Home » jboss-javaee-sources » javax » jms » [javadoc | source]
javax.jms
public interface: Session [javadoc | source]

All Implemented Interfaces:
    Runnable

All Known Implementing Classes:
    XASession, XAQueueSession, TopicSession, XATopicSession, QueueSession

A Session object is a single-threaded context for producing and consuming messages. Although it may allocate provider resources outside the Java virtual machine (JVM), it is considered a lightweight JMS object.

A session serves several purposes:

A session can create and service multiple message producers and consumers.

One typical use is to have a thread block on a synchronous MessageConsumer until a message arrives. The thread may then use one or more of the Session's MessageProducers.

If a client desires to have one thread produce messages while others consume them, the client should use a separate session for its producing thread.

Once a connection has been started, any session with one or more registered message listeners is dedicated to the thread of control that delivers messages to it. It is erroneous for client code to use this session or any of its constituent objects from another thread of control. The only exception to this rule is the use of the session or connection close method.

It should be easy for most clients to partition their work naturally into sessions. This model allows clients to start simply and incrementally add message processing complexity as their need for concurrency grows.

The close method is the only session method that can be called while some other session method is being executed in another thread.

A session may be specified as transacted. Each transacted session supports a single series of transactions. Each transaction groups a set of message sends and a set of message receives into an atomic unit of work. In effect, transactions organize a session's input message stream and output message stream into series of atomic units. When a transaction commits, its atomic unit of input is acknowledged and its associated atomic unit of output is sent. If a transaction rollback is done, the transaction's sent messages are destroyed and the session's input is automatically recovered.

The content of a transaction's input and output units is simply those messages that have been produced and consumed within the session's current transaction.

A transaction is completed using either its session's commit method or its session's rollback method. The completion of a session's current transaction automatically begins the next. The result is that a transacted session always has a current transaction within which its work is done.

The Java Transaction Service (JTS) or some other transaction monitor may be used to combine a session's transaction with transactions on other resources (databases, other JMS sessions, etc.). Since Java distributed transactions are controlled via the Java Transaction API (JTA), use of the session's commit and rollback methods in this context is prohibited.

The JMS API does not require support for JTA; however, it does define how a provider supplies this support.

Although it is also possible for a JMS client to handle distributed transactions directly, it is unlikely that many JMS clients will do this. Support for JTA in the JMS API is targeted at systems vendors who will be integrating the JMS API into their application server products.

Field Summary
static final  int AUTO_ACKNOWLEDGE    With this acknowledgment mode, the session automatically acknowledges a client's receipt of a message either when the session has successfully returned from a call to receive or when the message listener the session has called to process the message successfully returns. 
static final  int CLIENT_ACKNOWLEDGE    With this acknowledgment mode, the client acknowledges a consumed message by calling the message's acknowledge method. Acknowledging a consumed message acknowledges all messages that the session has consumed.

When client acknowledgment mode is used, a client may build up a large number of unacknowledged messages while attempting to process them. A JMS provider should provide administrators with a way to limit client overrun so that clients are not driven to resource exhaustion and ensuing failure when some resource they are using is temporarily blocked.

    Also see:
    javax.jms.Message#acknowledge()
 
static final  int DUPS_OK_ACKNOWLEDGE    This acknowledgment mode instructs the session to lazily acknowledge the delivery of messages. This is likely to result in the delivery of some duplicate messages if the JMS provider fails, so it should only be used by consumers that can tolerate duplicate messages. Use of this mode can reduce session overhead by minimizing the work the session does to prevent duplicates. 
static final  int SESSION_TRANSACTED    This value is returned from the method getAcknowledgeMode if the session is transacted. If a Session is transacted, the acknowledgement mode is ignored. 
Method from javax.jms.Session Summary:
close,   commit,   createBrowser,   createBrowser,   createBytesMessage,   createConsumer,   createConsumer,   createConsumer,   createDurableSubscriber,   createDurableSubscriber,   createMapMessage,   createMessage,   createObjectMessage,   createObjectMessage,   createProducer,   createQueue,   createStreamMessage,   createTemporaryQueue,   createTemporaryTopic,   createTextMessage,   createTextMessage,   createTopic,   getAcknowledgeMode,   getMessageListener,   getTransacted,   recover,   rollback,   run,   setMessageListener,   unsubscribe
Method from javax.jms.Session Detail:
 public  void close() throws JMSException
    Closes the session.

