2 Understanding WebLogic JMS

These sections briefly review the different Java Message Service (JMS) concepts and features, and describe how they work with other application objects and WebLogic Server.

It is assumed the reader is familiar with Java programming and JMS 1.1 concepts and features.

Overview of the Java Message Service and WebLogic JMS
Understanding the Messaging Models
Value-Added Public JMS API Extensions
Understanding the JMS API

Overview of the Java Message Service and WebLogic JMS

WebLogic JMS is an enterprise-class messaging system that is tightly integrated into the WebLogic Server platform. It fully supports the JMS Specification, described at http://java.sun.com/products/jms/docs.html, and also provides numerous "WebLogic JMS Extensions" that go above and beyond the standard JMS APIs.

What Is the Java Message Service?

An enterprise messaging system enables applications to communicate with one another through the exchange of messages. A message is a request, report, and/or event that contains information needed to coordinate communication between different applications. A message provides a level of abstraction, allowing you to separate the details about the destination system from the application code.

The Java Message Service (JMS) is a standard API for accessing enterprise messaging systems. Specifically, JMS:

Enables Java applications sharing a messaging system to exchange messages
Simplifies application development by providing a standard interface for creating, sending, and receiving messages

The following figure illustrates WebLogic JMS messaging.

Figure 2-1 WebLogic JMS Messaging

Description of "Figure 2-1 WebLogic JMS Messaging"

As illustrated in the figure, WebLogic JMS accepts messages from producer applications and delivers them to consumer applications.

Implementation of Java Specifications

WebLogic Server is compliant with the following Java specifications.

Java EE Specification

WebLogic Server is compliant with the Java Platform, Enterprise Edition (Java EE) Version 5.0 specification, described at http://java.sun.com/javaee/5/docs/api/.

JMS Specification

WebLogic Server is fully compliant with the JMS 1.1 Specification, at http://java.sun.com/products/jms/docs.html, and can be used in production.

WebLogic JMS Architecture

The following figure illustrates the WebLogic JMS architecture.

Figure 2-2 WebLogic JMS Architecture

Description of "Figure 2-2 WebLogic JMS Architecture"

Major Components

The major components of the WebLogic JMS Server architecture, as illustrated in Figure 2-2, include:

JMS servers that can host a defined set of modules and any associated persistent storage that reside on a WebLogic Server instance.
JMS modules contains configuration resources (such as queues, topics, and connections factories) and are defined by XML documents that conform to the http://xmlns.oracle.com/weblogic/weblogic-jms/1.0/weblogic-jms.xsd schema.
Client JMS applications that either produce messages to destinations or consume messages from destinations.
JNDI (Java Naming and Directory Interface), which provides a resource lookup facility. JMS resources such as connection factories and destinations are configured with a JNDI name. The runtime implementations of these resources are then bound into JNDI using the given names.
WebLogic persistent storage (file store or JDBC-accessible) for storing persistent message data.

Understanding the Messaging Models

JMS supports two messaging models: point-to-point (PTP) and publish/subscribe (pub/sub). The messaging models are very similar, except for the following differences:

PTP messaging model enables the delivery of a message to exactly one recipient.
Pub/sub messaging model enables the delivery of a message to multiple recipients.

Each model is implemented with classes that extend common base classes. For example, the PTP class javax.jms.Queue (described at http://java.sun.com/javaee/5/docs/api/javax/jms/Queue.html) and the pub/sub class javax.jms.Topic (described at http://java.sun.com/javaee/5/docs/api/javax/jms/Topic.html) both extend the class javax.jms.Destination (described at http://java.sun.com/javaee/5/docs/api/javax/jms/Destination.html).

Each message model is described in detail in the following sections.

Note:

The terms producer and consumer are used as generic descriptions of applications that send and receive messages, respectively, in either messaging model. For each specific messaging model, however, unique terms specific to that model are used when referring to producers and consumers.

Point-to-Point Messaging

The point-to-point (PTP) messaging model enables one application to send a message to another. PTP messaging applications send and receive messages using named queues. A queue sender (producer) sends a message to a specific queue. A queue receiver (consumer) receives messages from a specific queue.

The following figure illustrates PTP messaging.

Figure 2-3 Point-to-Point (PTP) Messaging

Description of "Figure 2-3 Point-to-Point (PTP) Messaging"

Multiple queue senders and queue receivers can be associated with a single queue, but an individual message can be delivered to only one queue receiver.

If multiple queue receivers are listening for messages on a queue, WebLogic JMS determines which one will receive the next message on a first come, first serve basis. If no queue receivers are listening on the queue, messages remain in the queue until a queue receiver attaches to the queue.

Publish/Subscribe Messaging

The publish/subscribe (pub/sub) messaging model enables an application to send a message to multiple applications. Pub/sub messaging applications send and receive messages by subscribing to a topic. A topic publisher (producer) sends messages to a specific topic. A topic subscriber (consumer) retrieves messages from a specific topic.

