3. JPA Hateoas 적용하기

2020. 8. 1. 17:13

서론

이번 포스팅에서 왜 Hateoas를 적용해야하는지에 대해서 다루지 않습니다. 이와 관련된 자세한 이응준님의 그런 REST API로 괜찮은가 발표 세션을 꼭 보시기를 권장드리며, 해당 내용을 알고 계시다는 전제하에 포스팅을 작성하겠습니다.

이번에 다룰 내용은 Rest API 작성을 위해 필요한 Hateoas를 기존에 생성한 Page 객체에 적용하는 방법과 PagedResourceAssembler를 Customizing하는 방법을 알아보겠습니다.

1. 기존 Page 객체 이슈

위 그림은 이전 포스팅에서 예제 프로그램 API 호출 결과입니다. 해당 API는 원하는 요청에 대한 결과를 확인할 수 있습니다. 하지만 데이터를 통해서 어떠한 행위들이 가능한지 혹은 메시지가 정확히 어떠한 의미를 포함하고 있는지는 API 결과를 통해 알 수 없습니다.

다시말해 해당 API 결과를 보고서는 customer_id를 통해 어떠한 API를 추가적으로 호출할 수 있는지 어떤 상태 변화가 가능한지 알 수 없습니다.

그렇다면 Hateoas가 적용된 API의 모습은 어떨까요?

