Module jakarta.messaging

Package jakarta.jms

Interface MessageConsumer

All Superinterfaces:

AutoCloseable

All Known Subinterfaces:

QueueReceiver, TopicSubscriber

public interface MessageConsumer
extends AutoCloseable

A client uses a MessageConsumer object to receive messages from a destination. A MessageConsumer object is created by passing a Destination object to a message-consumer creation method supplied by a session.

MessageConsumer is the parent interface for all message consumers.

A MessageConsumer can be created with a message selector. A message selector allows the client to restrict the messages delivered to the message consumer to those that match the selector.

A client may either synchronously receive a MessageConsumer's messages or have the MessageConsumer asynchronously deliver them as they arrive.

For synchronous receipt, a client can request the next message from a MessageConsumer using one of its receive methods. There are several variations of receive that allow a client to poll or wait for the next message.

For asynchronous delivery, a client can register a MessageListener object with a MessageConsumer. As messages arrive at the MessageConsumer, it delivers them by calling the MessageListener's onMessage method.

It is a client programming error for a MessageListener to throw an exception.

Since:

JMS 1.0

Version:

Jakarta Messaging 2.0

See Also:

• QueueReceiver
• TopicSubscriber
• Session

Method Summary

Modifier and Type	Method	Description
void	close()	Closes the message consumer.
MessageListener	getMessageListener()	Gets the MessageConsumer's MessageListener.
String	getMessageSelector()	Gets this message consumer's message selector expression.
Message	receive()	Receives the next message produced for this message consumer.
Message	receive(long timeout)	Receives the next message that arrives within the specified timeout interval.
Message	receiveNoWait()	Receives the next message if one is immediately available.
void	setMessageListener(MessageListener listener)	Sets the MessageConsumer's MessageListener.

Method Details

getMessageSelector

String getMessageSelector()
                   throws JMSException

Gets this message consumer's message selector expression.

Returns:

this message consumer's message selector, or null if no message selector exists for the message consumer (that is, if the message selector was not set or was set to null or the empty string)

Throws:

JMSException - if the Jakarta Messaging provider fails to get the message selector due to some internal error.

getMessageListener

MessageListener getMessageListener()
                            throws JMSException

Gets the MessageConsumer's MessageListener.

This method must not be used in a Jakarta EE web or EJB application. Doing so may cause a JMSException to be thrown though this is not guaranteed.

Returns:

the MessageConsumer's MessageListener, or null if one was not set

Throws:

JMSException - if the Jakarta Messaging provider fails to get the MessageListener for one of the following reasons:

• an internal error has occurred or
• this method has been called in a Jakarta EE web or EJB application (though it is not guaranteed that an exception is thrown in this case)

See Also:

• setMessageListener(jakarta.jms.MessageListener)

setMessageListener

void setMessageListener(MessageListener listener)
                 throws JMSException

Sets the MessageConsumer's MessageListener.

Setting the the MessageListener to null is the equivalent of unsetting the MessageListener for the MessageConsumer.

The effect of calling this method while messages are being consumed by an existing listener or the MessageConsumer is being used to consume messages synchronously is undefined.

This method must not be used in a Jakarta EE web or EJB application. Doing so may cause a JMSException to be thrown though this is not guaranteed.

Parameters:

listener - the listener to which the messages are to be delivered

Throws:

JMSException - if the Jakarta Messaging provider fails to set the MessageConsumer's MessageListener for one of the following reasons:

• an internal error has occurred or
• this method has been called in a Jakarta EE web or EJB application (though it is not guaranteed that an exception is thrown in this case)

See Also:

• getMessageListener()

receive

Message receive()
         throws JMSException

Receives the next message produced for this message consumer.

This call blocks indefinitely until a message is produced or until this message consumer is closed.

If this receive is done within a transaction, the consumer retains the message until the transaction commits.

Returns:

the next message produced for this message consumer, or null if this message consumer is concurrently closed

Throws:

JMSException - if the Jakarta Messaging provider fails to receive the next message due to some internal error.

receive

Message receive(long timeout)
         throws JMSException

Receives the next message that arrives within the specified timeout interval.

This call blocks until a message arrives, the timeout expires, or this message consumer is closed. A timeout of zero never expires, and the call blocks indefinitely.

Parameters:

timeout - the timeout value (in milliseconds)

Returns:

the next message produced for this message consumer, or null if the timeout expires or this message consumer is concurrently closed

Throws:

JMSException - if the Jakarta Messaging provider fails to receive the next message due to some internal error.

receiveNoWait

Message receiveNoWait()
               throws JMSException

Receives the next message if one is immediately available.

Returns:

the next message produced for this message consumer, or null if one is not available

Throws:

JMSException - if the Jakarta Messaging provider fails to receive the next message due to some internal error.

close

void close()
    throws JMSException

Closes the message consumer.

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

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

If this method is called whilst a message listener is in progress in another thread then it will block until the message listener has completed.

This method may be called from a message listener's onMessage method on its own consumer. After this method returns the onMessage method will be allowed to complete normally.

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

Specified by:

close in interface AutoCloseable

Throws:

JMSException - if the Jakarta Messaging provider fails to close the consumer due to some internal error.