To Consume JMS Messages
The Consume operation in the JMS connector provides ability to consume a Message at any given time of the flow, from any given Destination.
The syntax to consume a message from a Queue is:
<jms:consume config-ref="JMS_config" destination="#[vars.destination]"/>
The operation above consumes the first available message in the Queue identified by the destination, and then converts it to a
MuleMessage resulting in the following structure:
The message’s content as payload.
The message’s metadata in the message attributes.
Once received, the Message will be immediately ACKed by default. If you want to control the ACK of the Message after some processing, then
ackMode should be set to
For more information regarding a Message ACK, check the How To Handle Message Acknowledgement.
By default, the maximum wait time is configured in 10 seconds, producing a
JMS:TIMEOUT error if no message is available in that period.
If order to configure a timeout that fits better your use case, customize the
In order to wait indefinitely for a Message to arrive, the
maximumWait value has to be set to
-1. In this case, no
TIMEOUT error will be thrown.
When polling for a Message with a certain frequency, you don’t want the consumer to block waiting for the Message, but instead just try to consume it if one is present.
In this cases, the
maximumWait can be set to
0, indicating that no waiting should occur, and neither a
JMS:TIMEOUT should be thrown if no Message is available in the destination.
The output of the
consume operation will be
null when no Message is present for consumption and no error is thrown.
The JMS connector provides full support for filtering which Messages should be consumed based on the standard JMS selector language.
For example, if you have a priority Queue with Messages that need to be processed faster than the others, we can do:
<jms:consume config-ref="JMS_config" destination="openTickets" selector="JMSPriority=8"/>
When a selector is configured, only the Messages matching it will be received, ignoring if any other Message is in the destination.
The JMS Connector does its best to auto determine a Message’s mime type (
contentType) based on the
MM_MESSAGE_CONTENT_TYPE property. However, there are cases in which that best guess is not enough, and you need first-hand knowledge of the Message’s content.
In such cases, you can force that content type to a particular value by using the
The same process works for encoding. By default, the connector will assume that the runtime’s default encoding matches the one in the Message if no other information is provided. You can set this by using the
Consuming messages from a Topic destination is very similar to consuming them from a Queue, but with the extra functionality of being able to use Topic subscriptions to share state between consumers. The syntax for consuming messages from a Topic is:
<jms:consume config-ref="JMS_config" destination="#[vars.destination]"> <jms:consumer-type> <jms:topic-consumer/> </jms:consumer-type> </jms:consume>
consume operation parameters remain the same, but now you can handle the subscription configuration in the
For details on how to configure the Topic subscriptions go to Using Topic Subscriptions.
As stated before, each Message received will consist of two parts:
The payload, containing the content of the Message
The attributes, containing metadata regarding the Message
This Metadata has three parts that map all the information available in a JMS Message:
Check the JMS Reference for details about the Attributes structure.