javax.jms
Interface Session

All Known Subinterfaces:

QueueSession, TopicSession, XAQueueSession, XASession, XATopicSession

public abstract interface Session

extends java.lang.Runnable

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

A session serves several purposes:

• It is a factory for its message producers and consumers.
• It supplies provider-optimized message factories.
• It supports a single series of transactions that combine work spanning its producers and consumers into atomic units.
• A session defines a serial order for the messages it consumes and the messages it produces.
• A session retains messages it consumes until they have been acknowledged.
• A session serializes execution of message listeners registered with it's message consumers.

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.

Another typical use is to have one thread set up a Session by creating its producers and one or more asynchronous consumers. Since the JMS provider serializes execution of a Session's asynchronous consumers, they can safely share the resources of their session.

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

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.

A session may be optionally 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, its 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 or 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.

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 JTA, use of the session's commit and rollback methods in this context is prohibited.

JMS 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 JMS is targeted at systems vendors who will be integrating JMS into their application server products.

Version:

1.0 - 6 August 1998

Author:

Mark Hapner, Rich Burridge

See Also:

QueueSession, TopicSession, XASession

Field Summary

static int	AUTO_ACKNOWLEDGE With this acknowledgement mode, the session automatically acknowledges a client's receipt of a message when it has either successfully returned from a call to receive or the message listener it has called to process the message successfully returns.
static int	CLIENT_ACKNOWLEDGE With this acknowledgement mode, the client acknowledges a message by calling a message's acknowledge method.
static int	DUPS_OK_ACKNOWLEDGE This acknowledgement mode instructs the session to lazily acknowledge the delivery of messages.

Method Summary

void	close() Since a provider may allocate some resources on behalf of a Session outside the JVM, clients should close them when they are not needed.
void	commit() Commit all messages done in this transaction and releases any locks currently held.
BytesMessage	createBytesMessage() Create a BytesMessage.
MapMessage	createMapMessage() Create a MapMessage.
Message	createMessage() Create a Message.
ObjectMessage	createObjectMessage() Create an ObjectMessage.
ObjectMessage	createObjectMessage(java.io.Serializable object) Create an initialized ObjectMessage.
StreamMessage	createStreamMessage() Create a StreamMessage.
TextMessage	createTextMessage() Create a TextMessage.
TextMessage	createTextMessage(java.lang.StringBuffer stringBuffer) Create an initialized TextMessage.
MessageListener	getMessageListener() Return the session's distinguished message listener.
boolean	getTransacted() Is the session in transacted mode?
void	recover() Stop message delivery in this session, and restart sending messages with the oldest unacknowledged message.
void	rollback() Rollback any messages done in this transaction and releases any locks currently held.
void	setMessageListener(MessageListener listener) Set the session's distinguished message listener.

Methods inherited from interface java.lang.Runnable

run

Field Detail

AUTO_ACKNOWLEDGE

public static final int AUTO_ACKNOWLEDGE

With this acknowledgement mode, the session automatically acknowledges a client's receipt of a message when it has either successfully returned from a call to receive or the message listener it has called to process the message successfully returns.

CLIENT_ACKNOWLEDGE

public static final int CLIENT_ACKNOWLEDGE

With this acknowledgement mode, the client acknowledges a message by calling a message's acknowledge method. Acknowledging a 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 over-run so that clients are not driven to resource exhaustion and ensuing failure when some resource they are using is temporarily blocked.

DUPS_OK_ACKNOWLEDGE

public static final int DUPS_OK_ACKNOWLEDGE

This acknowledgement mode instructs the session to lazily acknowledge the delivery of messages. This is likely to result in the delivery of some duplicate messages if JMS fails, it should only be used by consumers that are tolerant of duplicate messages. Its benefit is the reduction of session overhead achieved by minimizing the work the session does to prevent duplicates.

