5.10. 将实体 Bean 迁移到 JPA

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
// User is a keyword in some SQL dialects!
@Table(name = "MyUsers")
public class MyUser {
    @Id
    @GeneratedValue
    private Long id;

    @Column(unique = true)
    private String username;
    private String firstName;
    private String lastName;

    public Long getId() {
        return id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

<persistence version="2.1"
      xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="
        http://xmlns.jcp.org/xml/ns/persistence
        http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
  <persistence-unit name="my-unique-persistence-unit-name">
    <properties>
      // properties...
    </properties>
  </persistence-unit>
</persistence>