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  * Copyright (c) 2010-2011. Axon Framework
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
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 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.
package org.axonframework.eventhandling.annotation;
Annotation to be placed on methods that can handle events.

Annotated methods must comply to a few simple rules:

For each event, only a single method will be invoked per object instance with annotated methods. This method is resolved in the following order:

  1. First, the event handler methods of the actual class (at runtime) are searched
  2. If a method is found with a parameter that the domain event can be assigned to, it is marked as eligible
  3. After a class has been evaluated (but before any super class), the most specific event handler method is called. That means that if an event handler for a class A and one for a class B are eligible, and B is a subclass of A, then the method with a parameter of type B will be chosen
  4. If no method is found in the actual class, its super class is evaluated.
  5. If still no method is found, the event listener ignores the event

If you do not want any events to be ignored, but rather have some logging of the fact that an unhandled event came by, make an abstract superclass that contains an event handler method that accepts org.axonframework.domain.DomainEvent.

Note: if there are two event handler methods accepting the same argument, the behavior is undefined.

Allard Buijze
See also:
public @interface EventHandler {
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