javax.jms
Interface Connection

All Known Subinterfaces:

QueueConnection, TopicConnection, XAQueueConnection, XATopicConnection

public interface Connection

A Connection object is a client's active connection to its JMS provider. It typically allocates provider resources outside the Java virtual machine (JVM).

Connections support concurrent use.

A connection serves several purposes:

• It encapsulates an open connection with a JMS provider. It typically represents an open TCP/IP socket between a client and a provider service daemon.
• Its creation is where client authentication takes place.
• It can specify a unique client identifier.
• It provides a ConnectionMetaData object.
• It supports an optional ExceptionListener object.

Because the creation of a connection involves setting up authentication and communication, a connection is a relatively heavyweight object. Most clients will do all their messaging with a single connection. Other more advanced applications may use several connections. The JMS API does not architect a reason for using multiple connections; however, there may be operational reasons for doing so.

A JMS client typically creates a connection, one or more sessions, and a number of message producers and consumers. When a connection is created, it is in stopped mode. That means that no messages are being delivered.

It is typical to leave the connection in stopped mode until setup is complete (that is, until all message consumers have been created). At that point, the client calls the connection's start method, and messages begin arriving at the connection's consumers. This setup convention minimizes any client confusion that may result from asynchronous message delivery while the client is still in the process of setting itself up.

A connection can be started immediately, and the setup can be done afterwards. Clients that do this must be prepared to handle asynchronous message delivery while they are still in the process of setting up.

A message producer can send messages while a connection is stopped.

See Also:

ConnectionFactory, QueueConnection, TopicConnection

Method Summary

void	close() Closes the connection.
java.lang.String	getClientID() Gets the client identifier for this connection.
ExceptionListener	getExceptionListener() Gets the ExceptionListener object for this connection.
ConnectionMetaData	getMetaData() Gets the metadata for this connection.
void	setClientID(java.lang.String clientID) Sets the client identifier for this connection.
void	setExceptionListener(ExceptionListener listener) Sets an exception listener for this connection.
void	start() Starts (or restarts) a connection's delivery of incoming messages.
void	stop() Temporarily stops a connection's delivery of incoming messages.

Method Detail

getClientID

public java.lang.String getClientID()
                             throws JMSException

Gets the client identifier for this connection.

This value is specific to the JMS provider. It is either preconfigured by an administrator in a ConnectionFactory object or assigned dynamically by the application by calling the setClientID method.

Returns:

the unique client identifier

Throws:

JMSException - if the JMS provider fails to return the client ID for this connection due to some internal error.

setClientID

public void setClientID(java.lang.String clientID)
                 throws JMSException

Sets the client identifier for this connection.

The preferred way to assign a JMS client's client identifier is for it to be configured in a client-specific ConnectionFactory object and transparently assigned to the Connection object it creates.

Alternatively, a client can set a connection's client identifier using a provider-specific value. The facility to set a connection's client identifier explicitly is not a mechanism for overriding the identifier that has been administratively configured. It is provided for the case where no administratively specified identifier exists. If one does exist, an attempt to change it by setting it must throw an IllegalStateException. If a client sets the client identifier explicitly, it must do so immediately after it creates the connection and before any other action on the connection is taken. After this point, setting the client identifier is a programming error that should throw an IllegalStateException.

The purpose of the client identifier is to associate a connection and its objects with a state maintained on behalf of the client by a provider. The only such state identified by the JMS API is that required to support durable subscriptions.

If another connection with the same clientID is already running when this method is called, the JMS provider should detect the duplicate ID and throw an InvalidClientIDException.

Parameters:

clientID - the unique client identifier

Throws:

JMSException - if the JMS provider fails to set the client ID for this connection due to some internal error.

InvalidClientIDException - if the JMS client specifies an invalid or duplicate client ID.

IllegalStateException - if the JMS client attempts to set a connection's client ID at the wrong time or when it has been administratively configured.

getMetaData

public ConnectionMetaData getMetaData()
                               throws JMSException

Gets the metadata for this connection.

Returns:

the connection metadata

Throws:

JMSException - if the JMS provider fails to get the connection metadata for this connection.

See Also:

ConnectionMetaData

getExceptionListener

public ExceptionListener getExceptionListener()
                                       throws JMSException

Gets the ExceptionListener object for this connection.

Returns:

the ExceptionListener for this connection

Throws:

JMSException - if the JMS provider fails to get the ExceptionListener for this connection.

setExceptionListener

public void setExceptionListener(ExceptionListener listener)
                          throws JMSException

Sets an exception listener for this connection.

If a JMS provider detects a serious problem with a connection, it informs the connection's ExceptionListener, if one has been registered. It does this by calling the listener's onException method, passing it a JMSException object describing the problem.

An exception listener allows a client to be notified of a problem asynchronously. Some connections only consume messages, so they would have no other way to learn their connection has failed.

A connection serializes execution of its ExceptionListener.

A JMS provider should attempt to resolve connection problems itself before it notifies the client of them.

Parameters:

listener - the exception listener

Throws:

JMSException - if the JMS provider fails to set the exception listener for this connection.

start

public void start()
           throws JMSException

Starts (or restarts) a connection's delivery of incoming messages. A call to start on a connection that has already been started is ignored.

Throws:

JMSException - if the JMS provider fails to start message delivery due to some internal error.

See Also:

stop()

stop

public void stop()
          throws JMSException

Temporarily stops a connection's delivery of incoming messages. Delivery can be restarted using the connection's start method. When the connection is stopped, delivery to all the connection's message consumers is inhibited: synchronous receives block, and messages are not delivered to message listeners.

This call blocks until receives and/or message listeners in progress have completed.

Stopping a connection has no effect on its ability to send messages. A call to stop on a connection that has already been stopped is ignored.

A call to stop must not return until delivery of messages has paused. This means that a client can rely on the fact that none of its message listeners will be called and that all threads of control waiting for receive calls to return will not return with a message until the connection is restarted. The receive timers for a stopped connection continue to advance, so receives may time out while the connection is stopped.

If message listeners are running when stop is invoked, the stop call must wait until all of them have returned before it may return. While these message listeners are completing, they must have the full services of the connection available to them.

Throws:

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

See Also:

start()

close

public void close()
           throws JMSException

Closes the connection.

Since a provider typically allocates significant resources outside the JVM on behalf of a connection, clients should close these 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 sessions, producers, and consumers of a closed connection.

Closing a connection causes all temporary destinations to be deleted.

When this method is invoked, it should not return until message processing has been shut down in an orderly fashion. This means that all message listeners that may have been running have returned, and that all pending receives have returned. A close terminates all pending message receives on the connection's sessions' consumers. The receives may return with a message or with null, depending on whether there was a message available at the time of the close. If one or more of the connection's sessions' message listeners is processing a message at the time when connection close is invoked, all the facilities of the connection and its sessions must remain available to those listeners until they return control to the JMS provider.

Closing a connection causes any of its sessions' transactions in progress to be rolled back. In the case where a session's work is coordinated by an external transaction manager, a session's commit and rollback methods are not used and the result of a closed session's work is determined later by the transaction manager. Closing a connection does NOT force an acknowledgment of client-acknowledged sessions.

Invoking the acknowledge method of a received message from a closed connection's session must throw an IllegalStateException. Closing a closed connection must NOT throw an exception.

Throws:

JMSException - if the JMS provider fails to close the connection due to some internal error. For example, a failure to release resources or to close a socket connection can cause this exception to be thrown.