[
  {
    "id": 1,
    "node_id": "MDU6SXNzdWUx",
    "url": "https://api.github.com/repos/octocat/Hello-World/issues/1347",
    "repository_url": "https://api.github.com/repos/octocat/Hello-World",
    "labels_url": "https://api.github.com/repos/octocat/Hello-World/issues/1347/labels{/name}",
    "comments_url": "https://api.github.com/repos/octocat/Hello-World/issues/1347/comments",
    "events_url": "https://api.github.com/repos/octocat/Hello-World/issues/1347/events",
    "html_url": "https://github.com/octocat/Hello-World/issues/1347",
    "number": 1347,
    "state": "open",
    "title": "Found a bug",
    "body": "I'm having a problem with this.",
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      "node_id": "MDQ6VXNlcjE=",
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      "gravatar_id": "",
      "url": "https://api.github.com/users/octocat",
      "html_url": "https://github.com/octocat",
      "followers_url": "https://api.github.com/users/octocat/followers",
      "following_url": "https://api.github.com/users/octocat/following{/other_user}",
      "gists_url": "https://api.github.com/users/octocat/gists{/gist_id}",
      "starred_url": "https://api.github.com/users/octocat/starred{/owner}{/repo}",
      "subscriptions_url": "https://api.github.com/users/octocat/subscriptions",
      "organizations_url": "https://api.github.com/users/octocat/orgs",
      "repos_url": "https://api.github.com/users/octocat/repos",
      "events_url": "https://api.github.com/users/octocat/events{/privacy}",
      "received_events_url": "https://api.github.com/users/octocat/received_events",
      "type": "User",
      "site_admin": false
    },
    "labels": [
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        "id": 208045946,
        "node_id": "MDU6TGFiZWwyMDgwNDU5NDY=",
        "url": "https://api.github.com/repos/octocat/Hello-World/labels/bug",
        "name": "bug",
        "description": "Something isn't working",
        "color": "f29513",
        "default": true
      }
    ],
    "assignee": {
      "login": "octocat",
      "id": 1,
      "node_id": "MDQ6VXNlcjE=",
      "avatar_url": "https://github.com/images/error/octocat_happy.gif",
      "gravatar_id": "",
      "url": "https://api.github.com/users/octocat",
      "html_url": "https://github.com/octocat",
      "followers_url": "https://api.github.com/users/octocat/followers",
      "following_url": "https://api.github.com/users/octocat/following{/other_user}",
      "gists_url": "https://api.github.com/users/octocat/gists{/gist_id}",
      "starred_url": "https://api.github.com/users/octocat/starred{/owner}{/repo}",
      "subscriptions_url": "https://api.github.com/users/octocat/subscriptions",
      "organizations_url": "https://api.github.com/users/octocat/orgs",
      "repos_url": "https://api.github.com/users/octocat/repos",
      "events_url": "https://api.github.com/users/octocat/events{/privacy}",
      "received_events_url": "https://api.github.com/users/octocat/received_events",
      "type": "User",
      "site_admin": false
    },
    "assignees": [
      {
        "login": "octocat",
        "id": 1,
        "node_id": "MDQ6VXNlcjE=",
        "avatar_url": "https://github.com/images/error/octocat_happy.gif",
        "gravatar_id": "",
        "url": "https://api.github.com/users/octocat",
        "html_url": "https://github.com/octocat",
        "followers_url": "https://api.github.com/users/octocat/followers",
        "following_url": "https://api.github.com/users/octocat/following{/other_user}",
        "gists_url": "https://api.github.com/users/octocat/gists{/gist_id}",
        "starred_url": "https://api.github.com/users/octocat/starred{/owner}{/repo}",
        "subscriptions_url": "https://api.github.com/users/octocat/subscriptions",
        "organizations_url": "https://api.github.com/users/octocat/orgs",
        "repos_url": "https://api.github.com/users/octocat/repos",
        "events_url": "https://api.github.com/users/octocat/events{/privacy}",
        "received_events_url": "https://api.github.com/users/octocat/received_events",
        "type": "User",
        "site_admin": false
      }
    ],
    "milestone": {
      "url": "https://api.github.com/repos/octocat/Hello-World/milestones/1",
      "html_url": "https://github.com/octocat/Hello-World/milestones/v1.0",
      "labels_url": "https://api.github.com/repos/octocat/Hello-World/milestones/1/labels",
      "id": 1002604,
      "node_id": "MDk6TWlsZXN0b25lMTAwMjYwNA==",
      "number": 1,
      "state": "open",
      "title": "v1.0",
      "description": "Tracking milestone for version 1.0",
      "creator": {
        "login": "octocat",
        "id": 1,
        "node_id": "MDQ6VXNlcjE=",
        "avatar_url": "https://github.com/images/error/octocat_happy.gif",
        "gravatar_id": "",
        "url": "https://api.github.com/users/octocat",
        "html_url": "https://github.com/octocat",
        "followers_url": "https://api.github.com/users/octocat/followers",
        "following_url": "https://api.github.com/users/octocat/following{/other_user}",
        "gists_url": "https://api.github.com/users/octocat/gists{/gist_id}",
        "starred_url": "https://api.github.com/users/octocat/starred{/owner}{/repo}",
        "subscriptions_url": "https://api.github.com/users/octocat/subscriptions",
        "organizations_url": "https://api.github.com/users/octocat/orgs",
        "repos_url": "https://api.github.com/users/octocat/repos",
        "events_url": "https://api.github.com/users/octocat/events{/privacy}",
        "received_events_url": "https://api.github.com/users/octocat/received_events",
        "type": "User",
        "site_admin": false
      },
      "open_issues": 4,
      "closed_issues": 8,
      "created_at": "2011-04-10T20:09:31Z",
      "updated_at": "2014-03-03T18:58:10Z",
      "closed_at": "2013-02-12T13:22:01Z",
      "due_on": "2012-10-09T23:39:01Z"
    },
    "locked": true,
    "active_lock_reason": "too heated",
    "comments": 0,
    "pull_request": {
      "url": "https://api.github.com/repos/octocat/Hello-World/pulls/1347",
      "html_url": "https://github.com/octocat/Hello-World/pull/1347",
      "diff_url": "https://github.com/octocat/Hello-World/pull/1347.diff",
