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Chapter 12. Filter Expressions
HornetQ 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.
Filter expressions are used in several places in HornetQ.
- Predefined Queues. When pre-defining a queue, either in
<JBOSS_HOME>/jboss-as/server/<PROFILE>/deploy/hornetq/hornetq-configuration.xmlorJBOSS_DIST/jboss-as/server/<PROFILE>/deploy/hornetq/hornetq-jms.xmla filter expression can be defined for a queue. Only messages that match the filter expression will enter the queue. - Core bridges can be defined with an optional filter expression, only matching messages will be bridged (see Chapter 34, Core Bridges).
- Diverts can be defined with an optional filter expression. Only matching messages will be diverted (see Chapter 33, Diverting and Splitting Message Flows).
- Filters are also used programmatically when creating consumers, queues and in several places as described in Chapter 28, Management.
There are some differences between JMS selector expressions and HornetQ core filter expressions. Whereas JMS selector expressions operate on a JMS message, HornetQ core filter expressions operate on a core message.
The following identifiers can be used in a core filter expression to refer to attributes of the core message in an expression:
- HQPriority
- To refer to the priority of a message. Message priorities are integers with valid values from
0 - 9.0is the lowest priority and9is the highest. For example,HQPriority = 3 and department = 'payroll'. This refers to a message with a priority of three and a department of 'payroll'. - HQExpiration
- To refer to the expiration time of a message. The value is a long integer.
- HQDurable
- To refer to whether a message is durable or not. The value is a string with valid values:
DURABLEorNON_DURABLE. - HQTimestamp
- The time stamp of when the message was created. The value is a long integer.
- HQSize
- 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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