java - 直接自引用导致循环父类(super class)问题 JSON

Question

我尝试了一些在搜索时发现的方法，但没有任何帮助，或者我没有正确实现。

我得到的错误

Direct self-reference leading to cycle (through reference chain: io.test.entity.bone.Special["appInstance"]->io.test.entity.platform.ApplicationInstance["appInstance"])

它们都扩展了基础实体，并且在基础(父类(super class))中它也有一个 appInstance。

基本实体看起来与此类似

@MappedSuperclass
public abstract class BaseEntity implements Comparable, Serializable {

@ManyToOne
protected ApplicationInstance appInstance;

//getter & setter

}

应用实体看起来像这样

public class ApplicationInstance extends BaseEntity implements Serializable { 
   private List<User> users;
// some other properties (would all have the same base and application instance . User entity will look similar to the Special.)
}

特殊实体

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "objectType")
@JsonIgnoreProperties({"createdBy", "appInstance", "lastUpdatedBy"})
public class Special extends BaseEntity implements Serializable {

    @NotNull
    @Column(nullable = false)
    private String name;

    @Column(length = Short.MAX_VALUE)
    private String description;

    @NotNull
    @Column(nullable = false)
    private Double price;

    @OneToOne
    private Attachment image;

    @Enumerated(EnumType.STRING)
    @ElementCollection(targetClass = SpecialTag.class)
    @CollectionTable(name = "special_tags")
    @Column(name = "specialtag")
    private List<SpecialTag> specialTags;

    @Temporal(TemporalType.TIME)
    private Date specialStartTime;

    @Temporal(TemporalType.TIME)
    private Date specialEndTime;

    @Enumerated(EnumType.STRING)
    @ElementCollection(targetClass = WeekDay.class)
    @CollectionTable(name = "available_week_days")
    @Column(name = "weekday")
    private List<WeekDay> availableWeekDays;

    @OneToMany(mappedBy = "special", cascade = CascadeType.REFRESH)
    private List<SpecialStatus> statuses;

    @OneToMany(mappedBy = "special", cascade = CascadeType.REFRESH)
    private List<SpecialReview> specialReviews;

    @Transient
    private Integer viewed;

    private Boolean launched;

    @OneToMany(mappedBy = "special")
    private List<CampaignSpecial> specialCampaigns;


  @Override
  @JsonIgnore
  public ApplicationInstance getAppInstance() {
    return super.getAppInstance(); 
  }
}

Special 中的所有实体都继承自包含 AppInstance 的 BaseEntity

那我有办法得到特殊的

@GET
@Path("{ref}")
@Produces(MediaType.APPLICATION_JSON)
@Consumes(value = MediaType.TEXT_PLAIN)
public Special findByGuestRef(@PathParam("ref") String pRefeference) {
  // find the special and return it
 return special;
}

在特殊实体上我尝试了以下操作

• 添加了 jsonIgnoreProperties
• 为 appInstance 添加了一个覆盖以使用 @JsonIgnore 进行注释
• @JsonIdentityInfo

上面的链接

• https://stackoverflow.com/a/29632358/4712391
• Jackson serialization: how to ignore superclass properties
• jackson self reference leading to cycle

这些解决方案都不起作用。我做错了什么吗？

注意:是否也可以只编辑特殊的，因为其他实体在不同的包中并且不想编辑它们。

Answer 1

通常在响应中排除属性就像在它们的 getter 中添加一个 @JsonIgnore 注解一样简单，但是如果你不想在父类中添加这个注解，你可以覆盖 getter然后在上面添加注解:

public class Special extends BaseEntity implements Serializable {
    ...
    @JsonIgnore
    public ApplicationInstance getAppInstance() {
        return this.appInstance;
    }
    ...
}

注意:由于有多个框架，请确保您使用的是正确的 @JsonIgnore 注释，否则它将被忽略，请参阅 this answer例如。

另一个选项，更“手动”，只是为响应创建一个 bean，它将是特殊实例的一个子集:

@GET
@Path("{ref}")
@Produces(MediaType.APPLICATION_JSON)
@Consumes(value = MediaType.TEXT_PLAIN)
public SpecialDTO findByGuestRef(@PathParam("ref") String pRefeference) {
  // find the special and return it
 return new SpecialDTO(special);
}


public class SpecialDTO {

    //declare here only the attributes that you want in your response

    public SpecialDTO(Special sp) {
        this.attr=sp.attr; // populate the needed attributes
    }

}