      "patch_url": "https://github.com/octocat/Hello-World/pull/1347.patch"
    },
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    "created_at": "2011-04-22T13:33:48Z",
    "updated_at": "2011-04-22T13:33:48Z",
    "repository": {
      "id": 1296269,
      "node_id": "MDEwOlJlcG9zaXRvcnkxMjk2MjY5",
      "name": "Hello-World",
      "full_name": "octocat/Hello-World",
      "owner": {
        "login": "octocat",
        "id": 1,
        "node_id": "MDQ6VXNlcjE=",
        "avatar_url": "https://github.com/images/error/octocat_happy.gif",
        "gravatar_id": "",
        "url": "https://api.github.com/users/octocat",
        "html_url": "https://github.com/octocat",
        "followers_url": "https://api.github.com/users/octocat/followers",
        "following_url": "https://api.github.com/users/octocat/following{/other_user}",
        "gists_url": "https://api.github.com/users/octocat/gists{/gist_id}",
        "starred_url": "https://api.github.com/users/octocat/starred{/owner}{/repo}",
        "subscriptions_url": "https://api.github.com/users/octocat/subscriptions",
        "organizations_url": "https://api.github.com/users/octocat/orgs",
        "repos_url": "https://api.github.com/users/octocat/repos",
        "events_url": "https://api.github.com/users/octocat/events{/privacy}",
        "received_events_url": "https://api.github.com/users/octocat/received_events",
        "type": "User",
        "site_admin": false
      },
      "private": false,
      "html_url": "https://github.com/octocat/Hello-World",
      "description": "This your first repo!",
      "fork": false,
      "url": "https://api.github.com/repos/octocat/Hello-World",
      "archive_url": "http://api.github.com/repos/octocat/Hello-World/{archive_format}{/ref}",
      "assignees_url": "http://api.github.com/repos/octocat/Hello-World/assignees{/user}",
      "blobs_url": "http://api.github.com/repos/octocat/Hello-World/git/blobs{/sha}",
      "branches_url": "http://api.github.com/repos/octocat/Hello-World/branches{/branch}",
      "collaborators_url": "http://api.github.com/repos/octocat/Hello-World/collaborators{/collaborator}",
      "comments_url": "http://api.github.com/repos/octocat/Hello-World/comments{/number}",
      "commits_url": "http://api.github.com/repos/octocat/Hello-World/commits{/sha}",
      "compare_url": "http://api.github.com/repos/octocat/Hello-World/compare/{base}...{head}",
      "contents_url": "http://api.github.com/repos/octocat/Hello-World/contents/{+path}",
      "contributors_url": "http://api.github.com/repos/octocat/Hello-World/contributors",
      "deployments_url": "http://api.github.com/repos/octocat/Hello-World/deployments",
      "downloads_url": "http://api.github.com/repos/octocat/Hello-World/downloads",
      "events_url": "http://api.github.com/repos/octocat/Hello-World/events",
      "forks_url": "http://api.github.com/repos/octocat/Hello-World/forks",
      "git_commits_url": "http://api.github.com/repos/octocat/Hello-World/git/commits{/sha}",
      "git_refs_url": "http://api.github.com/repos/octocat/Hello-World/git/refs{/sha}",
      "git_tags_url": "http://api.github.com/repos/octocat/Hello-World/git/tags{/sha}",
      "git_url": "git:github.com/octocat/Hello-World.git",
      "issue_comment_url": "http://api.github.com/repos/octocat/Hello-World/issues/comments{/number}",
      "issue_events_url": "http://api.github.com/repos/octocat/Hello-World/issues/events{/number}",
      "issues_url": "http://api.github.com/repos/octocat/Hello-World/issues{/number}",
      "keys_url": "http://api.github.com/repos/octocat/Hello-World/keys{/key_id}",
      "labels_url": "http://api.github.com/repos/octocat/Hello-World/labels{/name}",
      "languages_url": "http://api.github.com/repos/octocat/Hello-World/languages",
      "merges_url": "http://api.github.com/repos/octocat/Hello-World/merges",
      "milestones_url": "http://api.github.com/repos/octocat/Hello-World/milestones{/number}",
      "notifications_url": "http://api.github.com/repos/octocat/Hello-World/notifications{?since,all,participating}",
      "pulls_url": "http://api.github.com/repos/octocat/Hello-World/pulls{/number}",
      "releases_url": "http://api.github.com/repos/octocat/Hello-World/releases{/id}",
      "ssh_url": "git@github.com:octocat/Hello-World.git",
      "stargazers_url": "http://api.github.com/repos/octocat/Hello-World/stargazers",
      "statuses_url": "http://api.github.com/repos/octocat/Hello-World/statuses/{sha}",
      "subscribers_url": "http://api.github.com/repos/octocat/Hello-World/subscribers",
      "subscription_url": "http://api.github.com/repos/octocat/Hello-World/subscription",
      "tags_url": "http://api.github.com/repos/octocat/Hello-World/tags",
      "teams_url": "http://api.github.com/repos/octocat/Hello-World/teams",
      "trees_url": "http://api.github.com/repos/octocat/Hello-World/git/trees{/sha}",
      "clone_url": "https://github.com/octocat/Hello-World.git",
      "mirror_url": "git:git.example.com/octocat/Hello-World",
      "hooks_url": "http://api.github.com/repos/octocat/Hello-World/hooks",
      "svn_url": "https://svn.github.com/octocat/Hello-World",
      "homepage": "https://github.com",
      "language": null,
      "forks_count": 9,
      "stargazers_count": 80,
      "watchers_count": 80,
      "size": 108,
      "default_branch": "master",
      "open_issues_count": 0,
      "is_template": true,
      "topics": [
        "octocat",
        "atom",
        "electron",
        "api"
      ],
      "has_issues": true,
      "has_projects": true,
      "has_wiki": true,
      "has_pages": false,
      "has_downloads": true,
      "archived": false,
      "disabled": false,
      "visibility": "public",
      "pushed_at": "2011-01-26T19:06:43Z",
      "created_at": "2011-01-26T19:01:12Z",
      "updated_at": "2011-01-26T19:14:43Z",
      "permissions": {
        "admin": false,
        "push": false,
        "pull": true
      },
      "allow_rebase_merge": true,
      "template_repository": null,
      "temp_clone_token": "ABTLWHOULUVAXGTRYU7OC2876QJ2O",
      "allow_squash_merge": true,
      "delete_branch_on_merge": true,
      "allow_merge_commit": true,
      "subscribers_count": 42,
      "network_count": 0
    }
  }
]