The following figure illustrates pub/sub messaging.

Figure 2-4 Publish/Subscribe (Pub/Sub) Messaging

Description of "Figure 2-4 Publish/Subscribe (Pub/Sub) Messaging"

Unlike with the PTP messaging model, the pub/sub messaging model allows multiple topic subscribers to receive the same message. JMS retains the message until all topic subscribers have received it.

The Pub/Sub messaging model supports durable subscribers, allowing you to assign a name to a topic subscriber and associate it with a user or application. For more information about durable subscribers, see Setting Up Durable Subscriptions.

Message Persistence

As per the "Message Delivery Mode" section of the JMS Specification, described at http://java.sun.com/products/jms/docs.html, messages can be specified as persistent or non-persistent:

A persistent message is guaranteed to be delivered once-and-only-once. The message cannot be lost due to a JMS provider failure and it must not be delivered twice. It is not considered sent until it has been safely written to a file or database. WebLogic JMS writes persistent messages to a WebLogic persistent store (disk-base file or JDBC-accessible database) that is optionally targeted by each JMS server during configuration.
Non-persistent messages are not stored. They are guaranteed to be delivered at-most-once, unless there is a JMS provider failure, in which case messages may be lost, and must not be delivered twice. If a connection is closed or recovered, all non-persistent messages that have not yet been acknowledged will be redelivered. Once a non-persistent message is acknowledged, it will not be redelivered.

For information about using the system-wide, WebLogic Persistent Store, see "Using the WebLogic Persistent Store" in Configuring Server Environments for Oracle WebLogic Server.

Value-Added Public JMS API Extensions

WebLogic JMS is tightly integrated into the WebLogic Server platform, allowing you to build highly-secure Java EE applications that can be easily monitored and administered through the WebLogic Server console. In addition to fully supporting XA transactions, WebLogic JMS also features high availability through its clustering and service migration features, while also providing seamless interoperability with other versions of WebLogic Server and third-party messaging providers.

For a detailed listing of these value-added features, see "WebLogic Server Value-Added JMS Features" in Configuring and Managing JMS for Oracle WebLogic Server.

WebLogic Server Value-Added JMS Features

In addition to the standard JMS APIs specified by the JMS Specification, WebLogic Server provides numerous weblogic.jms.extensions APIs, which includes the classes and methods described in the following table.

Table 2-1 WebLogic JMS Public API Extensions

Interface/Class	Function
ConsumerInfo, DestinationInfo	Provides consumer and destination information to management clients in CompositeData format.
JMSMessageFactoryImpl, WLMessageFactory	Provides a factory and methods to: Create JMS messages Create JMS bytes messages Create JMS map messages Creating JMS object messages Creating JMS stream messages Creating JMS text messages Creating JMS XML messages
JMSMessageInfo	Provide browsing and message manipulation using JMX.
JMSModuleHelper, JMSNamedEntityModifier	Monitors JMS runtime MBeans and manages JMS Module configuration entities in a JMS module.
JMSRuntimeHelper	Monitors JMS runtime JMX MBeans.
MDBTransaction	Associates a message delivered to a MDB (message-driven bean) with a transaction.
WLDestination	Determines if a destination is a queue or a topic.
WLMessage	Sets a delivery time for messages, redelivery limits, and send timeouts.
WLMessageProducer	Sets a message delivery times for producers and Unit-of-Order names.
WLQueueSession, WLSession, WLTopicSession	Provides additional fields and methods that are not supported by `javax.jms.QueueSession`, `javax.jms.Session`, and `javax.jms.TopicSession`.
XMLMessage	Creates XML messages.
Schedule	Sets a scheduled delivery times for messages.
JMSHelper	Monitors JMS runtime MBeans. Deprecated in this release of WebLogic Server. Replaced by JMSModuleHelper.
ServerSessionPoolFactory, ServerSessionPoolListener	Provides interfaces for creating server session pools and message listeners. Note: Session pool configuration objects are deprecated for this release of WebLogic Server. They are not a required part of the Java EE specification, do not support JTA user transactions, and are largely superseded by message-driven beans (MDBs), which are a required part of Java EE. For more information on designing MDBs, see Programming Message-Driven Beans for Oracle WebLogic Server.

This API also supports NO_ACKNOWLEDGE and MULTICAST_NO_ACKNOWLEDGE acknowledge modes, and extended exceptions, including throwing an exception:

To the session exception listener (if set), when one of its consumers has been closed by the server as a result of a server failure, or administrative intervention.
From a multicast session when the number of messages received by the session, but not yet delivered to the message listener, exceeds the maximum number of messages allowed for that session.
From a multicast consumer when it detects a sequence gap (message received out of sequence) in the data stream.

