What's the best way to add a new Object using the HTTP POST call through Spring?

I'm learning the Spring Framework and I'm struggling with the Rest services with spring, in particular for the POST call that it's supposed to add a new object to the database.
I've seen a lot of different implementations through the web, but I don't know how to pick the best.

Let's take for example a film class:

@Entity
public class Film {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private long id;

  private String title;

  private String description;

  //Constructor, Getter and Setter Omitted.
}

Assuming the repository extends the JpaRepository<Film,Long>, this would be the Controller class:

@RestController
public class FilmController {

  @Autowired
  FilmRepository filmRepository;
 
  //Implementation #1
  @PostMapping("/film")
  public Film addNew(@RequestBody Map<String,String> body){
    String title = body.get("title");
    String description = body.get("description");
    return filmRepository.save(new Film(title,description));
  }
  
  //Implementation #2
  @PostMapping("/film")
  public Film addNew(String title, String description){
    Film film = new Film(title,description);
    System.out.println(film.getTitle() + " " + film.getDescription());
    return filmRepository.save(film);
  }

  //Implementation #3
  @PostMapping("/film")
  public Film addNew(@RequestBody Film newFilm){
    return filmRepository.save(newFilm);
  }

}

Why some implementations have as parameter a Map<String, String> ? Is that a body mapped to a key/value pair ?

Also bear in mind that I managed to implement correctly just the implementation #2, the first and the third gave me a

415 error:"Unsupported Media Type" org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'multipart/form-data;boundary=--------------------------901298977805450214809889;charset=UTF-8' not supported]

(Despite I followed the official Spring tutorial) on REST services.

I also read something about the creation of DTO classes where I can define attributes without exposing the object to the controller, how can be implemented such solution?

• Why some implementations have as parameter a Map<String, String> ?<br/>
  some implementations use map<key,value> because they need the properties that map interface provide such as non-duplicate key value or the classes that implement map interface such as TreeMap and LinkedHashMap.
• about your implementation of the class FilmController i think its not necessary to use map<String,String> for posting your domain in the data base simply you can have this implementation

@RestController
public class FilmController {

  @Autowired
  FilmRepository filmRepository;
 
  @PostMapping("/film")
  public ResponseEntity addNew(@RequestBody Film film){
return ResponseEntity.ok(filmRepository.save(film));

Implementation 3 is the best practice, but you should create a lightweight DTO class (maybe FilmDto) to avoid exposing the internal structure of your entity, please see LocalDTO, Martin Fowler.

You may use ModelMapper to map FilmDto to Film, and make sure there are proper getters and setters in both classes, if the getters and setters have the same names in both classes, then ModelMapper will do the conversion smoothly:

public class FilmDto {
    private long id;
    private String title;
    private String description;

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}

and you controller:

@RestController
@RequestMapping("/api")
public class FilmController {

    private final FilmRepository filmRepository;
    private ModelMapper modelMapper = new ModelMapper();
    @Autowired
    public FilmController(FilmRepository filmRepository) {
        this.filmRepository = filmRepository;
    }


    //Implementation #3
    @PostMapping("/film")
    public ResponseEntity<FilmDto> addNew(@RequestBody FilmDto  filmDto){
        Film newFilm = modelMapper.map(filmDto, Film.class);
        newFilm = filmRepository.save(newFilm);
        filmDto.setId(newFilm.getId());//you may use modelMapper here

        return ResponseEntity.ok(filmDto);
    }
}

you can test using postman by passing the film as below:

{
    "title": "some title",
    "description": "some description"
}

and the body should be of type "raw", "JSON".