    Since a provider may allocate some resources on behalf of a session outside the JVM, clients should close the resources when they are not needed. Relying on garbage collection to eventually reclaim these resources may not be timely enough.

    There is no need to close the producers and consumers of a closed session.

    This call will block until a receive call or message listener in progress has completed. A blocked message consumer receive call returns null when this session is closed.

    Closing a transacted session must roll back the transaction in progress.

    This method is the only Session method that can be called concurrently.

    Invoking any other Session method on a closed session must throw a JMSException.IllegalStateException. Closing a closed session must not throw an exception.

 public  void commit() throws JMSException
    Commits all messages done in this transaction and releases any locks currently held.
 public QueueBrowser createBrowser(Queue queue) throws JMSException
    Creates a QueueBrowser object to peek at the messages on the specified queue.
 public QueueBrowser createBrowser(Queue queue,
    String messageSelector) throws JMSException
    Creates a QueueBrowser object to peek at the messages on the specified queue using a message selector.
 public BytesMessage createBytesMessage() throws JMSException
    Creates a BytesMessage object. A BytesMessage object is used to send a message containing a stream of uninterpreted bytes.
 public MessageConsumer createConsumer(Destination destination) throws JMSException
    Creates a MessageConsumer for the specified destination. Since Queue and Topic both inherit from Destination, they can be used in the destination parameter to create a MessageConsumer.
 public MessageConsumer createConsumer(Destination destination,
    String messageSelector) throws JMSException
    Creates a MessageConsumer for the specified destination, using a message selector. Since Queue and Topic both inherit from Destination, they can be used in the destination parameter to create a MessageConsumer.

    A client uses a MessageConsumer object to receive messages that have been sent to a destination.

 public MessageConsumer createConsumer(Destination destination,
    String messageSelector,
    boolean NoLocal) throws JMSException
    Creates MessageConsumer for the specified destination, using a message selector. This method can specify whether messages published by its own connection should be delivered to it, if the destination is a topic.

    Since Queue and Topic both inherit from Destination, they can be used in the destination parameter to create a MessageConsumer.

    A client uses a MessageConsumer object to receive messages that have been published to a destination.

    In some cases, a connection may both publish and subscribe to a topic. The consumer NoLocal attribute allows a consumer to inhibit the delivery of messages published by its own connection. The default value for this attribute is False. The noLocal value must be supported by destinations that are topics.

 public TopicSubscriber createDurableSubscriber(Topic topic,
    String name) throws JMSException
    Creates a durable subscriber to the specified topic.

    If a client needs to receive all the messages published on a topic, including the ones published while the subscriber is inactive, it uses a durable TopicSubscriber. The JMS provider retains a record of this durable subscription and insures that all messages from the topic's publishers are retained until they are acknowledged by this durable subscriber or they have expired.

    Sessions with durable subscribers must always provide the same client identifier. In addition, each client must specify a name that uniquely identifies (within client identifier) each durable subscription it creates. Only one session at a time can have a TopicSubscriber for a particular durable subscription.

    A client can change an existing durable subscription by creating a durable TopicSubscriber with the same name and a new topic and/or message selector. Changing a durable subscriber is equivalent to unsubscribing (deleting) the old one and creating a new one.

    In some cases, a connection may both publish and subscribe to a topic. The subscriber NoLocal attribute allows a subscriber to inhibit the delivery of messages published by its own connection. The default value for this attribute is false.

 public TopicSubscriber createDurableSubscriber(Topic topic,
    String name,
    String messageSelector,
    boolean noLocal) throws JMSException
    Creates a durable subscriber to the specified topic, using a message selector and specifying whether messages published by its own connection should be delivered to it.

    If a client needs to receive all the messages published on a topic, including the ones published while the subscriber is inactive, it uses a durable TopicSubscriber. The JMS provider retains a record of this durable subscription and insures that all messages from the topic's publishers are retained until they are acknowledged by this durable subscriber or they have expired.

    Sessions with durable subscribers must always provide the same client identifier. In addition, each client must specify a name which uniquely identifies (within client identifier) each durable subscription it creates. Only one session at a time can have a TopicSubscriber for a particular durable subscription. An inactive durable subscriber is one that exists but does not currently have a message consumer associated with it.