Understanding the JMS API

To create a JMS applications, use the javax.jms API at http://java.sun.com/javaee/5/docs/api/javax/jms/package-summary.html. The API allows you to create the class objects necessary to connect to the JMS, and send and receive messages. JMS class interfaces are created as subclasses to provide queue- and topic-specific versions of the common parent classes.

The following table lists the JMS classes described in more detail in subsequent sections. For a complete description of all JMS classes, see the javax.jms, at http://java.sun.com/javaee/5/docs/api/javax/jms/package-summary.html, or the weblogic.jms.extensions Javadoc.

Table 2-2 WebLogic JMS Classes

JMS Class	Description
ConnectionFactory	Encapsulates connection configuration information. A connection factory is used to create connections. You look up a connection factory using JNDI.
Connection	Represents an open communication channel to the messaging system. A connection is used to create sessions.
Session	Defines a serial order for the messages produced and consumed.
Destination	Identifies a queue or topic, encapsulating the address of a specific provider. Queue and topic destinations manage the messages delivered from the PTP and pub/sub messaging models, respectively.
MessageProducer and MessageConsumer	Provides the interface for sending and receiving messages. Message producers send messages to a queue or topic. Message consumers receive messages from a queue or topic.
Message	Encapsulates information to be sent or received.
ServerSessionPoolFactory ^Foot 1	Encapsulates configuration information for a server-managed pool of message consumers. The server session pool factory is used to create server session pools.
ServerSessionPool ^Foot 2	Provides a pool of server sessions that can be used to process messages concurrently for connection consumers.
ServerSession ^Foot 3	Associates a thread with a JMS session.
ConnectionConsumer ^Foot 4	Specifies a consumer that retrieves server sessions to process messages concurrently.

^Footnote 1Supports an optional JMS interface for processing multiple messages concurrently.

^Footnote 2Supports an optional JMS interface for processing multiple messages concurrently.

^Footnote 3Supports an optional JMS interface for processing multiple messages concurrently.

^Footnote 4Supports an optional JMS interface for processing multiple messages concurrently.

For information about configuring JMS resources, see "Configuring Basic JMS System Resources" in Configuring and Managing JMS for Oracle WebLogic Server. The procedure for setting up a JMS application is presented in Setting Up a JMS Application.

ConnectionFactory

A ConnectionFactory encapsulates connection configuration information, and enables JMS applications to create a Connection (see Connection). A connection factory supports concurrent use, enabling multiple threads to access the object simultaneously. You can use the preconfigured default connection factories provided by WebLogic JMS, or you can configure one or more connection factories to create connections with predefined attributes that suit your application.

Using the Default Connection Factories

WebLogic JMS defines two default connection factories, which you can look up using the following JNDI names:

weblogic.jms.ConnectionFactory
weblogic.jms.XAConnectionFactory

You only need to create a user-defined a connection factory if the settings of the default factories are not suitable for your application. The main difference between the preconfigured settings for the default connection factories is the default value for the "XA Connection Factory Enabled" attribute which is used to enable JTA transactions, as shown in the following table.

Table 2-3 XA Transaction(al) Settings for Default Connection Factories

Default Connection Factory. . .	XA Connection Factory Enabled setting is. . .
weblogic.jms.ConnectionFactory	False
weblogic.jms.XAConnectionFactory	True

An XA factory is required for JMS applications to use JTA user-transactions, but is not required for transacted sessions. For more information about using transactions with WebLogic JMS, see Chapter 12, "Using Transactions with WebLogic JMS."

All other default factory configuration attributes are set to the same default values as a user-defined connection factory.

For more information about the XA Connection Factory Enabled attribute, and to see the default values for the other connection factory attributes, see "JMS Connection Factory: Configuration: Transactions" in the Oracle WebLogic Server Administration Console Help.

Another distinction when using the default connection factories is that you have no control over targeting the WebLogic Server instances where the connection factory may be deployed. However, you can disable the default connection factories on a per-server basis.

For more information on enabling or disabling the default connection factories, see "Servers: Configuration: Services" in the Oracle WebLogic Server Administration Console Help.

To deploy a connection factory on specific independent servers, on specific servers within a cluster, or on an entire cluster, you must configure a new connection factory and specify the appropriate target, as explained in "Connection Factory Configuration" in Configuring and Managing JMS for Oracle WebLogic Server.

Note:

For backwards compatibility, WebLogic JMS still supports two deprecated default connection factories. The JNDI names for these factories are: javax.jms.QueueConnectionFactory and javax.jms.TopicConnectionFactory.

Configuring and Deploying Connection Factories

A system administrator can define and configure one or more connection factories to create connections with predefined attributes and WebLogic Server will add them to the JNDI space during startup. The application then retrieves a connection factory using WebLogic JNDI. Any user-defined connection factories must be uniquely named.

