Chapter 15. Filter Expressions and Message Selectors

The messaging-activemq subsystem in JBoss EAP provides a powerful filter language based on a subset of the SQL 92 expression syntax.

It is the same as the syntax used for JMS selectors, but the predefined identifiers are different. For documentation on JMS selector syntax, refer to the JEE 7 Javadoc for javax.jms.Message.

The filter attribute can be found in several places within the configuration.

Predefined Queues. When pre-defining a queue, a filter expression can be defined for it. Only messages that match the filter expression will enter the queue. The configuration snippet below shows a queue definition that includes a filter:
```
  <subsystem xmlns="urn:jboss:domain:messaging-activemq:1.0">
    ...
    <queue
      name="myQueue"
      filter="<FILTER_EXPRESSION>"
      ...
    />
    ...
  </subsystem>
```
To create queue with a selector in the management CLI you would use something like following command:
```
jms-queue add --queue-address=<QUEUE_ADDRESS> --selector=<FILTER_EXPRESSION>
```
Core bridges can be defined with an optional filter expression, only matching messages will be bridged. Below is a snippet from a sample configuration file where the messaging-activemq subsystem includes a bridge with a filter.
```
 <subsystem xmlns="urn:jboss:domain:messaging-activemq:1.0">
    ...
    <bridge
      name="myBridge"
      filter="<FILTER_EXPRESSION>"
      ...
    />
    ...
  </subsystem>
```
Diverts can be defined with an optional filter expression, only matching messages will be diverted. See Diverts for more information. The example snippet below shows a Divert using a filter:
```
  <subsystem xmlns="urn:jboss:domain:messaging-activemq:1.0">
    ...
    <divert
      name="myDivert"
      filter="<FILTER_EXPRESSION>"
      ...
    />
    ...
  </subsystem>
```

There are some differences between JMS selector expressions and JBoss EAP messaging core filter expressions. Whereas JMS selector expressions operate on a JMS message, JBoss EAP messaging core filter expressions operate on a core message.

The following identifiers can be used in core filter expressions to refer to the attributes of a core message:

AMQPriority. To refer to the priority of a message. Message priorities are integers with valid values from 0 - 9. 0 is the lowest priority and 9 is the highest. E.g. AMQPriority = 3 AND animal = 'aardvark'
AMQExpiration. To refer to the expiration time of a message. The value is a long integer.
AMQDurable. To refer to whether a message is durable or not. The value is a string with valid values: DURABLE or NON_DURABLE.
AMQTimestamp. The timestamp of when the message was created. The value is a long integer.
AMQSize. The size of a message in bytes. The value is an integer.

Any other identifiers used in core filter expressions will be assumed to be properties of the message.

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Chapter 15. Filter Expressions and Message Selectors

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