Compatibility with Spring HATEOAS 0.19.0.RELEASE

[wilkinsona]

Investigate removing direct use of HalHandlerInstantiator in favour of customisation applied by Jackson2ModuleRegisteringBeanPostProcessor

[wilkinsona]

@olivergierke described Jackson2ModuleRegisteringBeanPostProcessor as:

It tweaks all MappingJackson2HttpMessageConverter contained in RequestMappingHandlerAdapters, AnnotationMethodHandlerAdapters and RestTemplates to get the Jackson2HalModule registered with the _halObjectMapper

As far as I can tell, that's not what happens in the RequestMappingHandlerAdapter case at least. Instead of registering the module with the ObjectMapper of all existing MappingJackson2HttpMessageConverters it adds a new MappingJackson2HttpMessageConverter, with an ObjectMapper that is configured with the module, to the start of the list . However, this new converter is only configured to support application/hal+json. This means that the converter doesn't handle requests that accept application/json and one of the converters later in the list with an ObjectMapper that doesn't have the module registered is used instead.

The above means that the work done by Jackson2ModuleRegisteringBeanPostProcessor is insufficient as a fix for #2147 which requires a request that accepts application/json to get a HAL-formatted response when Spring HATEOAS is being used.

[gregturn]

I tweaked the order of things and pushed it to a branch at https://github.com/gregturn/spring-boot/tree/gh-3882.

mvn clean install passed all the tests, so if there is some lingering issue, its not trapped by the tests.

[wilkinsona]

Unless I missed it, that branch doesn't contain the ordering change. Also, as I explained on Slack, I don't think it's a good solution:

That will have almost certainly broken something else. You've switched off the ObjectMapper created by JacksonAutoConfiguration as it's @ConditionalOnMissingBean(ObjectMapper.class) and HypermediaAutoConfiguration will have created the HAL one before JacksonAutoConfiguration runs. Among other things, that means there's now no @Primary ObjectMapper in the context.

[gregturn]

I fixed the branch (had accidentally pushed the mod to spring-projects again), but feel free to shoot the patch or drop it all together.

[wilkinsona]

@olivergierke and I have discussed this. We came to the conclusion that there's nothing that we should do in Spring Boot 1.2.x. I have opened #3891 to improve things in 1.3 where we can make the broader changes that I think may be necessary.

Users of Spring Boot 1.2.x and Spring Data REST that want to use Spring Data Gosling can safely do so if they also upgrade Spring HATEOAS to 0.19.0.RELEASE. This is because the auto-configuration of Spring Data REST switches off the auto-configuration for Spring HATEOAS that's incompatible with Spring HATEOAS 0.19.0.RELEASE

Users of Spring Boot 1.2.x that want to use Spring HATEOAS on its own should stick with the version that's provided by Spring Boot's dependency management.