JAX-RS Collection Filter

Just a small helper for making collections in your RESTful APIs even more beautiful:

• When returning collections, add a header stating the number of elements. Clients can then for example HEAD the resource and simply get a count.
• Automatic pagination of your collections

To get started, get the latest version from jitpack:

https://jitpack.io/#larscheid-schmitzhermes/collection-size-filter/

Result Count (Collection Size)

For the result count simply annotate your service method with @CollectionSize.

@Path("/entities")
@CollectionSize
public Response getMyEntities(){
    Collection<String> entities = Arrays.asList("A", "B", "C");
    return Response.ok(entities).build();
}

The answer will look like this:

HTTP/1.1 200
result-count: 3
Content-Type: application/json
[
  "A", "B", "C"
]

The result-count header is automatically added to your Response. You can customize the header name by specifiying it in the annotation like so: @Collection(headerName="my-fancy-header-name")

Fully Automatic Pagination

For automatic pagination, annotate your service method with @Paginated.

@Path("/entities")
@Paginated
@CollectionSize
public Response getMyEntities(){
    Collection<String> entities = Arrays.asList("A", "B", "C", "D", "E");
    return Response.ok(entities).build();
}

Suppose a request like this:

GET /entities HTTP/1.1
offset: 1
limit: 2

or alternatively like this:

GET /entities?offset=1&limit=2 HTTP/1.1

(Even a mix will work, query params always take precedence)

The answer will look like this:

HTTP/1.1 200
total-result-count: 5
offset: 1
limit: 2
result-count: 2
Content-Type: application/json
[
  "B", "C"
]

Notice that I annotated @CollectionSize once again to get my resulting collection's size into the headers! This will usually be the same as limit, only for the last piece of a collection it might be smaller.

Hints

• The functionality is generally applied for every status code and request type. When the returned entity is no collection, @CollectionSize will set result-count: 1. @Paginated ignores non-collection type entities.
• If you don't use class path scanning (hint: you shouldn't), you need to list de.larscheidschmitzhermes.collections.CollectionFilter and/or de.larscheidschmitzhermes.collections.PaginationFilter in your javax.ws.rs.core.Application. (Or whereever else you register your resource classes)

License

MIT