    A client can change an existing durable subscription by creating a durable TopicSubscriber with the same name and a new topic and/or message selector. Changing a durable subscriber is equivalent to unsubscribing (deleting) the old one and creating a new one.

 public MapMessage createMapMessage() throws JMSException
    Creates a MapMessage object. A MapMessage object is used to send a self-defining set of name-value pairs, where names are String objects and values are primitive values in the Java programming language.
 public Message createMessage() throws JMSException
    Creates a Message object. The Message interface is the root interface of all JMS messages. A Message object holds all the standard message header information. It can be sent when a message containing only header information is sufficient.
 public ObjectMessage createObjectMessage() throws JMSException
    Creates an ObjectMessage object. An ObjectMessage object is used to send a message that contains a serializable Java object.
 public ObjectMessage createObjectMessage(Serializable object) throws JMSException
    Creates an initialized ObjectMessage object. An ObjectMessage object is used to send a message that contains a serializable Java object.
 public MessageProducer createProducer(Destination destination) throws JMSException
    Creates a MessageProducer to send messages to the specified destination.

    A client uses a MessageProducer object to send messages to a destination. Since Queue and Topic both inherit from Destination, they can be used in the destination parameter to create a MessageProducer object.

 public Queue createQueue(String queueName) throws JMSException
    Creates a queue identity given a Queue name.

    This facility is provided for the rare cases where clients need to dynamically manipulate queue identity. It allows the creation of a queue identity with a provider-specific name. Clients that depend on this ability are not portable.

    Note that this method is not for creating the physical queue. The physical creation of queues is an administrative task and is not to be initiated by the JMS API. The one exception is the creation of temporary queues, which is accomplished with the createTemporaryQueue method.

 public StreamMessage createStreamMessage() throws JMSException
    Creates a StreamMessage object. A StreamMessage object is used to send a self-defining stream of primitive values in the Java programming language.
 public TemporaryQueue createTemporaryQueue() throws JMSException
    Creates a TemporaryQueue object. Its lifetime will be that of the Connection unless it is deleted earlier.
 public TemporaryTopic createTemporaryTopic() throws JMSException
    Creates a TemporaryTopic object. Its lifetime will be that of the Connection unless it is deleted earlier.
 public TextMessage createTextMessage() throws JMSException
    Creates a TextMessage object. A TextMessage object is used to send a message containing a String object.
 public TextMessage createTextMessage(String text) throws JMSException
    Creates an initialized TextMessage object. A TextMessage object is used to send a message containing a String.
 public Topic createTopic(String topicName) throws JMSException
    Creates a topic identity given a Topic name.

    This facility is provided for the rare cases where clients need to dynamically manipulate topic identity. This allows the creation of a topic identity with a provider-specific name. Clients that depend on this ability are not portable.

    Note that this method is not for creating the physical topic. The physical creation of topics is an administrative task and is not to be initiated by the JMS API. The one exception is the creation of temporary topics, which is accomplished with the createTemporaryTopic method.

 public int getAcknowledgeMode() throws JMSException
    Returns the acknowledgement mode of the session. The acknowledgement mode is set at the time that the session is created. If the session is transacted, the acknowledgement mode is ignored.
 public MessageListener getMessageListener() throws JMSException
    Returns the session's distinguished message listener (optional).
 public boolean getTransacted() throws JMSException
    Indicates whether the session is in transacted mode.
 public  void recover() throws JMSException
    Stops message delivery in this session, and restarts message delivery with the oldest unacknowledged message.

    All consumers deliver messages in a serial order. Acknowledging a received message automatically acknowledges all messages that have been delivered to the client.

    Restarting a session causes it to take the following actions:

    • Stop message delivery
    • Mark all messages that might have been delivered but not acknowledged as "redelivered"
    • Restart the delivery sequence including all unacknowledged messages that had been previously delivered. Redelivered messages do not have to be delivered in exactly their original delivery order.
 public  void rollback() throws JMSException
    Rolls back any messages done in this transaction and releases any locks currently held.
 public  void run()
    Optional operation, intended to be used only by Application Servers, not by ordinary JMS clients.
 public  void setMessageListener(MessageListener listener) throws JMSException
    Sets the session's distinguished message listener (optional).

    When the distinguished message listener is set, no other form of message receipt in the session can be used; however, all forms of sending messages are still supported.

    This is an expert facility not used by regular JMS clients.

 public  void unsubscribe(String name) throws JMSException
    Unsubscribes a durable subscription that has been created by a client.

    This method deletes the state being maintained on behalf of the subscriber by its provider.

    It is erroneous for a client to delete a durable subscription while there is an active MessageConsumer or TopicSubscriber for the subscription, or while a consumed message is part of a pending transaction or has not been acknowledged in the session.