For information on configuring connection factories, see "Configure connection factories" in the Oracle WebLogic Server Administration Console Help.

A system administrator establishes cluster-wide, transparent access to JMS destinations from any server in the cluster by targeting to the cluster or by targeting to one or more server instances in the cluster. This way, each connection factory can be deployed on multiple WebLogic Server instances. For more information on JMS clustering, refer to "Configuring Advanced WebLogic JMS Resources" in Configuring and Managing JMS for Oracle WebLogic Server.

The ConnectionFactory Class

The ConnectionFactory class does not define methods; however, its subclasses define methods for the respective messaging models. A connection factory supports concurrent use, enabling multiple threads to access the object simultaneously.

Note:

For this release, you can use the JMS Version 1.1 specification connection factories or you can choose to use the subclasses.

The following table describes the ConnectionFactory subclasses.

Table 2-4 ConnectionFactory Subclasses

Subclass. . .	In Messaging Model. . .	Is Used to Create. . .
QueueConnectionFactory	PTP	`QueueConnection` to a JMS PTP provider.
TopicConnectionFactory	Pub/Sub	`TopicConnection` to a JMS Pub/Sub provider.

To learn how to use the ConnectionFactory class within an application, see Chapter 5, "Developing a Basic JMS Application," or the javax.jms.ConnectionFactory Javadoc at http://java.sun.com/javaee/5/docs/api/javax/jms/ConnectionFactory.html.

Connection

A Connection represents an open communication channel between an application and the messaging system, and is used to create a Session (see Session) for producing and consuming messages. A connection creates server-side and client-side objects that manage the messaging activity between an application and JMS. A connection may also provide user authentication.

A Connection is created by a ConnectionFactory (see ConnectionFactory), obtained through a JNDI lookup.

Due to the resource overhead associated with authenticating users and setting up communications, most applications establish a single connection for all messaging. In the WebLogic Server, JMS traffic is multiplexed with other WebLogic services on the client connection to the server. No additional TCP/IP connections are created for JMS. Servlets and other server-side objects may also obtain JMS Connections.

By default, a connection is created in stopped mode. For information about how and when to start a stopped connection, see Starting, Stopping, and Closing a Connection.

Connections support concurrent use, enabling multiple threads to access the object simultaneously.

Note:

For this release, you can use the JMS Version 1.1 specification connection objects or you can choose to use the subclasses.

The following table describes the Connection subclasses.

Table 2-5 Connection Subclasses

Subclass. . .	In Messaging Model. . .	Is Used to Create. . .
QueueConnection	PTP	`QueueSessions`, and consists of a connection to a JMS PTP provider created by `QueueConnectionFactory`.
TopicConnection	Pub/sub	`TopicSessions`, and consists of a connection to a JMS pub/sub provider created by `TopicConnectionFactory`.

To learn how to use the Connection class within an application, see Chapter 5, "Developing a Basic JMS Application," or the javax.jms.Connection Javadoc at http://java.sun.com/javaee/5/docs/api/javax/jms/Connection.html.

Session

A Session object defines a serial order for the messages produced and consumed, and can create multiple message producers and message consumers. The same thread can be used for producing and consuming messages. If an application wants to have a separate thread for producing and consuming messages, the application should create a separate session for each function.

A Session is created by a Connection (see Connection).

WebLogic JMS Session Guidelines

The JMS 1.1 Specification, at http://java.sun.com/products/jms/docs.html, allows for a generic session to have a MessageConsumer for any type of Destination object. However, WebLogic JMS does not support having both types of MessageConsumer (QueueConsumer and TopicSubscriber) for a single session. In addition, having multiple consumers for a single session is not a common practice. The following commonly-used scenarios are supported, however:

Using a single session with both a QueueSender and a TopicSubscriber (and vice-versa: QueueConsumer and TopicPublisher).
Multiple MessageProducers of any type.

Note:
A session and its message producers and consumers can only be accessed by one thread at a time. Their behavior is undefined if multiple threads access them simultaneously.

Session Subclasses

The following table describes the Session subclasses.

Table 2-6 Session Subclasses

Subclass. . .	In Messaging Model. . .	Provides a Context for. . .
QueueSession	PTP	Producing and consuming messages for a JMS PTP provider. Created by QueueConnection.
TopicSession	Pub/sub	Producing and consuming messages for a JMS pub/sub provider. Created by TopicConnection.

To learn how to use the Session class within an application, see Chapter 5, "Developing a Basic JMS Application," or the javax.jms.Session, at http://java.sun.com/javaee/5/docs/api/javax/jms/Session.html, and weblogic.jms.extensions.WLSession javadocs.

Non-Transacted Session

In a non-transacted session, the application creating the session selects one of the five acknowledge modes defined in the following table.

