54 lines
1.9 KiB
Markdown
54 lines
1.9 KiB
Markdown
# Last-Value Queues
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Last-Value queues are special queues which discard any messages when a
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newer message with the same value for a well-defined Last-Value property
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is put in the queue. In other words, a Last-Value queue only retains the
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last value.
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A typical example for Last-Value queue is for stock prices, where you
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are only interested by the latest value for a particular stock.
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## Configuring Last-Value Queues
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Last-value queues are defined in the address-setting configuration:
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<address-setting match="jms.queue.lastValueQueue">
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<last-value-queue>true</last-value-queue>
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</address-setting>
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By default, `last-value-queue` is false. Address wildcards can be used
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to configure Last-Value queues for a set of addresses (see [here](wildcard-syntax.md)).
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## Using Last-Value Property
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The property name used to identify the last value is `"_AMQ_LVQ_NAME"`
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(or the constant `Message.HDR_LAST_VALUE_NAME` from the Core API).
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For example, if two messages with the same value for the Last-Value
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property are sent to a Last-Value queue, only the latest message will be
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kept in the queue:
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``` java
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// send 1st message with Last-Value property set to STOCK_NAME
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TextMessage message = session.createTextMessage("1st message with Last-Value property set");
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message.setStringProperty("_AMQ_LVQ_NAME", "STOCK_NAME");
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producer.send(message);
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// send 2nd message with Last-Value property set to STOCK_NAME
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message = session.createTextMessage("2nd message with Last-Value property set");
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message.setStringProperty("_AMQ_LVQ_NAME", "STOCK_NAME");
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producer.send(message);
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...
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// only the 2nd message will be received: it is the latest with
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// the Last-Value property set
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TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
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System.out.format("Received message: %s\n", messageReceived.getText());
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```
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## Example
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See the [examples](examples.md) chapter for an example which shows how last value queues are configured
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and used with JMS.
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