JPA 实体在转换为 JSON 时会出现 stackoverflow 错误

Question

我正在使用 JSON 和 JPA，并且有主要方法来对我的对象进行一些测试。

每当我尝试将 Java 实体转换为 JSON 字符串时，都会出现堆栈溢出错误

String jsonString = gson.toJson(cus1)

如果我在这种情况下使用常规 POJO 作为 DTO，则不会出现错误。但是，当我使用实体类时，为什么会出现堆栈溢出错误？

@Entity

@Table(name = "Customers")

@XmlRootElement

@NamedQueries({

    @NamedQuery(name = "Customer.findAll", query = "SELECT c FROM Customer c")

    , @NamedQuery(name = "Customer.findById", query = "SELECT c FROM Customer c WHERE c.id = :id")

    , @NamedQuery(name = "Customer.findByName", query = "SELECT c FROM Customer c WHERE c.name = :name")

    , @NamedQuery(name = "Customer.findByAge", query = "SELECT c FROM Customer c WHERE c.age = :age")})

public class Customer implements Serializable {

private static final long serialVersionUID = 1L;

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

private Integer id;

private String name;

private int age;

@JoinColumn(name = "city", referencedColumnName = "id")

@ManyToOne(optional = false)

private City city;

//getters, setters and constructor

Answer 1

该错误与 City 序列化 Customer 和 Customer 再次序列化城市有关，导致StackOverflowError.如果您没有在Customer实体中使用城市对象，只需在 json 序列化期间忽略该字段。@XmlRootElementpublic class Customer {&nbsp; &nbsp; @XmlTransient&nbsp; &nbsp; private Set<City> cities;}反之亦然，@XmlTransient在private City city;现场使用。