Multi-method Listeners

从版本 1.5.0 开始，你可以在类级别指定 @RabbitListener 注解。这与新的 @RabbitHandler 注解一起使单个侦听器调用不同的方法，具体取决于传入消息的有效负载类型。最好使用示例进行描述：

Starting with version 1.5.0, you can specify the @RabbitListener annotation at the class level. Together with the new @RabbitHandler annotation, this lets a single listener invoke different methods, based on the payload type of the incoming message. This is best described using an example:

@RabbitListener(id="multi", queues = "someQueue")
@SendTo("my.reply.queue")
public class MultiListenerBean {

    @RabbitHandler
    public String thing2(Thing2 thing2) {
        ...
    }

    @RabbitHandler
    public String cat(Cat cat) {
        ...
    }

    @RabbitHandler
    public String hat(@Header("amqp_receivedRoutingKey") String rk, @Payload Hat hat) {
        ...
    }

    @RabbitHandler(isDefault = true)
    public String defaultMethod(Object object) {
        ...
    }

}

在这种情况下，如果转换后的有效负载是 Thing2、Cat 或 Hat，则会调用 @RabbitHandler 方法。您应该明白，系统必须能够根据有效负载类型识别唯一的方法。对类型进行检查，以检验是否可分配给没有注释的单个参数，或者是否注释了 @Payload 注释。请注意，与方法级别 @RabbitListener (described earlier) 中讨论的一样，适用的方法签名是相同的。

In this case, the individual @RabbitHandler methods are invoked if the converted payload is a Thing2, a Cat, or a Hat. You should understand that the system must be able to identify a unique method based on the payload type. The type is checked for assignability to a single parameter that has no annotations or that is annotated with the @Payload annotation. Notice that the same method signatures apply, as discussed in the method-level @RabbitListener (described earlier).

从版本 2.0.3 开始，可以将 @RabbitHandler 方法指定为默认方法，当没有其他方法匹配时，它就会被调用。最多只能指定一个方法。

Starting with version 2.0.3, a @RabbitHandler method can be designated as the default method, which is invoked if there is no match on other methods. At most, one method can be so designated.

@RabbitHandler 仅用于在转换后处理消息有效负载，如果你希望接收未转换的原始 Message 对象，则必须对方法使用 @RabbitListener，而不是类。

@RabbitHandler is intended only for processing message payloads after conversion, if you wish to receive the unconverted raw Message object, you must use @RabbitListener on the method, not the class.