You seem to have already found out about the proper way to use but I’d like to go into some of the details here a bit for others to find as well. I went into similar detail about PagedResourceAssembler
in this answer.
Representation models
Spring HATEOAS ships with a variety of base classes for representation models that make it easy to create representations equipped with links. There are three types of classes provided out of the box:
Resource
– an item resource. Effectively to wrap around some DTO or entity that captures a single item and enriches it with links.Resources
– a collection resource, that can be a collection of somethings but usually are a collection ofResource
instances.PagedResources
– an extension ofResources
that captures additional pagination information like the number of total pages etc.
All of these classes derive from ResourceSupport
, which is a basic container for Link
instances.
Resource assemblers
A ResourceAssembler
is now the mitigating component to convert your domain objects or DTOs into such resource instances. The important part here is, that it turns one source object into one target object.
So the PagedResourcesAssembler
will take a Spring Data Page
instance and transform it into a PagedResources
instance by evaluating the Page
and creating the necessary PageMetadata
as well as the prev
and next
links to navigate the pages. By default – and this is probably the interesting part here – it will use a plain SimplePagedResourceAssembler
(an inner class of PRA
) to transform the individual elements of the page into nested Resource
instances.
To allow to customize this, PRA
has additional toResource(…)
methods that take a delegate ResourceAssembler
to process the individual items. So you end up with something like this:
class UserResource extends ResourceSupport { … }
class UserResourceAssembler extends ResourceAssemblerSupport<User, UserResource> { … }
And the client code now looking something like this:
PagedResourcesAssembler<User> parAssembler = … // obtain via DI
UserResourceAssembler userResourceAssembler = … // obtain via DI
Page<User> users = userRepository.findAll(new PageRequest(0, 10));
// Tell PAR to use the user assembler for individual items.
PagedResources<UserResource> pagedUserResource = parAssembler.toResource(
users, userResourceAssembler);
Outlook
As of the upcoming Spring Data Commons 1.7 RC1 (and Spring HATEOAS 0.9 transitively) the prev
and next
links will be generated as RFC6540 compliant URI templates to expose the pagination request parameters configured in the HandlerMethodArgumentResolvers
for Pageable
and Sort
.
The configuration you’ve shown above can be simplified by annotating the config class with @EnableSpringDataWebSupport
which would let you get rid off all the explicit bean declarations.