Apache Camel - How to trigger Compensation Handler? (7/250-2016)

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Compensation handler in camel is based on the concept of Unit of Work — group together multiple tasks as a single unit — mimicking transnational boundaries.

• org.apache.camel.spi.UnitOfWork Interface represents UnitOfWork in Camel.
• Exchange has exactly one UnitOfWork (private to Exchange — not shared with others) — accessed from exchange using method — getUnitOfWork
• Camel will automatically inject a new UnitOfWork into Exchange — using internal processor UnitOfWorkProcessor — involved in start of every route
• At the end of the route, the processor invokes registered Synchronization callback

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Synchronization (a callback)

• org.apache.camel.spi.Synchronization Interface is used to represent Synchronization.
• used to execute custom logic — after processing — using the methods below.

onComplete
onFailure

• An exchange can add multiple callBacks.
• If there is an error while processing callBack — Camel will log in WARN level and continue to next callback.

Synchronization is added / removed to the UnitOfWork using the methods below — using a processor.

addSynchronization
removeSynchronization
done — invoked when UnitOfWork is complete

OR

addOnCompletetion

This is a method on the exchange — it creates a new thread — and is the preferred method for compensation handling.

addOnCompletion can be written in Java DSL as well as Spring DSL.
It can be route / context scoped.

References: