@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name = "TYPE", discriminatorType = DiscriminatorType.STRING)
@org.hibernate.annotations.ForceDiscriminator
@Table(name = "Components")
public class Component implements Serializable {

@Id
    @GeneratedValue(generator = "sequence")
    @GenericGenerator(name = "sequence", strategy = "sequence",
    parameters = {
        @Parameter(name = "sequence", value = "Components_SEQUENCE")
    })
    protected Long id;

getter/setter

}

===============
@Entity
@Table(name = "Documents")
@DiscriminatorValue("Document")
public class Document extends Component {

    @Column
    private String content;
getter/setter
}