Interface MessageConsumer
- All Superinterfaces:
AutoCloseable
- All Known Subinterfaces:
QueueReceiver
,TopicSubscriber
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
- See Also:
-
Method Summary
Modifier and TypeMethodDescriptionvoid
close()
Closes the message consumer.Gets theMessageConsumer
'sMessageListener
.Gets this message consumer's message selector expression.receive()
Receives the next message produced for this message consumer.receive
(long timeout) Receives the next message that arrives within the specified timeout interval.Receives the next message if one is immediately available.void
setMessageListener
(MessageListener listener) Sets theMessageConsumer
'sMessageListener
.
-
Method Details
-
getMessageSelector
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 JMS provider fails to get the message selector due to some internal error.
-
getMessageListener
Gets theMessageConsumer
'sMessageListener
.This method must not be used in a Java 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 JMS provider fails to get theMessageListener
for one of the following reasons:- an internal error has occurred or
- this method has been called in a Java EE web or EJB application (though it is not guaranteed that an exception is thrown in this case)
- See Also:
-
setMessageListener
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 Java 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 JMS 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 Java EE web or EJB application (though it is not guaranteed that an exception is thrown in this case)
- See Also:
-
receive
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 JMS provider fails to receive the next message due to some internal error.
-
receive
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 JMS provider fails to receive the next message due to some internal error.
-
receiveNoWait
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 JMS provider fails to receive the next message due to some internal error.
-
close
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 JMS provider fails to close the consumer due to some internal error.
-