위 API는 Github의 Issue API 결과입니다. 주요 데이터에 대하여 자신의 URL과 다음 상태 변이에 대한 URL 링크를 같이 제공하여 Hateoas를 준수하고 있습니다. 따라서 Client는 서버로부터 받은 링크를 통해 상태를 변화할 뿐 Client 소스에 하드코딩되어 있을 필요가 없습니다.

Spring에서는 Hateoas 기능을 손쉽게 적용가능하기 위한 Spring Hateoas 프로젝트가 있습니다. 해당 프로젝트를 적용하여, 기존 프로그램 예제를 확장해보도록 하겠습니다.

2. Hateoas 적용

build.gradle

(...중략...)
dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-hateoas'
    (...중략...)
}

위와같이 dependency에 hateoas를 추가합니다.

2-1. Controller

@RestController
@RequiredArgsConstructor
public class CustomerController {
    private final CustomerService service;
    private final PagedResourcesAssembler<CustomerDTO> assembler;

    @GetMapping("/customers")
    public ResponseEntity<PagedModel<EntityModel<CustomerDTO>>> getCustomer(PageableDTO pageableDTO){
        Page<CustomerDTO> customers = service.getCustomer(pageableDTO);
        PagedModel<EntityModel<CustomerDTO>> entityModels = assembler.toModel(customers);
        return ResponseEntity.ok(entityModels);
    }
}

Controller에서 Page 모델을 기본적으로 제공되는 PagedResourcesAssembler를 통해 PagedModel 객체로 변환하는 코드를 추가하였습니다.

