在 java/spring-boot 中，如果找不到項目，返回空 json 對象的最干凈的方法是什么

Question

下面是我用於/api/speaker/123請求處理程序的Java/spring-boot控制器代碼：

@GetMapping
@RequestMapping("{id}")
public Speaker get(@PathVariable Long id) {
    return speakerRepository.getOne(id);
}

如果未找到傳入請求/api/speaker/123的id 123 ，那么如何快速編碼以將空對象/json 返回給瀏覽器？ 在 Nodejs/JavaScript 世界中，我可以簡單地在一行以下做。 任何這樣干凈的代碼而不必添加if...else then，更多代碼來查找null/empty ，然后做更多...然后返回！

return speakerRepository.getOne(id) || {};

編輯：

// Speaker.java
@Entity(name = "speakers")
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class Speaker {
    public Long getSpeaker_id() {
        return speaker_id;
    }

    public void setSpeaker_id(Long speaker_id) {
        this.speaker_id = speaker_id;
    }

    public String getFirst_name() {
        return first_name;
    }

    public void setFirst_name(String first_name) {
        this.first_name = first_name;
    }

    public String getLast_name() {
        return last_name;
    }

    public void setLast_name(String last_name) {
        this.last_name = last_name;
    }

    public String getTitle() {
        return title;
    }

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

    public String getCompany() {
        return company;
    }

    public void setCompany(String company) {
        this.company = company;
    }

    public String getSpeaker_bio() {
        return speaker_bio;
    }

    public void setSpeaker_bio(String speaker_bio) {
        this.speaker_bio = speaker_bio;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long speaker_id;
    private String first_name;
    private String last_name;
    private String title;
    private String company;
    private String speaker_bio;

    public List<Session> getSessions() {
        return sessions;
    }

    @ManyToMany(mappedBy = "speakers")
    @JsonIgnore
    private List<Session> sessions;
    public Speaker(){

    }
}




// SpeakerRepository.java
public interface SpeakerRepository extends JpaRepository<Speaker, Long> {       
}

Answer 1

@GetMapping
@RequestMapping("{id}")
public Speaker get(@PathVariable Long id) {
    return speakerRepository.getOne(id);
}

而是使用以下代碼：

@JsonSerialize
public class EmptyJsonResponse {}



@GetMapping
@RequestMapping("{id}")
public ResponseEntity<?> get(@PathVariable Long id) {
   Speaker speaker = speakerRepository.getOne(id);
    if(speaker != null){
      return new ResponseEntity<Speaker>(speaker, HttpStatus.OK)
    }else{
      return new ResponseEntity<EmptyJsonResponse>(new EmptyJsonResponse(), HttpStatus.OK)
   }         
}