Table 2-7 Acknowledge Modes Used for Non-Transacted Sessions

Acknowledge Mode	Description
AUTO_ACKNOWLEDGE	The `Session` object acknowledges receipt of a message once the receiving application method has returned from processing it.
CLIENT_ACKNOWLEDGE	The `Session` object relies on the application to call an acknowledge method on a received message. Once the method is called, the session acknowledges all messages received since the last acknowledge. This mode allows an application to receive, process, and acknowledge a batch of messages with one call. Note: In the Administration Console, if the Acknowledge Policy attribute on the connection factory is set to `Previous`, but you want to acknowledge all received messages for a given session, then use the last message to invoke the acknowledge method. For more information on the Acknowledge Policy attribute, see "JMS Connection Factory: Configuration: General" in the Oracle WebLogic Server Administration Console Help.
DUPS_OK_ACKNOWLEDGE	The `Session` object acknowledges receipt of a message once the receiving application method has returned from processing it; duplicate acknowledges are permitted. This mode is most efficient in terms of resource usage. Note: You should avoid using this mode if your application cannot handle duplicate messages. Duplicate messages may be sent if an initial attempt to deliver a message fails.
NO_ACKNOWLEDGE	No acknowledge is required. Messages sent to a `NO_ACKNOWLEDGE` session are immediately deleted from the server. Messages received in this mode are not recovered, and as a result messages may be lost and/or duplicate message may be delivered if an initial attempt to deliver a message fails. This mode is supported for applications that do not require the quality of service provided by session acknowledge, and that do not want to incur the associated overhead. Note: You should avoid using this mode if your application cannot handle lost or duplicate messages. Duplicate messages may be sent if an initial attempt to deliver a message fails.
MULTICAST_NO_ACKNOWLEDGE	Multicast mode with no acknowledge required. Messages sent to a `MULTICAST_NO_ACKNOWLEDGE` session share the same characteristics as `NO_ACKNOWLEDGE` mode, described previously. This mode is supported for applications that want to support multicasting, and that do not require the quality of service provided by session acknowledge. For more information on multicasting, see Chapter 8, "Using Multicasting with WebLogic JMS." Note: Use only with topics. You should avoid using this mode if your application cannot handle lost or duplicate messages. Duplicate messages may be sent if an initial attempt to deliver a message fails.

Transacted Session

In a transacted session, only one transaction is active at any given time. Any number of messages sent or received during a transaction are treated as an atomic unit.

When you create a transacted session, the acknowledge mode is ignored. When an application commits a transaction, all the messages that the application received during the transaction are acknowledged by the messaging system and messages it sent are accepted for delivery. If an application rolls back a transaction, the messages that the application received during the transaction are not acknowledged and messages it sent are discarded.

JMS can participate in distributed transactions with other Java services, such as EJB, that use the Java Transaction API (JTA). Transacted sessions do not support this capability as the transaction is restricted to accessing the messages associated with that session. For more information about using JMS with JTA, see Using JTA User Transactions.

Destination

A Destination object can be either a queue or topic, encapsulating the address syntax for a specific provider. The JMS specification does not define a standard address syntax due to the variations in syntax between providers.

Similar to a connection factory, an administrator defines and configures the destination and the WebLogic Server adds it to the JNDI space during startup. Applications can also create temporary destinations that exist only for the duration of the JMS connection in which they are created.

Note:

Administrators can also configure a distributed destination, which is a single set of destinations (queues or topics) that are accessible as a single, logical destination to a client. For more information, see Distributed Destinations.

On the client side, Queue and Topic objects are handles to the object on the server. Their methods only return their names. To access them for messaging, you create message producers and consumers that attach to them.

A destination supports concurrent use, enabling multiple threads to access the object simultaneously. JMS Queues and Topics extend javax.jms.Destination, described at http://java.sun.com/javaee/5/docs/api/javax/jms/Destination.html.

Note:

For this release, you can use the JMS Version 1.1 specification destination objects or you can choose to use the subclasses.

The following table describes the Destination subclasses.

Table 2-8 Destination Subclasses

Subclass	Messaging Model	Manages Messages for
Queue	PTP	JMS point-to-point provider.
TemporaryQueue	PTP	JMS point-to-point provider, and exists for the duration of the JMS connection in which the messages are created. A temporary queue can be consumed only by the queue connection that created it.
Topic	Pub/sub	JMS pub/sub provider.
TemporaryTopic	Pub/sub	JMS pub/sub provider, and exists for the duration of the JMS connection in which the messages are created. A temporary topic can be consumed only by the topic connection that created it.

Note:

An application has the option of browsing queues by creating a QueueBrowser object in its queue session. This object produces a snapshot of the messages in the queue at the time the queue browser is created. The application can view the messages in the queue, but the messages are not considered read and are not removed from the queue. For more information about browsing queues, see Setting and Browsing Message Header and Property Fields.

