javax.jms
Interface Session

All Superinterfaces:

java.lang.Runnable

All Known Subinterfaces:

QueueSession, TopicSession, XAQueueSession, XASession, XATopicSession

public interface Session

extends java.lang.Runnable

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:

• 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.
• It defines a serial order for the messages it consumes and the messages it produces.
• It retains messages it consumes until they have been acknowledged.
• It serializes execution of message listeners registered with its 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.

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.

See Also:

QueueSession, TopicSession, XASession

Field Summary

static 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 int	CLIENT_ACKNOWLEDGE With this acknowledgment mode, the client acknowledges a consumed message by calling the message's acknowledge method.
static int	DUPS_OK_ACKNOWLEDGE This acknowledgment mode instructs the session to lazily acknowledge the delivery of messages.

Method Summary

void	close() Closes the session.
void	commit() Commits all messages done in this transaction and releases any locks currently held.
BytesMessage	createBytesMessage() Creates a BytesMessage object.
MapMessage	createMapMessage() Creates a MapMessage object.
Message	createMessage() Creates a Message object.
ObjectMessage	createObjectMessage() Creates an ObjectMessage object.
ObjectMessage	createObjectMessage(java.io.Serializable object) Creates an initialized ObjectMessage object.
StreamMessage	createStreamMessage() Creates a StreamMessage object.
TextMessage	createTextMessage() Creates a TextMessage object.
TextMessage	createTextMessage(java.lang.String text) Creates an initialized TextMessage object.
MessageListener	getMessageListener() Returns the session's distinguished message listener (optional).
boolean	getTransacted() Indicates whether the session is in transacted mode.
void	recover() Stops message delivery in this session, and restarts message delivery with the oldest unacknowledged message.
void	rollback() Rolls back any messages done in this transaction and releases any locks currently held.
void	run() Optional operation, intended to be used only by Application Servers, not by ordinary JMS clients.
void	setMessageListener(MessageListener listener) Sets the session's distinguished message listener (optional).

Field Detail

AUTO_ACKNOWLEDGE

public 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.

CLIENT_ACKNOWLEDGE

public 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.

See Also:

Message.acknowledge()

DUPS_OK_ACKNOWLEDGE

public 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.

Method Detail

createBytesMessage

public BytesMessage createBytesMessage()
                                throws JMSException

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

Throws:

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

createMapMessage

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.

Throws:

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

createMessage

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.

Throws:

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

createObjectMessage

public ObjectMessage createObjectMessage()
                                  throws JMSException

Creates an ObjectMessage object. An ObjectMessage object is used to send a message that contains a serializable Java object.

Throws:

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

createObjectMessage

public ObjectMessage createObjectMessage(java.io.Serializable object)
                                  throws JMSException

Creates an initialized ObjectMessage object. An ObjectMessage object is used to send a message that contains a serializable Java object.

Parameters:

object - the object to use to initialize this message

Throws:

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

createStreamMessage

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.

Throws:

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

createTextMessage

public TextMessage createTextMessage()
                              throws JMSException

Creates a TextMessage object. A TextMessage object is used to send a message containing a String object.

Throws:

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

createTextMessage

public TextMessage createTextMessage(java.lang.String text)
                              throws JMSException

Creates an initialized TextMessage object. A TextMessage object is used to send a message containing a String.

Parameters:

text - the string used to initialize this message

Throws:

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

getTransacted

public boolean getTransacted()
                      throws JMSException

Indicates whether the session is in transacted mode.

Returns:

true if the session is in transacted mode

Throws:

JMSException - if the JMS provider fails to return the transaction mode due to some internal error.

commit

public void commit()
            throws JMSException

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

Throws:

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

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

IllegalStateException - if the method is not called by a transacted session.

rollback

public void rollback()
              throws JMSException

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

Throws:

JMSException - if the JMS provider fails to roll back the transaction due to some internal error.

IllegalStateException - if the method is not called by a transacted session.

close

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.

Throws:

JMSException - if the JMS provider fails to close the session due to some internal error.

recover

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.

Throws:

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

IllegalStateException - if the method is called by a transacted session.

getMessageListener

public MessageListener getMessageListener()
                                   throws JMSException

Returns the session's distinguished message listener (optional).

Returns:

the message listener associated with this session

Throws:

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

See Also:

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

setMessageListener

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.

Parameters:

listener - the message listener to associate with this session

Throws:

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

See Also:

getMessageListener(), ServerSessionPool, ServerSession

run

public void run()

Optional operation, intended to be used only by Application Servers, not by ordinary JMS clients.

Specified by:

run in interface java.lang.Runnable

See Also:

ServerSession