Is there a simple implementation of HATEOAS + Pagination in Spring without data rest?

Question

I've been searching for a few days on how to implement a Spring REST API containing HATEOAS links + Pagination with Spring boot and JPA (No spring data rest) like this random example:

{
    "_links": {
        "first": {
            "href": "http://localhost:8080/api/albums-list?page=0&size=2&sort=title,desc"
        },
        "prev": {
            "href": "http://localhost:8080/api/albums-list?page=0&size=2&sort=title,desc"
        },
        "self": {
            "href": "http://localhost:8080/api/albums-list?page=1&size=2&sort=title,desc"
        },
        "next": {
            "href": "http://localhost:8080/api/albums-list?page=2&size=2&sort=title,desc"
        },
        "last": {
            "href": "http://localhost:8080/api/albums-list?page=4&size=2&sort=title,desc"
        }
    },
    "page": {
        "size": 2,
        "totalElements": 10,
        "totalPages": 5,
        "number": 1
    },
    "_embedded": {
        "albums": [
            {
                "id": 7,
                "title": "Top Hits Vol 7",
                "description": "Top hits vol 7. description",
                "releaseDate": "10-03-1987",
                "actors": [
                    {
                        "id": 4,
                        "firstName": "Janice",
                        "lastName": "Preston",
                        "_links": {
                            "self": {
                                "href": "http://localhost:8080/api/actors/4"
                            }
                        }
                    }
                ],
                "_links": {
                    "self": {
                        "href": "http://localhost:8080/api/actors/7"
                    }
                }
            },
            {
                "id": 6,
                "title": "Top Hits Vol 6",
                "description": "Top hits vol 6. description",
                "releaseDate": "10-03-1986",
                "actors": [
                    {
                        "id": 3,
                        "firstName": "Laverne",
                        "lastName": "Mann",
                        "_links": {
                            "self": {
                                "href": "http://localhost:8080/api/actors/3"
                            }
                        }
                    }
                ],
                "_links": {
                    "self": {
                        "href": "http://localhost:8080/api/actors/6"
                    }
                }
            }
        ]
    }
}

However, the solutions that I've found so far are ridiculously complicated or the amount of boilerplate are laughable This solution for instance: https://howtodoinjava.com/spring5/hateoas/pagination-links/ the tutorial on the page doesn't present it entirely but it requires you to create the entity, a model for the entity, and a long RepresentationModelAssemblerSupport full of boilerplate

I've tried this also: https://spring.io/guides/tutorials/rest/ However the nested classes (i have relations of one to many/many to one) don't get the links for HATEOAS:

{
    "id": 3,
    "nome": "Amazonas",
    "uf": "AM",
    "cidades": [
        {
        //no HATEOAS in here
            "id": 10003,
            "nome": null,
            "instituicoes": [],
            "uf": "AM"
        },
        {
            "id": 219,
            "nome": "Alvarães",
            "instituicoes": [],
            "uf": "AM"
        }
    ],
    "_links": {
        "self": {
            "href": "http://localhost:8080/api/v1/estados/estadoes/3"
        },
        "estadoes": {
            "href": "http://localhost:8080/api/v1/estados/estadoes"
        }
    }
}

I mean, isn't there a simpler solution? Luckily for pagination PagingAndSortingRepository is useful but then having both pagination + HATEOAS, what a nightmare.

Blais

Answer 1

A RepresentationModelAssembler is required. A model class extends EntityModel<T> is unnecessary if you don't need additional fields.

My example entity class is Inventory.

RepresentationModelAssembler. You can add more links here.

@Component
public class InventoryModelAssembler implements RepresentationModelAssembler<Inventory, EntityModel<Inventory>> {

    @Override
    public EntityModel<Inventory> toModel(Inventory inventory) {

        return EntityModel.of(inventory,
                linkTo(methodOn(InventoryController.class).get(inventory.getId()))
                        .withSelfRel());
    }
}

Controller

@RestController
@RequestMapping("/inventories")
@RequiredArgsConstructor
public class InventoryController {

    private final InventoryRepository inventoryRepository;

    private final PagedResourcesAssembler pagedResourcesAssembler;

    private final InventoryModelAssembler inventoryModelAssembler;

    @GetMapping
    public ResponseEntity get(Pageable pageable) {

        Page<Inventory> inventories = inventoryRepository.findAll(pageable);

        return ResponseEntity
                .ok()
                .contentType(MediaTypes.HAL_JSON)
                .body(pagedResourcesAssembler.toModel(inventories, inventoryModelAssembler));
    }
}

HAL JSON response. A full long response can be found in my HTML doc. Download it and open with your browser.

{
  "_embedded" : {
    "inventories" : [ {
      "carrier" : "SG",
      "fltNum" : "001",
      "serviceType" : "PAX",
      "fltDate" : "2020-01-20",
      "fltDow" : 1,
      "createdDate" : "2020-06-11T13:21:44.992Z",
      "lastModifiedDate" : "2020-06-11T13:21:44.992Z",
      "_links" : {
        "self" : {
          "href" : "http://localhost:8080/inventories/5ee22fe8853b0f45ae5fca27"
        }
      }
    }]
  },
  "_links" : {
    "first" : {
      "href" : "http://localhost:8080/inventories?carrier=SG&fltNum=001&page=0&size=10&sort=fltNum,asc&sort=fltDate,desc"
    },
    "self" : {
      "href" : "http://localhost:8080/inventories?carrier=SG&fltNum=001&page=0&size=10&sort=fltNum,asc&sort=fltDate,desc"
    },
    "next" : {
      "href" : "http://localhost:8080/inventories?carrier=SG&fltNum=001&page=1&size=10&sort=fltNum,asc&sort=fltDate,desc"
    },
    "last" : {
      "href" : "http://localhost:8080/inventories?carrier=SG&fltNum=001&page=1&size=10&sort=fltNum,asc&sort=fltDate,desc"
    }
  },
  "page" : {
    "size" : 10,
    "totalElements" : 20,
    "totalPages" : 2,
    "number" : 0
  }
}

Full code is shared in Github. If my project is helpful other than this answer, consider give it a star in Github.

Thermit

I built my assembler using the support class a in public class PostModelAssemblerSupport extends RepresentationModelAssemblerSupport<Post, PostModel> { but it makes the method call pagedResourcesAssembler.toModel(posts, postModelAssemblerSupport); undefined. – Ploch

I followed that guide springcloud.io/post/2022-04/hateoas-spring-boot-and-jpa/… – Ploch

Answer 2

There is an excellent explanation here in this example with code Pagination(with Hateoas), Filtering & Sorting with Spring Boot and JPA Multiple approaches are demonstrated. This covers exactly the appraoch to implement pagination, including sorting and filtering without spring data rest.

Knife

This is a wonderful resource. Clear and to the point. Thanks. – Asclepiadaceous