To learn how to use the Destination class within an application, see Chapter 5, "Developing a Basic JMS Application," or the javax.jms.Destination Javadoc at http://java.sun.com/javaee/5/docs/api/javax/jms/Destination.html.

Distributed Destinations

A distributed destination resource is a single set of destinations (queues or topics) that are accessible as a single, logical destination to a client (for example, a distributed topic has its own JNDI name). The members of the set are typically distributed across multiple servers within a cluster, with each member belonging to a separate JMS server. Applications that use a distributed destination are more highly available than applications that use standalone destinations because WebLogic JMS provides load balancing and failover for the members of a distributed destination in a cluster.

For more information on using a distributed destination with your applications, see Chapter 9, "Using Distributed Destinations."
For instructions on configuring a distributed queue destination, see "Configure uniform distributed queues" in the Oracle WebLogic Server Administration Console Help.
For instructions on configuring a distributed topic destination, see "Configure uniform distributed topics" in the Oracle WebLogic Server Administration Console Help.

MessageProducer and MessageConsumer

A MessageProducer sends messages to a queue or topic. A MessageConsumer receives messages from a queue or topic. Message producers and consumers operate independently of one another. Message producers generate and send messages regardless of whether a message consumer has been created and is waiting for a message, and vice versa.

A Session (see Session) creates the MessageProducers and MessageConsumers that are attached to queues and topics.

The message sender and receiver objects are created as subclasses of the MessageProducer and MessageConsumer classes.

Note:

For this release, you can use the JMS Version 1.1 specification message producer and consumer objects or you can choose to use the subclasses.

The following table describes the MessageProducer and MessageConsumer subclasses.

Table 2-9 MessageProducer and MessageConsumer Subclasses

Subclass	In Messaging Model	Performs the Following Function
QueueSender	PTP	Sends messages for a JMS point-to-point provider.
QueueReceiver	PTP	Receives messages for a JMS point-to-point provider.
TopicPublisher	Pub/sub	Sends messages for a JMS pub/sub provider.
TopicSubscriber	Pub/sub	Receives messages for a JMS pub/sub provider.

The PTP model, as shown in the figure Figure 2-3, allows multiple sessions to receive messages from the same queue. However, a message can only be delivered to one queue receiver. When there are multiple queue receivers, WebLogic JMS defines the next queue receiver that will receive a message on a first-come, first-serve basis.

The pub/sub model, as shown in the figure Figure 2-4, allows messages to be delivered to multiple topic subscribers. Topic subscribers can be durable or non-durable, as described in Setting Up Durable Subscriptions.

An application can use the same JMS connection to both publish and subscribe to a topic. Because topic messages can be delivered to all subscribers, an application can receive messages it has published itself. To prevent clients from receiving messages that they publish, a JMS application can set a noLocal attribute on the topic subscriber, as described in Step 5: Create Message Producers and Message Consumers.

To learn how to use the MessageProducer and MessageConsumer classes within an application, see Setting Up a JMS Application, or the javax.jms.MessageProducer (at http://java.sun.com/javaee/5/docs/api/javax/jms/MessageProducer.html) and javax.jms.MessageConsumer (at http://java.sun.com/javaee/5/docs/api/javax/jms/MessageConsumer.html) Javadoc.

Message

A Message encapsulates the information exchanged by applications. This information includes three components:

Message Header Fields
Message Property Fields
Message Body

Message Header Fields

Every JMS message contains a standard set of header fields that is included by default and available to message consumers. Some fields can be set by the message producers.

For information about setting message header fields, see Setting and Browsing Message Header and Property Fields, or to the javax.jms.Message Javadoc, at http://java.sun.com/javaee/5/docs/api/javax/jms/Message.html.

The following table describes the fields in the message headers and shows how values are defined for each field.

