spring-how-to-customise-argument-resolution.md

Spring - Customising Argument Resolution

This library uses any Jackson ObjectMapper bean present in the application to de-serialise the message payloads. If the application is a Spring Boot Web application it will use the default ObjectMapper provided by the JacksonAutoConfiguration. This guide provides steps to provide a custom ObjectMapper, as well as how to customise the types of ArgumentResolvers being used.

Providing your own ObjectMapper

To override the default ObjectMapper being used, you must supply your own SqsListenerObjectMapperSupplier that will provide the ObjectMapper.

@Configuration
public class MyConfiguration {

    @Bean
    public SqsListenerObjectMapperSupplier objectMapperSupplier() {
        return () -> new ObjectMapper();
    }
}

The reason for this supplier being created, instead of defining your own ObjectMapper bean is to reduce complexity of interoperability with the existing ObjectMappers, like the Spring Boot auto configured ObjectMapper used for HTTP serialisation and de-serialisation.

Providing your own ArgumentResolverService

If you want to customise the entire argument resolution process, you can provide your own ArgumentResolverService. This can be useful if you only want to support certain argument resolutions or want to have control on how you resolve arguments.

@Configuration
public class MyConfiguration {

    @Bean
    public ArgumentResolverService argumentResolverService(final SqsListenerObjectMapperSupplier objectMapperSupplier) {
        final ObjectMapper objectMapper = objectMapperSupplier.get();
        final List<ArgumentResolver<?>> argumentResolvers = Arrays.asList(
            new PayloadArgumentResolver(new JacksonPayloadMapper(objectMapper)),
            new MessageAttributeArgumentResolver(objectMapper),
            new MessageArgumentResolver()
        );
        return new DelegatingArgumentResolverService(argumentResolvers);
    }
}

Overwriting core ArgumentResolvers that use Jackson's ObjectMapper

If you want to override the ArgumentResolvers that use an ObjectMapper, you can supply those resolvers as beans to auto configure them into the default ArgumentResolverService.

@Configuration
public class MyConfiguration {

    private static final ObjectMapper MY_OBJECT_MAPPER_FOR_SQS = new ObjectMapper();

    @Bean
    public PayloadArgumentResolver payloadArgumentResolver() {
        return new PayloadArgumentResolver(new JacksonPayloadMapper(MY_OBJECT_MAPPER_FOR_SQS));
    }

    @Bean
    public MessageAttributeArgumentResolver messageAttributeArgumentResolver() {
        return new MessageAttributeArgumentResolver(MY_OBJECT_MAPPER_FOR_SQS);
    }
}

De-serialising without using Jackson

To use a different de-serialisation tool, like gson, you can implement a custom PayloadMapper and build the PayloadArgumentResolver like in the above example.