This version is still in development and is not considered stable yet. For the latest stable version, please use Spring AMQP 3.2.0!spring-doc.cn

Message Conversion for Annotated Methods

There are two conversion steps in the pipeline before invoking the listener. The first step uses a MessageConverter to convert the incoming Spring AMQP Message to a Spring-messaging Message. When the target method is invoked, the message payload is converted, if necessary, to the method parameter type.spring-doc.cn

The default MessageConverter for the first step is a Spring AMQP SimpleMessageConverter that handles conversion to String and java.io.Serializable objects. All others remain as a byte[]. In the following discussion, we call this the “message converter”.spring-doc.cn

The default converter for the second step is a GenericMessageConverter, which delegates to a conversion service (an instance of DefaultFormattingConversionService). In the following discussion, we call this the “method argument converter”.spring-doc.cn

To change the message converter, you can add it as a property to the container factory bean. The following example shows how to do so:spring-doc.cn

@Bean
public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() {
    SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
    ...
    factory.setMessageConverter(new Jackson2JsonMessageConverter());
    ...
    return factory;
}

This configures a Jackson2 converter that expects header information to be present to guide the conversion.spring-doc.cn

You can also use a ContentTypeDelegatingMessageConverter, which can handle conversion of different content types.spring-doc.cn

Starting with version 2.3, you can override the factory converter by specifying a bean name in the messageConverter property.spring-doc.cn

@Bean
public Jackson2JsonMessageConverter jsonConverter() {
    return new Jackson2JsonMessageConverter();
}

@RabbitListener(..., messageConverter = "jsonConverter")
public void listen(String in) {
    ...
}

This avoids having to declare a different container factory just to change the converter.spring-doc.cn

In most cases, it is not necessary to customize the method argument converter unless, for example, you want to use a custom ConversionService.spring-doc.cn

In versions prior to 1.6, the type information to convert the JSON had to be provided in message headers, or a custom ClassMapper was required. Starting with version 1.6, if there are no type information headers, the type can be inferred from the target method arguments.spring-doc.cn

This type inference works only for @RabbitListener at the method level.

See Jackson2JsonMessageConverter for more information.spring-doc.cn

If you wish to customize the method argument converter, you can do so as follows:spring-doc.cn

@Configuration
@EnableRabbit
public class AppConfig implements RabbitListenerConfigurer {

    ...

    @Bean
    public DefaultMessageHandlerMethodFactory myHandlerMethodFactory() {
        DefaultMessageHandlerMethodFactory factory = new DefaultMessageHandlerMethodFactory();
        factory.setMessageConverter(new GenericMessageConverter(myConversionService()));
        return factory;
    }

    @Bean
    public DefaultConversionService myConversionService() {
        DefaultConversionService conv = new DefaultConversionService();
        conv.addConverter(mySpecialConverter());
        return conv;
    }

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

    ...

}

For multi-method listeners (see Multi-method Listeners), the method selection is based on the payload of the message after the message conversion. The method argument converter is called only after the method has been selected.