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🎛 Rest controller with Spring HATEOAS
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‎hello-spring-hateoas/src/main/java/kr/ac/hansung/cse/hellospringhateoas/assembler/ActorModelAssembler.java

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package kr.ac.hansung.cse.hellospringhateoas.assembler;
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import kr.ac.hansung.cse.hellospringhateoas.controller.WebController;
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import kr.ac.hansung.cse.hellospringhateoas.entity.ActorEntity;
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import kr.ac.hansung.cse.hellospringhateoas.entity.AlbumEntity;
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import kr.ac.hansung.cse.hellospringhateoas.model.ActorModel;
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import kr.ac.hansung.cse.hellospringhateoas.model.AlbumModel;
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import org.springframework.hateoas.CollectionModel;
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import org.springframework.hateoas.server.mvc.RepresentationModelAssemblerSupport;
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import org.springframework.stereotype.Component;
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import java.util.Collections;
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import java.util.List;
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import java.util.stream.Collectors;
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import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.linkTo;
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import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.methodOn;
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@Component
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public class ActorModelAssembler
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extends RepresentationModelAssemblerSupport<ActorEntity, ActorModel> {
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public ActorModelAssembler() {
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super(WebController.class, ActorModel.class);
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}
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@Override
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public ActorModel toModel(ActorEntity entity)
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{
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ActorModel actorModel = instantiateModel(entity);
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actorModel.add(linkTo(methodOn(WebController.class).getActorById(entity.getId()))
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.withSelfRel() );
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actorModel.setId(entity.getId());
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actorModel.setFirstName(entity.getFirstName());
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actorModel.setLastName(entity.getLastName());
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actorModel.setBirthDate(entity.getBirthDate());
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actorModel.setAlbums(toAlbumModel(entity.getAlbums()));
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return actorModel;
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}
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@Override
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public CollectionModel<ActorModel> toCollectionModel(Iterable<? extends ActorEntity> entities)
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{
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CollectionModel<ActorModel> actorModels = super.toCollectionModel(entities);
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actorModels.add(linkTo(methodOn(WebController.class).getAllActors()).withSelfRel());
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return actorModels;
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}
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private List<AlbumModel> toAlbumModel(List<AlbumEntity> albums) {
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if (albums.isEmpty())
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return Collections.emptyList();
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return albums.stream()
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.map(album -> AlbumModel.builder()
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.id(album.getId())
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.title(album.getTitle())
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.build()
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.add(linkTo(methodOn(WebController.class).getAlbumById(album.getId()))
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.withSelfRel()))
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.collect(Collectors.toList());
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}
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}

‎hello-spring-hateoas/src/main/java/kr/ac/hansung/cse/hellospringhateoas/assembler/AlbumModelAssembler.java

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package kr.ac.hansung.cse.hellospringhateoas.assembler;
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import kr.ac.hansung.cse.hellospringhateoas.controller.WebController;
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import kr.ac.hansung.cse.hellospringhateoas.entity.ActorEntity;
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import kr.ac.hansung.cse.hellospringhateoas.entity.AlbumEntity;
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import kr.ac.hansung.cse.hellospringhateoas.model.ActorModel;
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import kr.ac.hansung.cse.hellospringhateoas.model.AlbumModel;
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import org.springframework.hateoas.CollectionModel;
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import org.springframework.hateoas.server.mvc.RepresentationModelAssemblerSupport;
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import org.springframework.stereotype.Component;
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import java.util.Collections;
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import java.util.List;
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import java.util.stream.Collectors;
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import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.linkTo;
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import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.methodOn;
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// Class RepresentationModelAssemblerSupport<T,D extends RepresentationModel<D>>
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@Component
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public class AlbumModelAssembler
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extends RepresentationModelAssemblerSupport<AlbumEntity, AlbumModel> {
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// Creates a new RepresentationModelAssemblerSupport
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// using the given controller class and resource type.
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public AlbumModelAssembler() {
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super(WebController.class, AlbumModel.class);
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}
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// D toModel(T entity); Converts the given entity into a D, which extends RepresentationModel.
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@Override
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public AlbumModel toModel(AlbumEntity entity)
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{
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// Instantiates the resource object
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AlbumModel albumModel = instantiateModel(entity);
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albumModel.add(linkTo(methodOn(WebController.class).getAlbumById(entity.getId()) )
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.withSelfRel() );
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albumModel.setId(entity.getId());
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albumModel.setTitle(entity.getTitle());
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albumModel.setDescription(entity.getDescription());
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albumModel.setReleaseDate(entity.getReleaseDate());
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albumModel.setActors(toActorModel(entity.getActors()));
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return albumModel;
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}
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// CollectionModel<D> toCollectionModel(Iterable<? extends T> entities)
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// Converts an Iterable or Ts into an Iterable of RepresentationModel and
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// wraps them in a CollectionModel instance.
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@Override
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public CollectionModel<AlbumModel> toCollectionModel(Iterable<? extends AlbumEntity> entities)
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{
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CollectionModel<AlbumModel> actorModels = super.toCollectionModel(entities);
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actorModels.add(linkTo(methodOn(WebController.class).getAllAlbums()).withSelfRel());
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return actorModels;
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}
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private List<ActorModel> toActorModel(List<ActorEntity> actors) {
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if (actors.isEmpty())
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return Collections.emptyList();
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return actors.stream()
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.map(actor -> ActorModel.builder()
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.id(actor.getId())
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.firstName(actor.getFirstName())
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.lastName(actor.getLastName())
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.build()
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.add(linkTo(
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methodOn(WebController.class)
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.getActorById(actor.getId()))
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.withSelfRel()))
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.collect(Collectors.toList());
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}
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}

