Meta-annotations

有时，您可能希望对多个侦听器使用相同的配置。为减少样板配置，可以使用元注解创建自己的侦听器注解。以下示例演示了如何执行此操作：

Sometimes you may want to use the same configuration for multiple listeners. To reduce the boilerplate configuration, you can use meta-annotations to create your own listener annotation. The following example shows how to do so:

@Target({ElementType.TYPE, ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@RabbitListener(bindings = @QueueBinding(
        value = @Queue,
        exchange = @Exchange(value = "metaFanout", type = ExchangeTypes.FANOUT)))
public @interface MyAnonFanoutListener {
}

public class MetaListener {

    @MyAnonFanoutListener
    public void handle1(String foo) {
        ...
    }

    @MyAnonFanoutListener
    public void handle2(String foo) {
        ...
    }

}

在上述示例中，由 @MyAnonFanoutListener 注解创建的每个侦听器都会将匿名自动删除队列绑定到扇出交换 metaFanout。从 2.2.3 版本开始，支持 @AliasFor 以允许覆盖元注解注解上的属性。此外，用户注解现在可以是 @Repeatable，从而允许为方法创建多个容器。

In the preceding example, each listener created by the @MyAnonFanoutListener annotation binds an anonymous, auto-delete queue to the fanout exchange, metaFanout. Starting with version 2.2.3, @AliasFor is supported to allow overriding properties on the meta-annotated annotation. Also, user annotations can now be @Repeatable, allowing multiple containers to be created for a method.

@Component
static class MetaAnnotationTestBean {

    @MyListener("queue1")
    @MyListener("queue2")
    public void handleIt(String body) {
    }

}


@RabbitListener
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Repeatable(MyListeners.class)
static @interface MyListener {

    @AliasFor(annotation = RabbitListener.class, attribute = "queues")
    String[] value() default {};

}

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
static @interface MyListeners {

    MyListener[] value();

}