@Entity
@Table(name="USER")
public class User implements Serializable {
  ...
  @Id
  @Column(name="ID_USER")
  private String idUser;

  @OneToMany(mappedBy="user", cascade=CascadeType.PERSIST)
  private List<Address> address;

  public List<Address> getAddress() {
     return this.address;
  }

  public void setAddress(List<Address> address) {
     this.address = address;
  }

  public Address addAddress(Address address) {
     getAddress().add(address);
     address.setUser(this);

     return address;
  }

  public Address removeAddress(Address address) {
     getAddress().remove(address);
     address.setUser(null);

     return address;
  }
  ...
}

@Entity
@Table(name="ADDRESS")
public class Address implements Serializable {
    ...
   @EmbeddedId
   private AddressPK id;
   
    @ManyToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name="ID_USER", insertable=false, updatable=false, nullable=false)
    private User user;

    public User getUser() {
        return this.user;
    }

    public void setUser(User user) {
        this.user = user;
    }
}

@Embeddable
public class AddressPK implements Serializable {
   ...
   @Column(name="ID_USER", insertable=false, updatable=false)
   private String idUser;
   ...
}

User u = new User();
u.setAddress(new ArrayList<Address>());

u.set...

Address a1 = new Address();
a1.set...
u.addAddress(a1);

Address a2 = new Address();
a2.set...
u.addAddress(a2);

entityManager.persist(u);