# API Documentation: MQ Activiti Extension: `mqSubscribeReplyDelegate`

*Author*: [brian@inteligr8.com](mailto:brian@inteligr8.com)
*Since Version*: 1.0


This method listens for a reply message on an MQ queue.

The process instance will block until a corresponding reply message is received.  It uses the `mq_correlationId` variable to select the corresponding reply message.  That variable is automatically set by the `mqPublishDelegate` task.  This is meant to be used after `mqPublishDelegate` and not just by itself.  If you want to start processes with an MQ subscription see the `mqSubscribeDelegate` task.

If you have more than one MQ communication in a single process, set the `mq_messageName` field on this and the corresponding `mqPublishDelegate` task.  The resultant variables will then include that message name (e.g. `mq_messageId_{mq_messageName}`).

This requires a long running connection to MQ.  It runs in a long running Activiti job/execution.  If there is a failure or the server is restarted, the Activiti job will fail and automatically retry per the Activiti standard features.  After exhausting retries, it may eventually dead-letter.  Retry the job to continue the subscription.

*See Also*: [`mqPublishDelegate`](bean-mqPublishDelegate.md)
*See Also*: [`mqSubscribeDelegate`](bean-mqSubscribeDelegate.md)

## <a name="delegate"></a> Delegate Expression Uses

This bean may be used as a *Delegate* using the "Delegate Expression" field as shown in the snippet below.

```javascript
${mqSubscribeReplyDelegate}
```

You may use it in a **Service Task**.


This method makes this bean an Activiti delegate.

| Input Type               | Name                     | Java Type                                        | Documentation                      |
| ------------------------ | ------------------------ | ------------------------------------------------ | ---------------------------------- |
| BPMN Field               | `mq_connectorId`         |                                                  | An Activiti App Tenant Endpoint ID or Java system property in the format `inteligr8.mq.connectors.{connectorId}.url`.  Using system properties support `url`, `username`, and `password`. |
| BPMN Field               | `mq_queueName`           |                                                  | The name of an MQ destination (queue or topic).  This is the target of the message.  If it doesn't exist, it will be created. |
| BPMN Field               | `mq_metadataProcessScope` |                                                  | [optional] `true` to set all Activiti result variables in the process instance scope; otherwise the variables will be local to the task. |
| BPMN Field               | `mq_messageName`         |                                                  | [optional] A unique identifier to append to Activiti result variable names when more than one MQ message publication/subscription is supported by a process. |
| Activiti Variable        | `mq_correlationId`       |                                                  | The correlating identifier of the message to receive.  Used to correlate between sent/received messages; like a thread of communication. |

| Result Type              | Java Type, Name, or Error Code                   | Documentation                    |
| ------------------------ | ------------------------------------------------ | -------------------------------- |
| Activiti Variable        | `mq_messageId`                                   | The unique message identifer of the message received. |
| Activiti Variable        | `mq_deliveryTime`                                | The time the message was delivered; not received.  It is of the `java.util.Date` type as supported by Activiti. |
| Activiti Variable        | `mq_priority`                                    | An integer priority of the message; value depends on MQ protocol. |
| Activiti Variable        | `mq_payload`                                     | The body of the MQ message.  May include expressions.  May be `null`. |
| Activiti Variable        | `mq_payloadMimeType`                             | The MIME type of the body of the MQ message.  May be `null`. |
| Activiti Variable        | `mq_replyQueueName`                              | The name of an MQ destination (queue or topic) to use to reply to the received message.  The reply message must have the same correlating identifier.  May be `null`. |
| Activiti Variable        | `mq_statusQueueName`                             | The name of an MQ destination (queue or topic) to use to reply to the received message.  The reply message must have the same correlating identifier.  May be `null`. |
| Thrown BPMN Error        | `correlation`                                    | `mq_correlationId` is required.  |
| Thrown BPMN Error        | `timeout`                                        | The MQ connection timed out connecting or waiting for a message. |
| Thrown BPMN Error        | `network`                                        | The MQ connection experienced network issues. |
| Thrown BPMN Error        | `mq`                                             | An unknown MQ issue occurred.    |

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