2-2. 실행 결과

PagedResourcedAssembler 적용 후 결과를 보면, self 링크를 포함하여 다음 상태 전이를 위한 API가 기본적으로 제공되는 것을 확인할 수 있습니다.

하지만 위 API에서는 각각의 customerDTO 각 원소에 대한 상태 변이 URL은 제공되지 않았습니다. 이를 추가해보겠습니다.

3. PagedModelUtil

public class LinkResource<T> extends EntityModel<T> {
    public static <T> EntityModel<T> of(WebMvcLinkBuilder builder, T model, Function<T,?> resourceFunc){
        return EntityModel.of(model, getSelfLink(builder, model, resourceFunc));
    }

    private static<T> Link getSelfLink(WebMvcLinkBuilder builder, T data, Function<T, ?> resourceFunc){
        WebMvcLinkBuilder slash = builder.slash(resourceFunc.apply(data));
        return slash.withSelfRel();
    }
}

EntityModel을 생성할 때, Link를 주입하도록 LinkResource 클래스를 생성합니다.

public class PagedModelUtil {
    public static <T> PagedModel<EntityModel<T>> getEntityModels(PagedResourcesAssembler<T> assembler,
                                                                 Page<T> page,
                                                                 Class<?> clazz,
                                                                 Function<T, ?> selfLinkFunc ){
        WebMvcLinkBuilder webMvcLinkBuilder = linkTo(clazz);
        return assembler.toModel(page, model -> LinkResource.of(webMvcLinkBuilder, model, selfLinkFunc::apply));
    }

    public static <T> PagedModel<EntityModel<T>> getEntityModels(PagedResourcesAssembler<T> assembler,
                                                                 Page<T> page,
                                                                 WebMvcLinkBuilder builder,
                                                                 Function<T, ?> selfLinkFunc ){
        return assembler.toModel(page, model -> LinkResource.of(builder, model, selfLinkFunc::apply));
    }
}

LinkResource를 기반으로 전체 Page 모델을 순회하면서 Link를 주입하고, 이를 PagedModel 객체로 컨버팅하는 Util 클래스를 생성합니다.

@RestController
@RequiredArgsConstructor
public class CustomerController {
    private final CustomerService service;
    private final PagedResourcesAssembler<CustomerDTO> assembler;

    @GetMapping("/customers")
    public ResponseEntity<PagedModel<EntityModel<CustomerDTO>>> getCustomer(PageableDTO pageableDTO){
        Page<CustomerDTO> customers = service.getCustomer(pageableDTO);

        PagedModel<EntityModel<CustomerDTO>> entityModels = PagedModelUtil.getEntityModels(assembler, customers,
                linkTo(methodOn(this.getClass()).getCustomer(null)),
                CustomerDTO::getCustomerId);
        return ResponseEntity.ok(entityModels);
    }
}

Controller 클래스에서는 해당 Util 클래스 함수 호출을 통해 PagedModel로 변경하도록 코드를 변경헀습니다.

여기서 두번째 및 세번째 인자가 각 DTO별로 호출할 메소드 및 ID 값에 해당합니다.

위 예제에서는 getCustomer 메소드를 두번째 인자로 전달했기 때문에 @GetMapping 어노테이션으로 전달한 customers 가 URL에 추가가 될 것입니다. 또한, customers URL 뒤에올 ID 값으로 customerDTO에 속한 id 값을 넘겨줌으로써 URL이 완성될 것입니다.

따라서, 위 코드를 통해서 각 DTO 별로 추가되는 URL은 http://localhost:8080/customers/{id}가 될 것입니다.

@RestController
@RequiredArgsConstructor
public class CustomerController {
    private final CustomerService service;
    private final PagedResourcesAssembler<CustomerDTO> assembler;

    @GetMapping("/customers")
    public ResponseEntity<PagedModel<EntityModel<CustomerDTO>>> getCustomer(PageableDTO pageableDTO){
        Page<CustomerDTO> customers = service.getCustomer(pageableDTO);

        PagedModel<EntityModel<CustomerDTO>> entityModels = PagedModelUtil.getEntityModels(assembler, customers,
                linkTo(methodOn(this.getClass()).getCustomer(null)),
                v-> v.getCustomerName() + "/" + v.getCustomerId());
        return ResponseEntity.ok(entityModels);
    }
}

만약 URL을 변경하고 싶다면, 위와같이 두번째 인자 및 세번째 Function을 새로 정의하여 변경 가능합니다.

