无法编写JSON：无限递归

Question

当我在Postman或Browser中运行查询时，我得到StackOverflow递归错误。

当我跑步时说：

。w.s.m.s.DefaultHandlerExceptionResolver：无法编写JSON：无限递归（StackOverflowError）;嵌套的异常是com.fasterxml.jackson.databind.JsonMappingException：无限递归（StackOverflowError）

这里是模型类别：

@Entity 
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @NotNull
    private String title;
    @NotNull
    private String description;
    @NotNull
    private double price;
    @OneToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "category_id", nullable = false)
    private Category category;
    private boolean isSealed;
    @OneToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "currency_id", nullable = false)
    private Currency currency;
    @OneToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "user_id", nullable = false)
    private User user;
    @Nullable
    @OneToMany(mappedBy = "product",
            cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Images> images;
    private Date createdDate = new Date();
    @OneToOne(fetch = FetchType.LAZY,
            cascade = CascadeType.ALL,
            mappedBy = "product")
    private View view;
    @OneToOne(fetch = FetchType.LAZY,cascade=CascadeType.ALL)
    @JoinColumn(name="type_id")
    private Type type;
    private Long viewCount; }

@Entity public class Images{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String imagePath;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "product_id")
    private Product product; }

@Entity public class User implements UserDetails, Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @NotEmpty
    private String fullName;
    @NotEmpty
    @Email
    @Column(unique = true)
    private String email;
    @NotNull
    @Column(unique = true)
    private int phoneNumber;
    @NotEmpty
    @Size(min = 5)
    private String password;
    private Date createAt = new Date();
    @Nullable
    private String picPath;
    @Nullable
    private String token;
    @ManyToMany
    @JoinTable(name = "user_roles", joinColumns = {@JoinColumn(
            name = "user_id")},
            inverseJoinColumns = {@JoinColumn(name = "role_id")})
    private List<Role> roles;
    @OneToOne(fetch = FetchType.LAZY,
            cascade = CascadeType.ALL,
            mappedBy = "user")
    private Product product;
    @OneToOne(fetch = FetchType.LAZY,
    cascade = CascadeType.ALL,
    mappedBy = "user")
    private View view; }

@Entity 
public class Currency{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String code;
    private String currency;
    private String region_country;
    @OneToOne(mappedBy = "currency", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Product product; }

@Entity 
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String imagePath;
    @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY,
    mappedBy = "category")
    private Product product;
    @OneToMany(mappedBy = "category", fetch = FetchType.LAZY,
            cascade = CascadeType.ALL)
    private Set<Brand> brands; }

@Entity public class Brand {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "category_id", nullable = false)
    private Category category; }

@Entity public class View {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @OneToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "user_id", nullable = false)
    private User user;
    @OneToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "product_id", nullable = false)
    private Product product; }

@Entity public class Type {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @NotNull
    private String name;
    @OneToOne(fetch = FetchType.LAZY,
            cascade = CascadeType.ALL,
            mappedBy = "type")
    private Product product; }

    @Id
    private String role;
    @ManyToMany(mappedBy = "roles")
    private List<User> users; 
}

Answer 1

您的数据模型中有周期。例如，Product保持Images，Images指向Products。

这在面向对象的世界中有效，因为只有指针引用存储在这些字段中。

然而，序列化时，实际对象被写为json文本。您的Product打印Images对象，然后又打印Product对象，然后再次打印Image对象，依此类推。

[您需要决定如何表示json，将数据库模型映射到简单的普通Java对象，并将其用于序列化。这些POJO通常称为视图模型或传输对象。

Answer 2

您的多个实体彼此之间都有彼此。例如，Product的对象为User，User的对象为Product。

要解决这个问题，您必须写

@JsonBackReference(value = "user-product")
private User user;

在Product类中，和

@JsonManagedReference(value = "user-product")
private Product product;

在user类中。在每个领域以及彼此调用的每个类中执行此操作。

另外，请查看此JPA: Having lists on both ends without infinite loop