‎hello-spring-hateoas/src/main/java/kr/ac/hansung/cse/hellospringhateoas/controller/WebController.java

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package kr.ac.hansung.cse.hellospringhateoas.controller;
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import kr.ac.hansung.cse.hellospringhateoas.assembler.ActorModelAssembler;
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import kr.ac.hansung.cse.hellospringhateoas.assembler.AlbumModelAssembler;
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import kr.ac.hansung.cse.hellospringhateoas.entity.ActorEntity;
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import kr.ac.hansung.cse.hellospringhateoas.entity.AlbumEntity;
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import kr.ac.hansung.cse.hellospringhateoas.model.ActorModel;
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import kr.ac.hansung.cse.hellospringhateoas.model.AlbumModel;
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import kr.ac.hansung.cse.hellospringhateoas.repository.ActorRepository;
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import kr.ac.hansung.cse.hellospringhateoas.repository.AlbumRepository;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.hateoas.CollectionModel;
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import org.springframework.http.HttpStatus;
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import org.springframework.http.ResponseEntity;
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import org.springframework.web.bind.annotation.GetMapping;
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import org.springframework.web.bind.annotation.PathVariable;
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import org.springframework.web.bind.annotation.RestController;
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import java.util.List;
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@RestController
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public class WebController {
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@Autowired
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private AlbumRepository albumRepository;
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@Autowired
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private ActorRepository actorRepository;
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@Autowired
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private ActorModelAssembler actorModelAssembler;
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@Autowired
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private AlbumModelAssembler albumModelAssembler;
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@GetMapping("/api/actors")
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public ResponseEntity<CollectionModel<ActorModel>> getAllActors()
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{
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List<ActorEntity> actorEntities = (List<ActorEntity>) actorRepository.findAll();
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return ResponseEntity.ok(actorModelAssembler.toCollectionModel(actorEntities));
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}
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// Optional
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//The map call is simply used to transform a value to some other value.
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// The orElse() method is used to retrieve the value wrapped inside an Optional instance.
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// It takes one parameter, which acts as a default value.
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// The orElse() method returns the wrapped value if it's present, and its argument otherwise:
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@GetMapping("/api/actors/{id}")
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public ResponseEntity<ActorModel> getActorById(@PathVariable("id") Long id)
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{
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return actorRepository.findById(id)
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.map(actorModelAssembler::toModel)
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.map(ResponseEntity::ok)
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.orElse(ResponseEntity.notFound().build());
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}
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@GetMapping("/api/albums")
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public ResponseEntity<CollectionModel<AlbumModel>> getAllAlbums()
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{
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List<AlbumEntity> albumEntities = (List<AlbumEntity>) albumRepository.findAll();
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return new ResponseEntity<>(
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albumModelAssembler.toCollectionModel(albumEntities),
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HttpStatus.OK);
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}
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@GetMapping("/api/albums/{id}")
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public ResponseEntity<AlbumModel> getAlbumById(@PathVariable("id") Long id)
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{
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return albumRepository.findById(id)
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.map(albumModelAssembler::toModel)
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.map(ResponseEntity::ok)
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.orElse(ResponseEntity.notFound().build());
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}
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}

‎hello-spring-hateoas/src/main/java/kr/ac/hansung/cse/hellospringhateoas/model/ActorModel.java

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package kr.ac.hansung.cse.hellospringhateoas.model;
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// These are DTO objects which will be returned from controller classes as representation models.
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import com.fasterxml.jackson.annotation.JsonInclude;
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import lombok.*;
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import org.springframework.hateoas.RepresentationModel;
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import org.springframework.hateoas.server.core.Relation;
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import java.util.List;
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@Getter
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@Setter
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@Builder
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@NoArgsConstructor
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@AllArgsConstructor
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@EqualsAndHashCode(callSuper = false)
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@Relation(collectionRelation = "actors", itemRelation = "actor")
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@JsonInclude(JsonInclude.Include.NON_NULL)
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public class ActorModel extends RepresentationModel<ActorModel>
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{
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private Long id;
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private String firstName;
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private String lastName;
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private String birthDate;
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private List<AlbumModel> albums;
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}

‎hello-spring-hateoas/src/main/java/kr/ac/hansung/cse/hellospringhateoas/model/AlbumModel.java

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package kr.ac.hansung.cse.hellospringhateoas.model;
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import com.fasterxml.jackson.annotation.JsonInclude;
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import lombok.*;
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import org.springframework.hateoas.RepresentationModel;
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import org.springframework.hateoas.server.core.Relation;
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import java.util.List;
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// These are DTO objects which will be returned from controller classes as representation models.
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@Getter
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@Setter
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@Builder
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@NoArgsConstructor
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@AllArgsConstructor
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@EqualsAndHashCode(callSuper = false)
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@Relation(collectionRelation = "albums", itemRelation = "album")
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@JsonInclude(JsonInclude.Include.NON_NULL)
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public class AlbumModel extends RepresentationModel<AlbumModel>
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{
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private Long id;
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private String title;
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private String description;
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private String releaseDate;
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private List<ActorModel> actors;
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}

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