Components can be used to implement the object-oriented concept of composition.

This kind of relation can of course also be designed using a relation to an entity. So the question is, how to choose between entity relations versus and composition?

Let’s have a look at a first example and then we will work out the criteria to choose the correct approach.

A person has an address component.

Person class. 

import javax.persistence.Entity;
@Entity
public class Person{

   private Address address;

Address class. 

import javax.persistence.Embeddable;

@Embeddable
public class Address {
    private String street;

Collections of components are supported as well. A person might have a collection of former addresses.

Person class. 

import javax.persistence.Entity;
@Entity
public class Person{
   private Address address;

    @ElementCollection
    @CollectionTable(name = "person_former_addresses",
      joinColumns = @JoinColumn(name = "person_fk"))
   private Set<Address> formerAddresses = new HashSet<Address>();