Spring AMQP：无法结合RabbitTemplate使用ContentTypeDelegatingMessageConverter

核心问题在于RabbitTemplate.convertAndSend()的执行顺序：先调用MessageConverter完成消息转换（此时使用默认空MessageProperties，contentType为octet-stream），再执行MessagePostProcessor设置contentType，导致ContentTypeDelegatingMessageConverter无法根据目标contentType选择对应转换器。

以下是两种可行的解决方案：

方案1：手动调用MessageConverter构造消息后发送 #

直接通过MessageConverter使用指定的contentType构造Message对象，再调用rabbitTemplate.send()发送，确保转换时就能拿到正确的contentType：

@Service
public class RabbitMQService {
    @Autowired
    private RabbitTemplate rabbitTemplate;
    @Autowired
    private MessageConverter messageConverter;

    public void sendMessage(final String exchange, final String routingKey, final Object payload, String contentType, boolean persistent) {
        // 提前构造带正确contentType的MessageProperties
        MessageProperties props = new MessageProperties();
        props.setContentType(contentType);
        props.setDeliveryMode(persistent ? MessageDeliveryMode.PERSISTENT : MessageDeliveryMode.NON_PERSISTENT);
        
        // 用指定属性转换消息
        Message message = messageConverter.toMessage(payload, props);
        rabbitTemplate.send(exchange, routingKey, message);
    }
}

方案2：扩展RabbitTemplate，新增支持传入MessageProperties的重载方法 #

通过扩展RabbitTemplate，添加一个能直接传入MessageProperties的convertAndSend重载方法，让转换阶段就使用指定的属性：

1. 自定义RabbitTemplate子类 #

public class CustomRabbitTemplate extends RabbitTemplate {

    public CustomRabbitTemplate(ConnectionFactory connectionFactory) {
        super(connectionFactory);
    }

    public void convertAndSend(String exchange, String routingKey, Object payload, MessageProperties messageProperties, @Nullable MessagePostProcessor messagePostProcessor) throws AmqpException {
        // 使用传入的MessageProperties进行转换
        Message messageToSend = getRequiredMessageConverter().toMessage(payload, messageProperties);
        if (messagePostProcessor != null) {
            messageToSend = messagePostProcessor.postProcessMessage(messageToSend, null, nullSafeExchange(exchange), nullSafeRoutingKey(routingKey));
        }
        send(exchange, routingKey, messageToSend);
    }
}

2. 替换配置中的RabbitTemplate实例 #

@Bean
public RabbitTemplate rabbitTemplate(final ConnectionFactory connectionFactory,
                                     final Jackson2JsonMessageConverter jsonMessageConverter,
                                     final Jackson2XmlMessageConverter xmlMessageConverter) {
    // 使用自定义的CustomRabbitTemplate
    final var rabbitTemplate = new CustomRabbitTemplate(connectionFactory);
    ContentTypeDelegatingMessageConverter compositeConverter = new ContentTypeDelegatingMessageConverter();
    compositeConverter.addDelegate(MessageProperties.CONTENT_TYPE_JSON, jsonMessageConverter);
    compositeConverter.addDelegate(MessageProperties.CONTENT_TYPE_XML, xmlMessageConverter);
    rabbitTemplate.setMessageConverter(compositeConverter);
    return rabbitTemplate;
}

3. 在服务中调用新方法 #

@Service
public class RabbitMQService {
    @Autowired
    private CustomRabbitTemplate rabbitTemplate;

    public void sendMessage(final String exchange, final String routingKey, final Object payload, String contentType, boolean persistent) {
        MessageProperties props = new MessageProperties();
        props.setContentType(contentType);
        props.setDeliveryMode(persistent ? MessageDeliveryMode.PERSISTENT : MessageDeliveryMode.NON_PERSISTENT);
        // 调用自定义的convertAndSend方法
        rabbitTemplate.convertAndSend(exchange, routingKey, payload, props, null);
    }
}

内容的提问来源于stack exchange，提问作者M.Ricciuti