4. PagedResourceAssembler 커스터마이징

지금까지 Hateoas 적용과 각 DTO 별로 Self 링크를 적용하는 방법에 대해서 살펴봤습니다. 기본적으로 제공되는 PagedResourceAssembler에는 첫페이지, 이전 페이지, 현재 페이지, 다음 페이지 및 마지막 페이지 정보가 담겨있습니다.

이는 해당 API가 게시판에 노출되는 API라면 위와 같은 모습에 사용될 수 있는 Link 정보를 담고 있습니다.

만약 사용자가 원하는 게시판의 형태가 위와 같다면, 기본 제공되는 PagedResourcesAssembler는 이를 표현할 수 없습니다. 따라서 Customizing이 필요합니다.

4-1. CustomPagedResourceAssembler

public class CustomPagedResourceAssembler<T> extends PagedResourcesAssembler<T> {
    private final HateoasPageableHandlerMethodArgumentResolver pageableResolver;
    private final Optional<UriComponents> baseUri;
    private final int PAGE_SIZE;
    private final int DEFAULT_PAGE_SIZE = 10;

    public CustomPagedResourceAssembler(HateoasPageableHandlerMethodArgumentResolver pageableResolver, @Nullable  Integer pageSize) {
        super(pageableResolver,null);
        this.pageableResolver = pageableResolver;
        baseUri = Optional.empty();
        this.PAGE_SIZE = pageSize == null ? DEFAULT_PAGE_SIZE : pageSize;
    }

    @Override
    public PagedModel<EntityModel<T>> toModel(Page<T> entity) {
        return toModel(entity, EntityModel::of);
    }

    @Override
    public <R extends RepresentationModel<?>> PagedModel<R> toModel(Page<T> page, RepresentationModelAssembler<T, R> assembler) {
        Assert.notNull(page, "Page must not be null!");
        Assert.notNull(assembler, "ResourceAssembler must not be null!");

        List<R> resources = new ArrayList<>(page.getNumberOfElements());

        for (T element : page) {
            resources.add(assembler.toModel(element));
        }

        PagedModel<R> resource = createPagedModel(resources, asPageMetadata(page), page);
        return addPaginationLinks(resource, page, Optional.empty());
    }

    private PagedModel.PageMetadata asPageMetadata(Page<?> page) {

        Assert.notNull(page, "Page must not be null!");
        int number = page.getNumber();
        return new PagedModel.PageMetadata(page.getSize(), number, page.getTotalElements(), page.getTotalPages());
    }

    private <R> PagedModel<R> addPaginationLinks(PagedModel<R> resources, Page<?> page, Optional<Link> link) {

        UriTemplate base = getUriTemplate(link);
        boolean isNavigable = page.hasPrevious() || page.hasNext();

        int currIndex = page.getNumber();
        int lastIndex = page.getTotalPages() == 0 ? 0 : page.getTotalPages() - 1;
        int baseIndex = (currIndex / this.PAGE_SIZE) * this.PAGE_SIZE;
        int prevIndex = baseIndex - this.PAGE_SIZE;
        int nextIndex = baseIndex + this.PAGE_SIZE;
        int size = page.getSize();
        Sort sort = page.getSort();

        if(lastIndex < currIndex)
            throw new IndexOutOfBoundsException("Page total size must not be less than page size");

        if (isNavigable) {
            resources.add(createLink(base, PageRequest.of(0, size, sort), IanaLinkRelations.FIRST));
        }

