Add support for specifying array serialization for a particular link relation

This is a follow-up on #288, as suggested in last comment on that issue.

We’re including item link relation (see https://tools.ietf.org/html/rfc6573#section-2.1) to _links in our HAL responses that return collections/pages.

The code that handles this in @Controller handler method looks something like this:

for (MyResource resource : resources) { // resources is an instance of PagedResources
    resources.add(resource.getLink(Link.REL_SELF).withRel("item"));
}

This works fine when actually there are multiple resource in the collection/page:

"_links": {
    "item": [
        {
            "href": "http://localhost:8080/api/MyResource/1"
        },
        {
            "href": "http://localhost:8080/api/MyResource/2"
        }
    ]
}

However, when there is a single resource in the collection/page, then we don’t get an array:

"_links": {
    "item": {
        "href": "http://localhost:8080/api/MyResource/1"
    }
}

Obviously, this isn’t ideal from the perspective of client that consumes the service. It would be nice if Spring HATEOAS would provide a support for explicitly specifying array serialization for a certain link relations.

[odrotbohm]

A rel is not really tied to a controller nor to a domain type. I guess we can provide a way to configure patterns to match, so that you can simplify the setup to configure this based on the curie used.

[gregturn]

Why don’t you open a new ticket instead of commenting on one that’s been closed and released.