CompositeIdAssociations.java

@Entity
public class PersonAddress  implements Serializable {

    @Id
    @ManyToOne
    private Person person;

    @Id
    @ManyToOne()
    private Address address;

    public PersonAddress() {}

    public PersonAddress(Person person, Address address) {
        this.person = person;
        this.address = address;
    }

    public Person getPerson() {
        return person;
    }

    public void setPerson(Person person) {
        this.person = person;
    }

    public Address getAddress() {
        return address;
    }

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

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        PersonAddress that = (PersonAddress) o;
        return Objects.equals(person, that.person) &&
                Objects.equals(address, that.address);
    }

    @Override
    public int hashCode() {
        return Objects.hash(person, address);
    }
}

@Entity
public class Person  {

    @Id
    @GeneratedValue
    private Long id;

    @NaturalId
    private String registrationNumber;

    public Person() {}

    public Person(String registrationNumber) {
        this.registrationNumber = registrationNumber;
    }

    public Long getId() {
        return id;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Person person = (Person) o;
        return Objects.equals(registrationNumber, person.registrationNumber);
    }

    @Override
    public int hashCode() {
        return Objects.hash(registrationNumber);
    }
}

@Entity
public class Address  {

    @Id
    @GeneratedValue
    private Long id;

    private String street;

    private String number;

    private String postalCode;

    public Address() {}

    public Address(String street, String number, String postalCode) {
        this.street = street;
        this.number = number;
        this.postalCode = postalCode;
    }

    public Long getId() {
        return id;
    }

    public String getStreet() {
        return street;
    }

    public String getNumber() {
        return number;
    }

    public String getPostalCode() {
        return postalCode;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Address address = (Address) o;
        return Objects.equals(street, address.street) &&
                Objects.equals(number, address.number) &&
                Objects.equals(postalCode, address.postalCode);
    }

    @Override
    public int hashCode() {
        return Objects.hash(street, number, postalCode);
    }
}