Annotated Endpoint Method Signature

到目前为止，我们已经向端点中注入了一个简单的 String，但它实际上可以具有一个非常灵活的方法签名。以下示例对其进行了重新编写，以使用自定义头注入 Order：

So far, we have been injecting a simple String in our endpoint, but it can actually have a very flexible method signature. The following example rewrites it to inject the Order with a custom header:

@Component
public class MyService {

    @RabbitListener(queues = "myQueue")
    public void processOrder(Order order, @Header("order_type") String orderType) {
        ...
    }
}

以下列表显示了可与侦听器端点中的参数匹配的参数：

The following list shows the arguments that are available to be matched with parameters in listener endpoints:

The raw org.springframework.amqp.core.Message.
The MessageProperties from the raw Message.
The com.rabbitmq.client.Channel on which the message was received.
The org.springframework.messaging.Message converted from the incoming AMQP message.
@Header-annotated method arguments to extract a specific header value, including standard AMQP headers.
@Headers-annotated argument that must also be assignable to java.util.Map for getting access to all headers.
The converted payload

未带注解且不是受支持类型之一（即 Message、MessageProperties、Message<?> 和 Channel）的元素与有效负载匹配。你可以通过使用 @Payload 为参数添加注解，使其显式。你还可以通过添加额外的 @Valid 开启验证。

A non-annotated element that is not one of the supported types (that is, Message, MessageProperties, Message<?> and Channel) is matched with the payload. You can make that explicit by annotating the parameter with @Payload. You can also turn on validation by adding an extra @Valid.

注入 Spring 的消息抽象的功能非常有用，可以从 transport 特定的消息中存储的所有信息中受益，而无需依赖 transport 特定的 API。以下示例显示如何实现：

The ability to inject Spring’s message abstraction is particularly useful to benefit from all the information stored in the transport-specific message without relying on the transport-specific API. The following example shows how to do so:

@RabbitListener(queues = "myQueue")
public void processOrder(Message<Order> order) { ...
}

方法参数的处理由 DefaultMessageHandlerMethodFactory 提供，你可以进一步对其进行自定义以支持其他方法参数。转换和验证支持也可以在那里进行自定义。

Handling of method arguments is provided by DefaultMessageHandlerMethodFactory, which you can further customize to support additional method arguments. The conversion and validation support can be customized there as well.

例如，如果我们希望在处理之前确保我们的 Order 有效，我们可以用 @Valid 为有效负载添加注解，并配置必要的验证器，如下所示：

For instance, if we want to make sure our Order is valid before processing it, we can annotate the payload with @Valid and configure the necessary validator, as follows:

@Configuration
@EnableRabbit
public class AppConfig implements RabbitListenerConfigurer {

    @Override
    public void configureRabbitListeners(RabbitListenerEndpointRegistrar registrar) {
        registrar.setMessageHandlerMethodFactory(myHandlerMethodFactory());
    }

    @Bean
    public DefaultMessageHandlerMethodFactory myHandlerMethodFactory() {
        DefaultMessageHandlerMethodFactory factory = new DefaultMessageHandlerMethodFactory();
        factory.setValidator(myValidator());
        return factory;
    }
}