Method Detail

createBytesMessage

public BytesMessage createBytesMessage()

                                throws JMSException

Create a BytesMessage. A BytesMessage is used to send a message containing a stream of uninterpreted bytes.

Throws:

JMSException - if JMS fails to create this message due to some internal error.

createMapMessage

public MapMessage createMapMessage()

                            throws JMSException

Create a MapMessage. A MapMessage is used to send a self-defining set of name-value pairs where names are Strings and values are Java primitive types.

Throws:

JMSException - if JMS fails to create this message due to some internal error.

createMessage

public Message createMessage()

                      throws JMSException

Create a Message. The Message interface is the root interface of all JMS messages. It holds all the standard message header information. It can be sent when a message containing only header information is sufficient.

Throws:

JMSException - if JMS fails to create this message due to some internal error.

createObjectMessage

public ObjectMessage createObjectMessage()

                                  throws JMSException

Create an ObjectMessage. An ObjectMessage is used to send a message that containing a serializable Java object.

Throws:

JMSException - if JMS fails to create this message due to some internal error.

createObjectMessage

public ObjectMessage createObjectMessage(java.io.Serializable object)

                                  throws JMSException

Create an initialized ObjectMessage. An ObjectMessage is used to send a message that containing a serializable Java object.

Parameters:

object - the object to use to initialize this message.

Throws:

JMSException - if JMS fails to create this message due to some internal error.

createStreamMessage

public StreamMessage createStreamMessage()

                                  throws JMSException

Create a StreamMessage. A StreamMessage is used to send a self-defining stream of Java primitives.

Throws:

JMSException - if JMS fails to create this message due to some internal error.

createTextMessage

public TextMessage createTextMessage()

                              throws JMSException

Create a TextMessage. A TextMessage is used to send a message containing a StringBuffer.

Throws:

JMSException - if JMS fails to create this message due to some internal error.

createTextMessage

public TextMessage createTextMessage(java.lang.StringBuffer stringBuffer)

                              throws JMSException

Create an initialized TextMessage. A TextMessage is used to send a message containing a StringBuffer.

Parameters:

stringBuffer - the string buffer used to initialize this message.

Throws:

JMSException - if JMS fails to create this message due to some internal error.

getTransacted

public boolean getTransacted()

                      throws JMSException

Is the session in transacted mode?

Returns:

true if in transacted mode

Throws:

JMSException - if JMS fails to return the transaction mode due to internal error in JMS Provider.

commit

public void commit()

            throws JMSException

Commit all messages done in this transaction and releases any locks currently held.

Throws:

JMSException - if JMS implementation fails to commit the the transaction due to some internal error.

TransactionRolledBackException - if the transaction gets rolled back due to some internal error during commit.

rollback

public void rollback()

              throws JMSException

Rollback any messages done in this transaction and releases any locks currently held.

Throws:

JMSException - if JMS implementation fails to rollback the the transaction due to some internal error.

close

public void close()

           throws JMSException

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

Throws:

JMSException - if JMS implementation fails to close a Session due to some internal error.

recover

public void recover()

             throws JMSException

Stop message delivery in this session, and restart sending messages 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.

Throws:

JMSException - if JMS implementation fails to stop message delivery and restart message send due to due to some internal error.

getMessageListener

public MessageListener getMessageListener()

                                   throws JMSException

Return the session's distinguished message listener.

Returns:

the message listener associted with this session.

Throws:

JMSException - if JMS fails to get the message listener due to an internal error in JMS Provider.

See Also:

setMessageListener(javax.jms.MessageListener), ServerSessionPool, ServerSession

setMessageListener

public void setMessageListener(MessageListener listener)

                        throws JMSException

Set the session's distinguished message listener. When it 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.

Parameters:

listener - the message listener to associate with this session.

Throws:

JMSException - if JMS fails to set the message listener due to an internal error in JMS Provider.

See Also:

getMessageListener(), ServerSessionPool, ServerSession