线程“主”javax.persistence.PersistenceException 中的异常：org.hibernate.InstantiationException：实体没有默认构造函数：[重复]

Question

嗨，我是休眠新手。每当我试图从 MySQL 5.5 检索数据时，它都会抛出异常 Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.InstantiationException: No default constructor for entity:

但是当我尝试将数据保存在 sql 表中以使其正常工作时。 我也找到了这个problem 的解决方案，但它仍然显示相同的错误。

Answer 1

确保您的实体中有无参数构造函数

@Entity
@Table(name = "employee")
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer id;

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

    @Column(name="age")
    private Integer age;

    // A default constructor, one without agruments
    public Employee() {
    }


    // A constructor with agruments
    public Employee(Integer id, String name, Integer age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

   }