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Last-Value Queues
Last-Value queues are special queues which discard any messages when a newer message with the same value for a well-defined Last-Value property is put in the queue. In other words, a Last-Value queue only retains the last value.
A typical example for Last-Value queue is for stock prices, where you are only interested by the latest value for a particular stock.
Configuration
Last-Value queues can be statically configured via the last-value
boolean property:
<address name="foo.bar">
<multicast>
<queue name="orders1" last-value="true"/>
</multicast>
</address>
Specified on creating a queue by using the CORE api specifying the parameter
lastValue to true.
Or on auto-create when using the JMS Client by using address parameters when creating the destination used by the consumer.
Queue queue = session.createQueue("my.destination.name?last-value=true");
Topic topic = session.createTopic("my.destination.name?last-value=true");
Also the default for all queues under and address can be defaulted using the
address-setting configuration:
<address-setting match="lastValueQueue">
<default-last-value-queue>true</default-last-value-queue>
</address-setting>
By default, default-last-value-queue is false.
Address wildcards can be used to configure Last-Value queues
for a set of addresses (see here).
Note that address-setting last-value-queue config is deprecated, please use
default-last-value-queue instead.
Last-Value Property
The property name used to identify the last value is "_AMQ_LVQ_NAME"
(or the constant Message.HDR_LAST_VALUE_NAME from the Core API).
For example, if two messages with the same value for the Last-Value property are sent to a Last-Value queue, only the latest message will be kept in the queue:
// send 1st message with Last-Value property set to STOCK_NAME
TextMessage message = session.createTextMessage("1st message with Last-Value property set");
message.setStringProperty("_AMQ_LVQ_NAME", "STOCK_NAME");
producer.send(message);
// send 2nd message with Last-Value property set to STOCK_NAME
message = session.createTextMessage("2nd message with Last-Value property set");
message.setStringProperty("_AMQ_LVQ_NAME", "STOCK_NAME");
producer.send(message);
...
// only the 2nd message will be received: it is the latest with
// the Last-Value property set
TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
System.out.format("Received message: %s\n", messageReceived.getText());
Example
See the last-value queue example which shows how last value queues are configured and used with JMS.