Package org.acemq.amqp.api

Interface Step<I,O>

Type Parameters:
I - payload this step receives
O - payload it produces for the next step
Functional Interface:
This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
@FunctionalInterface public interface Step<I,O>
One stage of a pipeline: a message in, the next payload out. 

 class EnrichOrder implements Step<Order, Enriched> {
     public Enriched handle(Message<Order> message) {
         Order order = message.payload();
         return new Enriched(order, customers.lookup(order.customerId()));
     }
 }

Returning the next payload rather than publishing it keeps a step testable — it is a function, and a test calls it — and lets the builder thread types along the chain, so a step that produces an Enriched cannot be put where one producing an Order belongs.

Returning null ends the route for that message. A step that filters is a step that sometimes returns nothing; the message is acknowledged and nothing downstream ever sees it. That is a decision, not a failure, and it is counted separately from both.

A step should be idempotent. Every hop is at-least-once, so a step sees the same message twice whenever a publish succeeds and its acknowledgement does not — configure an idempotency store on the ones where repeating the work would matter.

  • Method Summary

    Modifier and Type
    Method
    Description
    @Nullable O
    handle(Message<I> message)
     

  • Method Details

    • handle

      @Nullable O handle(Message<I> message) throws Exception
      Parameters:
      message - the message to handle
      Returns:
      the payload for the next step, or null to end the route here
      Throws:
      Exception - to fail this step, applying whatever failure policy it was configured with