Delayed Message Exchange
Spring AMQP 支持 RabbitMQ 延迟消息交换插件：https://docs.spring.io/spring-amqp/reference/html/#delayed-message-exchange。对于入站消息，x-delay 头映射到 AmqpHeaders.RECEIVED_DELAY 头。设置 AMQPHeaders.DELAY 头会导致在出站消息中设置相应的 x-delay 头。你还可以指定出站端点上的 delay 和 delayExpression 属性（使用 XML 配置时为 delay-expression）。这些属性优先于 AmqpHeaders.DELAY 头。
Spring AMQP supports the RabbitMQ Delayed Message Exchange Plugin.
For inbound messages, the x-delay header is mapped to the AmqpHeaders.RECEIVED_DELAY header.
Setting the AMQPHeaders.DELAY header causes the corresponding x-delay header to be set in outbound messages.
You can also specify the delay and delayExpression properties on outbound endpoints (delay-expression when using XML configuration).
These properties take precedence over the AmqpHeaders.DELAY header.