如何在 RabbitMQ 消息上添加 x-delay header？

Question

I'm trying to add a header x-delay on my messages using a instance of MessagePostProcessor but it gives me an exception saying:

java.lang.UnsupportedOperationException: MessageHeaders is immutable

import org.springframework.messaging.Message
import org.springframework.messaging.core.MessagePostProcessor
import org.springframework.stereotype.Component

@Component
class AmpqRoutingKeyStrategy {

    private static CUSTOM_DELAY = 120000

    MessagePostProcessor get() {
        return withDelay(CUSTOM_DELAY)
    }

    static MessagePostProcessor withDelay(Integer milliSeconds) {
        return new MessagePostProcessor() {
            @Override
            Message postProcessMessage(Message message) {
                message.getHeaders().put('x-delay', milliSeconds)
                return message
            }
        }
    }
}

The example above is used in many articles about this topic, I know that we have the option to add the x-delay header but how can I do it without raising this exception?

Answer 1

The documentation says:

IMPORTANT: This class is immutable. Any mutating operation such as put(..), putAll(..) and others will throw UnsupportedOperationException.

The solution is to recreate the message:

static MessagePostProcessor withDelay(Integer milliSeconds) {
    return new MessagePostProcessor() {
        @Override
        Message postProcessMessage(Message message) {
            return org.springframework.messaging.support.MessageBuilder
                .fromMessage(message)
                .setHeader("x-delay", milliseconds)
                .build()
        }
    }
}