Table 2-10 Message Header Fields

Field	Description	Defined by
JMSCorrelationID	Specifies one of the following: a WebLogic `JMSMessageID` (described later in this table), an application-specific string, or a `byte[]` array. The `JMSCorrelationID` is used to correlate messages and is set directly on the message by the application before `send()`. There are two common applications for this field. The first application is to link messages by setting up a request/response scheme, as follows: When an application sends a message, it stores the `JMSMessageID` value assigned to it. When an application receives the message, it copies the `JMSMessageID` into the `JMSCorrelationID` field of a response message that it sends back to the sending application. The second application is to use the `JMSCorrelationID` field to carry any String you choose, enabling a series of messages to be linked with some application-determined value.	Application
JMSDeliveryMode	Specifies `PERSISTENT` or `NON_PERSISTENT` messaging. This field is set on the producer or as parameter sent by the application before `send()`. When a persistent message is sent, it is stored in the WebLogic Persistent Store. The `send()` operation is not considered successful until delivery of the message can be guaranteed. A persistent message is guaranteed to be delivered at least once. WebLogic JMS does not store non-persistent messages in the persistent store. This mode of operation provides the lowest overhead. They are guaranteed to be delivered at least once unless there is a system failure, in which case messages may be lost. If a connection is closed or recovered, all non-persistent messages that have not yet been acknowledged will be redelivered. Once a non-persistent message is acknowledged, it will not be redelivered. This value is overwritten by a call to `producer.send()`, setting this value directly on the message has no effect. The values set by the producer can be queried using the message supplied to `producer.send()` or when the message is received by a consumer.	`send()` method
JMSDeliveryTime	Defines the earliest absolute time at which a message can be delivered to a consumer. This field is set by the application before `send()` and depends on `timeToDeliver`, which is set on the producer. This field can be used to sort messages in a destination and to select messages. For purposes of data type conversion, the `JMSDeliveryTime` is a long integer.	`send()` method
JMSDestination	Specifies the destination (queue or topic) to which the message is to be delivered. This field is set when creating producer or as parameter sent by the application before `send()`. This value is overwritten by a call to `producer.send()`, setting this value directly on the message has no effect. The values set by the producer can be queried using the message supplied to `producer.send()` or when the message is received by a consumer. When a message is received, its destination value must be equivalent to the value assigned when it was sent.	`send()` method
JMSExpiration	Specifies the expiration, or time-to-live value, for a message. This field is set by the application before `send()`. Depends on `timeToLive`, which is set on the producer or as a parameter sent by the application to `send()`. WebLogic JMS calculates the `JMSExpiration` value as the sum of the application's time-to-live and the current GMT. If the application specifies time-to-live as 0, `JMSExpiration` is set to 0, which means the message never expires. WebLogic JMS removes expired messages from the system to prevent their delivery.	`send()` method
JMSMessageID	Contains a string value that uniquely identifies each message sent by a JMS Provider.This field is set internally by `send()`. All `JMSMessageID`s start with an `ID:` prefix. This value is overwritten by a call to `producer.send()`, setting this value directly on the message has no effect. The values set by the producer can be queried using the message supplied to `producer.send()` or when the message is received by a consumer. When the message is received, it contains a provider-assigned value.	`send()` method
JMSPriority	Specifies the priority level. This field is set on the producer or as parameter sent by the application before `send()`. JMS defines ten priority levels, 0 to 9, 0 being the lowest priority. Levels 0-4 indicate gradations of normal priority, and level 5-9 indicate gradations of expedited priority. When the message is received, it contains the value specified by the method sending the message. You can sort destinations by priority by configuring a destination key, as described in "Configure destination keys" in the Oracle WebLogic Server Administration Console Help.	`send()` method
JMSRedelivered	Specifies a flag set when a message is redelivered because no acknowledge was received. This flag is of interest to a receiving application. If set, the flag indicates that JMS may have delivered the message previously because one of the following is true: The application has already received the message, but did not acknowledge it. The session's `recover()` method was called to restart the session beginning after the last acknowledged message. For more information about the `recover()` method, see Recovering Received Messages.	WebLogic JMS
JMSReplyTo	Specifies a queue or topic to which reply messages should be sent. This field is set directly on the message by the application before `send()`. This feature can be used with the `JMSCorrelationID` header field to coordinate request/response messages. Simply setting the `JMSReplyTo` field does not guarantee a response; it simply enables the receiving application to respond.	Application
JMSTimestamp	Contains the time at which the message was sent. WebLogic JMS writes the timestamp in the message when it accepts the message for delivery, not when the application sends the message. When the message is received, it contains the timestamp. The value stored in the field is a Java millis time value.	WebLogic JMS
JMSType	Specifies the message type identifier (String) set directly on the message by the application before `send()`. The JMS specification allows some flexibility with this field in order to accommodate diverse JMS providers. Some messaging systems allow application-specific message types to be used. For such systems, the `JMSType` field could be used to hold a message type ID that provides access to the stored type definitions. WebLogic JMS does not restrict the use of this field.	Application

Message Property Fields

The property fields of a message contain header fields added by the sending application. The properties are standard Java name/value pairs. Property names must conform to the message selector syntax specifications defined in the javax.jms.Message Javadoc, at http://java.sun.com/javaee/5/docs/api/javax/jms/Message.html. The following values are valid: boolean, byte, double, float, int, long, short, and String.

WebLogic Server supports the use of the following JMS (JMSX) defined properties as defined in the JMS 1.1. Specification, at http://java.sun.com/products/jms/docs.html:

Table 2-11 JMSX Property

Type	Description
JMSXUserID	System generated property that identifies the user sending the message. See Using the JMSXUserID Property.
JMSXDeliveryCount	System generated property that specifies the number of message delivery attempts where first attempt is 1.
JMSXGroupID	Identity of the message group.
JMSXGroupSeq	Sequence number of a message within a group.

