, the Message Queue service extends the JMS API by providing a NO_ACKNOWLEDGE mode. In this mode, the broker does not track client acknowledgements, so there is no guarantee that a message has been successfully processed by the consuming client. Choosing this mode may give you better performance for non persistent messages that are sent to non-durable subscribers.


A transaction is a way of grouping the production and/or consumption of one or more messages into an atomic unit. The client and broker acknowledgement process described above applies, as well, to transactions. In this case, client runtime and broker acknowledgements operate implicitly on the level of the transaction. When a transaction commits, a broker acknowledgement is sent automatically.

A session can be configured as transacted, and the JMS API provides methods for initiating, committing, or rolling back a transaction.

As messages are produced or consumed within a transaction, the message service tracks the various sends and receives, completing these operations only when the JMS client issues a call to commit the transaction. If a particular send or receive operation within the transaction fails, an exception is raised. The client code can handle the exception by ignoring it, retrying the operation, or rolling back the entire transaction. When a transaction is committed, all its operations are completed. When a transaction is rolled back, all successful operations are cancelled.

The scope of a transaction is always a single session. That is, one or more producer or consumer operations performed in the context of a single session can be grouped into a single transaction. Since transactions span only a single session, you cannot have an end-to-end transaction encompassing both the production and consumption of a message.

The JMS specification also supports distributed transactions. That is, the production and consumption of messages can be part of a larger, distributed transaction that includes operations involving other resource managers, such as database systems. A transaction manager, like the one supplied by the Java Systems Application Server, must be available to support distributed transactions.

In distributed transactions, a distributed transaction manager tracks and manages operations performed by multiple resource managers (such as a message service and a database manager) using a two-phase commit protocol defined in the Java Transaction API (JTA), XA Resource API Specification. In the Java world, interaction between resource managers and a distributed transaction manager are described in the JTA specification.

Support for distributed transactions means that messaging clients can participate in distributed transactions through the XAResource interface defined by JTA. This interface defines a number of methods for implementing two-phase commit. While the API calls are made on the client side, the JMS message service tracks the various send and receive operations within the distributed transaction, tracks the transactional state, and completes the messaging operations only in coordination with a distributed transaction manager—provided by a Java Transaction Service (JTS).

As with local transactions, the client can handle exceptions by ignoring them, retrying operations, or rolling back an entire distributed transaction.

Persistent Storage

The other aspect of reliability is ensuring that the broker does not lose persistent messages before they are delivered to consumers. This means that when a message reaches its physical destination, the broker must place it in a persistent data store. If the broker goes down for any reason, it can recover the message later and deliver it to the appropriate consumers.

The broker must also persistently store durable subscriptions. Otherwise, in case of failure, it would not be able to deliver messages to durable subscribers who become active after a message has arrived in a topic destination.

Messaging applications that want to guarantee message delivery must specify messages as persistent and deliver them either to topic destinations with durable subscriptions or to queue destinations.

Chapter 3, "Message Queue Service," describes the default message store supplied by the Message Queue service and how an administrator can set up and configure an alternate store.

A Message’s Journey Through the System

By way of summarizing the material presented so far, this section describes how a message is delivered using the Message Queue service, from a producer to a consumer. In order to paint a complete picture, we need to add a further detail: The messages handled by the system in the course of delivery fall into two categories:

Message delivery is illustrated in Figure 2-7.

Figure 2-7  Message Delivery Steps

Diagram showing steps in the message delivery process in case of a persistent, reliably delivered message. Figure is described in text.

Message delivery steps for a persistent, reliably delivered message are as follows:

Message Production

1.   The client runtime delivers the message over the connection from the message producer to the broker.

Message Handling and Routing

2.   The broker reads the message from the connection and places it in the appropriate destination.

3.   The broker places the (persistent) message in the data store.

4.   The broker acknowledges receipt of the message to the client runtime of the message producer.

5.   The broker determines the routing for the message.

6.   The broker writes out the message from its destination to the appropriate connection, tagging it with a unique identifier for the consumer.

Message Consumption

7.   The message consumer’s client runtime delivers the message from the connection to the message consumer.

8.   The message consumer’s client runtime acknowledges consumption of the message to the broker.

Message End-of-Life

9.   The broker processes the client acknowledgement, and deletes the (persistent) message when all acknowledgements have been received.

10.   The broker confirms to the consumer’s client runtime that the client acknowledgement has been processed.

Working with SOAP Messages

SOAP (see SOAP Support for Java Clients) allows for the exchange of structured data (specified by an XML scheme) between two peers in a distributed environment. Sun’s implementation of SOAP does not currently support reliable SOAP messaging nor does it support publishing SOAP messages. However, you can use the Message Queue service to obtain reliable SOAP messaging and, if desired, to publish SOAP messages. The Message Queue service does not deliver SOAP messages directly, but it allows you to wrap SOAP messages into JMS messages, to produce and consume these messages like normal JMS messages, and to extract the SOAP message from the JMS message.

Message Queue provides SOAP support through two packages: javax.xml.messaging and com.sun.messaging.xml. You can use classes implemented in these libraries to receive a SOAP message, to wrap a SOAP message into a JMS message, and to extract a SOAP message from a JMS message. The J2EE platform provides the package java.xml.soap, which you can use to assemble and disassemble a SOAP message.

To obtain reliable SOAP messaging you need to do the following

  1. Use the objects defined in the java.xml.soap package to construct a SOAP message, or use the servlet defined in thejavax.xml.messaging package to receive a SOAP message, or use a web service like JAX-RPC to receive a SOAP message.
  2. Use the MessageTransformer utility to convert the SOAP message into a JMS message.
  3. Send the JMS message to the desired destination.
  4. Consume the JMS message asynchronously or synchronously.
  5. After the JMS message is consumed, use the MessageTransformer utility to convert it into a SOAP message.
  6. Use the SAAJ API (defined in the java.xml.soap package) to disassemble the SOAP message.

For detailed information about SOAP messages and their processing, see the Message Queue Developer’s Guide for Java Clients.

Java and C Clients

Message Queue provides a C API to its messaging services to enable legacy C applications and C++ applications to participate in JMS-based messaging.

The JMS programming model is the foundation for the design of a Message Queue C client. Message Queue Developer’s Guide for C Clients explains how this model is implemented by the C data types and functions.

Like the Java interface, the C interface supports the following features:

However, it is important to understand that the Java Message Service specification is a standard for Java clients only; thus the C Message Queue API is specific to the Message Queue provider and cannot be used with other JMS providers. A messaging application that includes a C client cannot be handled by another JMS provider.

The C interface, does not support the following features:

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Part No: 819-2574-10.   Copyright 2005 Sun Microsystems, Inc. All rights reserved.