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Improve Delayer docs around messageGroupId

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* Mention in the Javadocs of the `DelayHandler`, `DelayerEndpointSpec`,
`BaseIntegrationFlowDefinition.delay()`, `GroovyIntegrationFlowDefinition.delay()`,
`KotlinIntegrationFlowDefinition.delay()` that `messageGroupId` is required option
* Explain in the docs why `messageGroupId` is required and why it cannot rely on a bean name
This commit is contained in:
abilan
2023-06-13 10:59:06 -04:00
parent 81af20aabf
commit b5767483e1
6 changed files with 31 additions and 11 deletions
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src/reference/asciidoc/delayer.adoc
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@@ -149,12 +149,16 @@ See <<delayer-release-failures>>.
==== Delayer and a Message Store
The `DelayHandler` persists delayed messages into the message group in the provided `MessageStore`.
(The 'groupId' is based on the required 'id' attribute of the `<delayer>` element.)
(The 'groupId' is based on the required 'id' attribute of the `<delayer>` element.
See also `DelayHandler.setMessageGroupId(String)`.)
A delayed message is removed from the `MessageStore` by the scheduled task immediately before the `DelayHandler` sends the message to the `output-channel`.
If the provided `MessageStore` is persistent (such as `JdbcMessageStore`), it provides the ability to not lose messages on the application shutdown.
After application startup, the `DelayHandler` reads messages from its message group in the `MessageStore` and reschedules them with a delay based on the original arrival time of the message (if the delay is numeric).
For messages where the delay header was a `Date`, that `Date` is used when rescheduling.
If a delayed message remains in the `MessageStore` more than its 'delay', it is sent immediately after startup.
The `messageGroupId` is required and cannot rely on a `DelayHandler` bean name which can be generated.
That way, after application restart, a `DelayHandler` may get a new generated bean name.
Therefore, delayed messages might be lost from rescheduling since their group is not managed by the application anymore.
The `<delayer>` can be enriched with either of two mutually exclusive elements: `<transactional>` and `<advice-chain>`.
The `List` of these AOP advices is applied to the proxied internal `DelayHandler.ReleaseMessageHandler`, which has the responsibility to release the message, after the delay, on a `Thread` of the scheduled task.