To Consume IBM MQ Messages

The Consume operation in the IBM MQ connector provides the ability to consume a message at any given time of the flow, from any given Destination.

Consuming a Message

The syntax to consume a message from a queue is:

<ibm-mq:consume config-ref="IBM_MQ_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 Mule Message resulting in the following structure:

The message’s content as the payload.
The message’s metadata in the message attributes.

Once received, the message is immediately acknowledged by default. If you want to control the ACK of the message after some processing, then set ackMode to MANUAL. For more information regarding a Message ACK, see Handling Message Acknowledgment.

Waiting for a Message

By default, the maximum wait time is configured to 10 seconds, producing a IBM-MQ:TIMEOUT error if no message is available in that period. To configure a timeout that fits better your use case, customize the maximumWait and maximumWaitUnit parameters.

To wait indefinitely for a message to arrive, the maximumWait value has to be set to -1. In this case, no TIMEOUT error is thrown.

Filtering Incoming Messages

The IBM MQ 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:

<ibm-mq:consume config-ref="IBM_MQ_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.

MIME Types and Encoding

The IBM MQ Connector does its best to automatically 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 contentType parameter.

The same process works for encoding. By default, the connector assumes that the Mule runtime’s default encoding matches the one in the message if no other information is provided. You can set this by using the encoding parameter.

This MIME type propagation only works when the IBM MQ Target Client is selected as JMS_COMPLIANT.

Consuming a Message Using Topic Subscriptions

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:

<ibm-mq:consume config-ref="IBM_MQ_config" destination="#[vars.destination]">
    <ibm-mq:consumer-type>
        <ibm-mq:topic-consumer/>
    </ibm-mq:consumer-type>
</ibm-mq:consume>

All the consume operation parameters remain the same, but now you can handle the subscription configuration in the topic-consumer parameter.

For details on how to configure the topic subscriptions see Using Topic Subscriptions.

Incoming Message Metadata

Each received message consists of two parts:

Payload: The content of the message.
Attributes: The metadata regarding the message.

This metadata has three parts that map all the information available in a JMS message:

AckId
Headers
Properties

See JMS Reference for details regarding the attributes structure.