        Link selfLink = link.map(it -> it.withSelfRel()).orElseGet(() -> createLink(base, page.getPageable(), IanaLinkRelations.SELF));

        resources.add(selfLink);

        if (prevIndex >= 0) {
            resources.add(createLink(base,
                    PageRequest.of(prevIndex, size, sort),
                    IanaLinkRelations.PREV));
        }

        for(int i = 0; i < this.PAGE_SIZE; i++){
            if(baseIndex + i <= lastIndex){
                resources.add(createLink(base, PageRequest.of(baseIndex + i, size, sort), LinkRelation.of("pagination")));
            }
        }

        if(nextIndex < lastIndex){
            resources.add(createLink(base, PageRequest.of(nextIndex, size, sort), IanaLinkRelations.NEXT));
        }

        if (isNavigable) {
            resources.add(createLink(base, PageRequest.of(lastIndex, size, sort), IanaLinkRelations.LAST));
        }

        return resources;
    }

    private UriTemplate getUriTemplate(Optional<Link> baseLink) {
        return UriTemplate.of(baseLink.map(Link::getHref).orElseGet(this::baseUriOrCurrentRequest));
    }

    private String baseUriOrCurrentRequest() {
        return baseUri.map(Object::toString).orElseGet(CustomPagedResourceAssembler::currentRequest);
    }

    private static String currentRequest() {
        return ServletUriComponentsBuilder.fromCurrentRequest().build().toString();
    }

    private Link createLink(UriTemplate base, Pageable pageable, LinkRelation relation) {
        UriComponentsBuilder builder = fromUri(base.expand());
        pageableResolver.enhance(builder, getMethodParameter(), pageable);
        return Link.of(UriTemplate.of(builder.build().toString()), relation);
    }
}

위 코드는 기존 PagedResourcesAssembler를 상속받아 구현하였습니다. 가장 핵심이 되는 부분은 addPaginationLinks 메소드이며, 해당 메소드를 통해 페이지의 인덱스 정보를 pagination 링크아래에 배치하도록 표현했습니다.

@Configuration
public class AppConfig implements WebMvcConfigurer {

    ...(중략)...

    @Bean
    public CustomPagedResourceAssembler<?> customPagedResourceAssembler(){
        return new CustomPagedResourceAssembler<>(new HateoasPageableHandlerMethodArgumentResolver(),10);
    }
}

이후 해당 클래스를 Bean으로 등록시켜 줍니다. 생성자의 두번째 파라미터는 Page 사이즈를 결정하며, 해당 값의 변경을 통해 노출되는 URL 크기가 달라집니다.

4-2 Controller

@RestController
@RequiredArgsConstructor
public class CustomerController {
    private final CustomerService service;
    private final CustomPagedResourceAssembler<CustomerDTO> assembler;

    @GetMapping("/customers")
    public ResponseEntity<PagedModel<EntityModel<CustomerDTO>>> getCustomer(PageableDTO pageableDTO){
        Page<CustomerDTO> customers = service.getCustomer(pageableDTO);

        PagedModel<EntityModel<CustomerDTO>> entityModels = PagedModelUtil.getEntityModels(assembler, customers,
                linkTo(methodOn(this.getClass()).getCustomer(null)),
                CustomerDTO::getCustomerId);
        return ResponseEntity.ok(entityModels);
    }
}

Bean으로 등록한 CustomPagedResourceAssembler로 주입받도록 코드를 수정했습니다.

4-3 결과

애플리케이션 구동 후 해당 URL을 호출하면, 정상적으로 페이지 URL이 표시되는 것을 확인할 수 있습니다.

마치며

Page 객체에 Hateoas를 적용하는 방법에 대해서 살펴봤습니다. Rest API 설계를 위해서는 Hateoas 적용뿐만 아니라 Self-descriptive-messages를 적용하기 위해 IANA 등록 혹은 Profile 링크를 추가해야합니다.

Profile 링크를 적용하기 위해서 RestDocs 혹은 Swagger 등을 활용할 수 있으니 참고 바랍니다.

저작자표시 비영리 변경금지

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