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This version is still in development and is not considered stable yet. For the latest stable version, please use Spring AMQP 3.2.0! |
Modifying Messages - Compression and More
A number of extension points exist. They let you perform some processing on a message, either before it is sent to RabbitMQ or immediately after it is received.
As can be seen in Message Converters, one such extension point is in the AmqpTemplate convertAndReceive operations, where you can provide a MessagePostProcessor.
For example, after your POJO has been converted, the MessagePostProcessor lets you set custom headers or properties on the Message.
Starting with version 1.4.2, additional extension points have been added to the RabbitTemplate - setBeforePublishPostProcessors() and setAfterReceivePostProcessors().
The first enables a post processor to run immediately before sending to RabbitMQ.
When using batching (see Batching), this is invoked after the batch is assembled and before the batch is sent.
The second is invoked immediately after a message is received.
These extension points are used for such features as compression and, for this purpose, several MessagePostProcessor implementations are provided.
GZipPostProcessor, ZipPostProcessor and DeflaterPostProcessor compress messages before sending, and GUnzipPostProcessor, UnzipPostProcessor and InflaterPostProcessor decompress received messages.
Starting with version 2.1.5, the GZipPostProcessor can be configured with the copyProperties = true option to make a copy of the original message properties.
By default, these properties are reused for performance reasons, and modified with compression content encoding and the optional MessageProperties.SPRING_AUTO_DECOMPRESS header.
If you retain a reference to the original outbound message, its properties will change as well.
So, if your application retains a copy of an outbound message with these message post processors, consider turning the copyProperties option on.
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Starting with version 2.2.12, you can configure the delimiter that the compressing post processors use between content encoding elements.
With versions 2.2.11 and before, this was hard-coded as :, it is now set to , ` by default.
The decompressors will work with both delimiters.
However, if you publish messages with 2.3 or later and consume with 2.2.11 or earlier, you MUST set the `encodingDelimiter property on the compressor(s) to :.
When your consumers are upgraded to 2.2.11 or later, you can revert to the default of `, `.
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Similarly, the SimpleMessageListenerContainer also has a setAfterReceivePostProcessors() method, letting the decompression be performed after messages are received by the container.
Starting with version 2.1.4, addBeforePublishPostProcessors() and addAfterReceivePostProcessors() have been added to the RabbitTemplate to allow appending new post processors to the list of before publish and after receive post processors respectively.
Also there are methods provided to remove the post processors.
Similarly, AbstractMessageListenerContainer also has addAfterReceivePostProcessors() and removeAfterReceivePostProcessor() methods added.
See the Javadoc of RabbitTemplate and AbstractMessageListenerContainer for more detail.