Hibernate-JPA中的无限递归

Question

在错误下面，我得到了无限递归。

Resolved [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: org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSDocumentClass$HibernateProxy$u3IXr3xN["groups"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSGroupBean["docClasses"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSDocumentClass$HibernateProxy$u3IXr3xN["groups"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSGroupBean["docClasses"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSDocumentClass$HibernateProxy$u3IXr3xN["groups"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSGroupBean["docClasses"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSDocumentClass$HibernateProxy$u3IXr3xN["groups"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSGroupBean["docClasses"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSDocumentClass$HibernateProxy$u3IXr3xN["groups"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSGroupBean["docClasses"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSDocumentClass$HibernateProxy$u3IXr3xN["groups"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSGroupBean["docClasses"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSDocumentClass$HibernateProxy$u3IXr3xN["groups"]->org.hibernate.collection.internal.PersistentBag[0]->com.dms.bean.DMSGroupBean["docClasses"]]

下面是我的代码

    @Entity
    @Table(name="DMS_Document_Class")
    public class DMSDocumentClass {

        @Id
        @GeneratedValue(strategy=GenerationType.AUTO)
        @Column(name="DocumentClass_Index_ID")
        private long docClassindexID;


        @ManyToMany(fetch = FetchType.LAZY)
        @JoinTable(name = "DOCCLASS_GROUP", 
        joinColumns = {@JoinColumn(referencedColumnName ="DocumentClass_Index_ID")}, inverseJoinColumns = {@JoinColumn(referencedColumnName="groupID")})
        private List<DMSGroupBean> groups;


        @Column(name="Document_Class_Name")
        private String documentClassName;

        @Column(name="Document_Priority")
        private int documentPriority;

        @Column(name="createdDate")
        private Date createdDate;

        @Column(name="createdBy")
        private String createdBy;

另一个类

    @Entity
    @Table(name="DMS_Group", indexes= @Index(columnList="groupName"),
                uniqueConstraints={@UniqueConstraint(columnNames={"groupName"})})
    public class DMSGroupBean {

        @Id
        @GeneratedValue(strategy=GenerationType.AUTO)
        @Column(name="groupID")
        private long groupID;

        @Column(name="groupName")
        private String groupName;

        @Column(name="createDate")
        private Date createDate;

        @ManyToMany(mappedBy = "groups",fetch = FetchType.LAZY)
        private List<DMSUser> users;

        @ManyToMany(mappedBy = "groups",fetch = FetchType.LAZY)
        private List<DMSDocumentClass> docClasses;

        @Transient
        private String status;

我无法理解为什么在UI上获取此值时会出现此错误。

    @Transactional
        public HashMap<String, Object> getDocListByFolderID(@NonNull long folderID, HttpSession session) {



            DMSFolder currentFolder = folderRepo.findById(folderID).get();

            List<DMSDocument> documents =  documentRepository.findByDocumentFolderID(folderID);

            List<DMSFolder> fetchedSubfolders = folderRepo.findByParentFolderID(folderID);

            //Allow those folder which has rights for this user
            DMSUser userInfo = (DMSUser) session.getAttribute("userinfo");
            List<DMSGroupBean> groups = userInfo.getGroups();//userInfo.getGroupRights();

            List<DMSFolder> finalSubfolders = fetchFinalSubFolders(groups, fetchedSubfolders);

            DMSFolder parentFolder = null;
            if(currentFolder.getParentFolderID() != 0) {
                parentFolder = folderRepo.findById(currentFolder.getParentFolderID()).get();
            }


            HashMap<String, Object> docList = new HashMap<String, Object>();

            docList.put("currentFolder", currentFolder);
            docList.put("documents", documents);
            docList.put("subfolders", finalSubfolders);
            docList.put("parentFolder", parentFolder);

            return docList;
        }

Answer 1

当您拥有StackOverflowException实体的双向关系时，您将获得此JPA。当Jackson试图反序列化它时，它会跟随你的对象图，这个对象图永远不会结束，因为DMSGroupBean和DMSDocumentClass正在引用它自己。

考虑在关系的一个站点上使用@JsonIgnore，如下所示：

@Entity
@Table(name="DMS_Group", indexes= @Index(columnList="groupName"),
            uniqueConstraints={@UniqueConstraint(columnNames={"groupName"})})
public class DMSGroupBean {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="groupID")
    private long groupID;

    @Column(name="groupName")
    private String groupName;

    @Column(name="createDate")
    private Date createDate;

    @ManyToMany(mappedBy = "groups",fetch = FetchType.LAZY)
    private List<DMSUser> users;

    @ManyToMany(mappedBy = "groups",fetch = FetchType.LAZY)
    @JsonIgnore // here
    private List<DMSDocumentClass> docClasses;

    @Transient
    private String status;

}

Answer 2

如前所述，是双向映射导致了这个问题。JsonIgnore将解决您的问题，但是，我建议您使用JsonManagedReference和JsonBackReference。不同之处在于JsonIgnore将把字段序列化为null，而JsonBackReference将用它的Ids序列化集合(通过应用于类的JsonIdentityInfo注释)。

 @Entity
@Table(name="DMS_Group", indexes= @Index(columnList="groupName"),
            uniqueConstraints={@UniqueConstraint(columnNames={"groupName"})})
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class,property = "groupID")
public class DMSGroupBean {

   @ManyToMany(mappedBy = "groups",fetch = FetchType.LAZY)
   @JsonManageReference
   private List<DMSDocumentClass> docClasses;

和

@Entity
@Table(name="DMS_Document_Class")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class,property = "docClassindexID")
public class DMSDocumentClass {

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "DOCCLASS_GROUP", 
    joinColumns = {@JoinColumn(referencedColumnName ="DocumentClass_Index_ID")}, inverseJoinColumns = {@JoinColumn(referencedColumnName="groupID")})
    @JsonBackReference
    private List<DMSGroupBean> groups;