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- All Superinterfaces:
AutoCloseable
- All Known Subinterfaces:
QueueReceiver
,TopicSubscriber
public interface MessageConsumer extends AutoCloseable
A client uses aMessageConsumer
object to receive messages from a destination. AMessageConsumer
object is created by passing aDestination
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 theMessageConsumer
asynchronously deliver them as they arrive.For synchronous receipt, a client can request the next message from a
MessageConsumer
using one of itsreceive
methods. There are several variations ofreceive
that allow a client to poll or wait for the next message.For asynchronous delivery, a client can register a
MessageListener
object with aMessageConsumer
. As messages arrive at theMessageConsumer
, it delivers them by calling theMessageListener
'sonMessage
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
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description void
close()
Closes the message consumer.MessageListener
getMessageListener()
Gets theMessageConsumer
'sMessageListener
.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 theMessageConsumer
'sMessageListener
.
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Method Detail
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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.
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getMessageListener
MessageListener getMessageListener() throws JMSException
Gets theMessageConsumer
'sMessageListener
.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
'sMessageListener
, or null if one was not set - Throws:
JMSException
- if the Jakarta Messaging provider fails to get theMessageListener
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)
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setMessageListener
void setMessageListener(MessageListener listener) throws JMSException
Sets theMessageConsumer
'sMessageListener
.Setting the the
MessageListener
to null is the equivalent of unsetting theMessageListener
for theMessageConsumer
.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 theMessageConsumer
'sMessageListener
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()
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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.
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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.
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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.
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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 blockedreceive
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 theonMessage
method will be allowed to complete normally.This method is the only
MessageConsumer
method that can be called concurrently.- Specified by:
close
in interfaceAutoCloseable
- Throws:
JMSException
- if the Jakarta Messaging provider fails to close the consumer due to some internal error.
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