`IndexOutOfBoundException` if no media type configurations registered

[EarthCitizen]

Our application needs to create a RestTemplate bean unrelated to HATEOAS:

@Bean
public RestTemplate restTemplate() {
    return new RestTemplate();
}

But spring-hateoas is interfering with this bean unexpectedly and unwantedly:

Caused by: java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0
	at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64) ~[na:na]
	at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70) ~[na:na]
	at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:266) ~[na:na]
	at java.base/java.util.Objects.checkIndex(Objects.java:359) ~[na:na]
	at java.base/java.util.ArrayList.get(ArrayList.java:427) ~[na:na]
	at org.springframework.hateoas.config.WebConverters.augment(WebConverters.java:121) ~[spring-hateoas-1.3.3.jar:1.3.3]
	at org.springframework.hateoas.config.WebConverters.augmentClient(WebConverters.java:87) ~[spring-hateoas-1.3.3.jar:1.3.3]
	at org.springframework.hateoas.config.HypermediaRestTemplateConfigurer.registerHypermediaTypes(HypermediaRestTemplateConfigurer.java:47) ~[spring-hateoas-1.3.3.jar:1.3.3]
	at org.springframework.hateoas.config.RestTemplateHateoasConfiguration$HypermediaRestTemplateBeanPostProcessor.postProcessBeforeInitialization(RestTemplateHateoasConfiguration.java:73) ~[spring-hateoas-1.3.3.jar:1.3.3]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:422) ~[spring-beans-5.3.9.jar:5.3.9]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1778) ~[spring-beans-5.3.9.jar:5.3.9]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:602) ~[spring-beans-5.3.9.jar:5.3.9]
	... 113 common frames omitted

When looking at WebConverters.augment(WebConverters.java:121), I find this:

Class<?> rootType = infos.get(0).getRootType();

Our application needs to disable all provided forms HypermediaMappingInformation to disable their ObjectMapper mixins, and is doing the following to do that:

@EnableHypermediaSupport(type = {})

It would seem that spring-hateoas makes the incorrect assumption that there will always be at least one HypermediaMappingInformation defined, despite making it possible to define none.

[odrotbohm]

While this is obviously a bug, I'd love to learn more about the arrangement. Not enabling any media types in @EHS doesn't mean the list will have to be empty. The attribute only selects which media types of the ones shipping with Spring HATEOAS to activate. There still might be custom ones registered as simple configuration classes. While it's theoretically possible, I wonder what kind of use you make of Spring HATEOAS, if you're not actually rendering a hypermedia type in the first place.

[EarthCitizen]

@odrotbohm In a nutshell, I am using link building, but all of the Jackson mixins and ObjectMapper customized settings provided by this library, in my case, need to be discarded. I have requirements for which those things interfere, and I need to use my own mixins for PageModel and CollectionModel. And I am fine setting this up in the global ObjectMapper. In my case, I don't need an ObjectMapper that is specific to one use case.

Initially, I was able to do this with setting @EnableHypermediaSupport(type = {}), and this worked until we added a RestTemplate bean.

I am currently able to work around the problem by implementing a HypermediaMappingInformation that returns JSON for the media type, and the same ObjectMapper that is given to it without making modifications.

[odrotbohm]

Doesn't that mean that you're essentially using a representation format that's just the standard Jackson rendering of our RepresentationModel? Please note, that this is completely unsupported in the way that we allow ourselves to change that structure at will, i.e. the JSON you get from rendering them as-is might change any time. I can only strongly recommend to stick to a well-defined hypermedia format.

[EarthCitizen]

@odrotbohm No, I am not using the standard Jackson rendering. I am registering custom mixins for PageModel, CollectionModel, and EntityModel. None of the built-in formats allow me to render those in the standard stipulated by my company.

[odrotbohm]

That's great to hear. I wonder if it makes sense to register the customizations via a HypermediaMappingInformation bean.