JSON 和 Hibernate JPA 的无限递归

Question

使用spring Boot，尝试将JPA对象转换为JSON时，我不断收到此错误：

nested exception is 
  `org.springframework.http.converter.HttpMessageNotWritableException:
     Could not write JSON: Infinite recursion (StackOverflowError); 
    nested exception is com.fasterxml.jackson.databind.
JsonMappingException: Infinite recursion (StackOverflowError)
 (through reference chain: interv.Entities.AppUser["projects"]->org.hibernate.collection.internal.PersistentBag[0]->interv.Entities.Project["appUser"]->interv.Entities.AppUser["projects"]->org.hibernate.collection.internal.Persis`

按照堆栈溢出的一些解决方案，我通过添加注释来结束 @JsonIgnoreProperties，所以我的实体项目看起来像这样：

@Entity
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Project implements Serializable{

        @Id @GeneratedValue
        private long id;
        private String intitule;
        private String description;

        @OneToMany(mappedBy = "project" , fetch = FetchType.EAGER)
       @Fetch(value = FetchMode.SUBSELECT)
        @JsonIgnoreProperties("contrats")
        private Collection<Contrat> contrats;

        @ManyToOne
        @JoinColumn(name = "Id_appUser")
        @JsonIgnoreProperties("appUser")
        private AppUser appUser;
 }

restful 的 API 是这样的：

    import java.util.List;

@RestController
public class ProjectsController {

    @Autowired
    private ProjectRepo projectRepo;

    @RequestMapping(path = "/ListProjects", method = RequestMethod.GET)
    public List<Project> getProjects(){
        return projectRepo.findAll();
    }

我尝试了其他注释，但我一直收到同样的错误：

在 ARC 扩展中我得到：

200 正常

解析 JSON 数据时出错

JSON 输入意外结束

提前感谢您的帮助:)。

编辑：

文件 AppUser.java

@Entity
@Data
@AllArgsConstructor @NoArgsConstructor
public class AppUser implements Serializable {

    @Id @GeneratedValue
    private Long id;
    @Column(unique = true)
    private String username;
    private String password;
    @ManyToMany(fetch = FetchType.EAGER)
    private Collection<AppRole> roles = new ArrayList<>();

    @OneToMany(mappedBy = "appUser" , fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    private Collection<Project> projects = new ArrayList<>();


    @OneToMany(mappedBy = "appUser" , fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    private Collection<Intervention> interventions = new ArrayList<>();

    @OneToMany(mappedBy = "appUser" , fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    private Collection<Contrat> contrats = new ArrayList<>();

}

Answer 1

出现问题是因为生成 JSON 时存在无限循环。您可以使用@JsonManagedReference 和@JsonBackReference 来解决无限递归。

@Entity
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Project implements Serializable{

        @Id @GeneratedValue
        private long id;
        private String intitule;
        private String description;

        @OneToMany(mappedBy = "project" , fetch = FetchType.EAGER)
       @Fetch(value = FetchMode.SUBSELECT)
        @JsonIgnoreProperties("contrats")
        private Collection<Contrat> contrats;

        @ManyToOne
        @JoinColumn(name = "Id_appUser")
        @JsonBackReference
        private AppUser appUser;
 }

应用用户

@Entity
@Data
@AllArgsConstructor @NoArgsConstructor
public class AppUser implements Serializable {

    @Id @GeneratedValue
    private Long id;
    @Column(unique = true)
    private String username;
    private String password;
    @ManyToMany(fetch = FetchType.EAGER)
    private Collection<AppRole> roles = new ArrayList<>();

    @OneToMany(mappedBy = "appUser" , fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    @JsonManagedReference
    private Collection<Project> projects = new ArrayList<>();


    @OneToMany(mappedBy = "appUser" , fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    private Collection<Intervention> interventions = new ArrayList<>();

    @OneToMany(mappedBy = "appUser" , fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    private Collection<Contrat> contrats = new ArrayList<>();

}