Although message property fields may be used for application-specific purposes, JMS provides them primarily for use in message selectors. You determine how the JMS properties are used in your environment. You may choose to include them in some messages and omit them from others depending upon your processing criteria. For more information, see:

Setting and Browsing Message Header and Property Fields
Filtering Messages
JMS 1.1. Specification, described at http://java.sun.com/products/jms/docs.html

Message Body

A message body contains the content being delivered from producer to consumer.

The following table describes the types of messages defined by JMS. All message types extend javax.jms.Message, at http://java.sun.com/javaee/5/docs/api/javax/jms/Message.html, which consists of message headers and properties, but no message body.

Table 2-12 JMS Message Types

Type	Description
javax.jms.BytesMessage	Stream of uninterpreted bytes, which must be understood by the sender and receiver. The access methods for this message type are stream-oriented readers and writers based on `java.io.DataInputStream` and `java.io.DataOutputStream`. See `http://java.sun.com/javaee/5/docs/api/javax/jms/BytesMessage.html`.
javax.jms.MapMessage	Set of name/value pairs in which the names are strings and the values are Java primitive types. Pairs can be read sequentially or randomly, by specifying a name.
javax.jms.ObjectMessage	Single serializable Java object. See `http://java.sun.com/javaee/5/docs/api/javax/jms/ObjectMessage.html`.
javax.jms.StreamMessage	Similar to a BytesMessage, except that only Java primitive types are written to or read from the stream. See `http://java.sun.com/javaee/5/docs/api/javax/jms/StreamMessage.html`.
javax.jms.TextMessage	Single String. The TextMessage can also contain XML content. See `http://java.sun.com/javaee/5/docs/api/javax/jms/TextMessage.html`.
weblogic.jms.extensions.XMLMessage	XML content. Use of the XMLMessage type facilitates message filtering, which is more complex when performed on XML content shipped in a TextMessage.

For more information, see the javax.jms.Message Javadoc at http://java.sun.com/javaee/5/docs/api/javax/jms/Message.html. For more information about the access methods and, if applicable, the conversion charts associated with a particular message type, see the Javadoc for that message type.

ServerSessionPoolFactory

Note:

Session pool and connection consumer configuration objects are deprecated in this release of WebLogic Server. They are not a required part of the Java EE specification, do not support JTA user transactions, and are largely superseded by message-driven beans (MDBs), which are simpler, easier to manage, and more capable. For more information on designing MDBs, see "Message-Driven EJBs" in Programming WebLogic Enterprise JavaBeans for Oracle WebLogic Server.

A server session pool is a WebLogic-specific JMS feature that enables you to process messages concurrently. A server session pool factory is used to create a server-side ServerSessionPool.

WebLogic JMS defines one ServerSessionPoolFactory object, by default: weblogic.jms.extensions.ServerSessionPoolFactory:<name>, where <name> specifies the name of the JMS server to which the session pool is created. The WebLogic Server adds the default server session pool factory to the JNDI space during startup and the application subsequently retrieves the server session pool factory using WebLogic JNDI.

To learn how to use the server session pool factory within an application, see Defining Server Session Pools, or the weblogic.jms.extnesions.ServerSessionPoolFactory Javadoc.

ServerSessionPool

A ServerSessionPool application server object provides a pool of server sessions that connection consumers can retrieve in order to process messages concurrently.

A ServerSessionPool is created by the ServerSessionPoolFactory object (see ServerSessionPoolFactory) obtained through a JNDI lookup.

To learn how to use the server session pool within an application, see Defining Server Session Pools, or the javax.jms.ServerSessionPool Javadoc at http://java.sun.com/javaee/5/docs/api/javax/jms/ServerSessionPool.html.

ServerSession

A ServerSession application server object enables you to associate a thread with a JMS session by providing a context for creating, sending, and receiving messages.

A ServerSession is created by a ServerSessionPool object, described in ServerSessionPool.

To learn how to use the server session within an application, see Defining Server Session Pools, or the javax.jms.ServerSession Javadoc at http://java.sun.com/javaee/5/docs/api/javax/jms/ServerSession.html.

ConnectionConsumer

A ConnectionConsumer object uses a server session to process received messages. If message traffic is heavy, the connection consumer can load each server session with multiple messages to minimize thread context switching. A ConnectionConsumer is created by a Connection object, described in Connection.

To learn how to use the connection consumers within an application, see Defining Server Session Pools, or the javax.jms.ConnectionConsumer Javadoc at http://java.sun.com/javaee/5/docs/api/javax/jms/ConnectionConsumer.html.

Note:

Connection consumer listeners run on the same JVM as the server.