JPA how to make composite Foreign Key part of composite Primary Key

@Embeddable
public class EventID {
    public int eventID;
    public int sourceID;
}

@Entity
public class Event {
    @EmbeddedId
    public EventID id;

    @OneToMany(mappedBy="event")
    public Collection<Meeting> meetings;
}

@Embeddable
public class MeetingID {
    public EventID eventID; // corresponds to ID type of Event
    public int meetingID;
}

@Entity
public class Meeting {
    @EmbeddedId
    public MeetingID id;

    @MapsId("eventID")
    @JoinColumns({
        @JoinColumn(name="EventID", referencedColumnName="EventID"),
        @JoinColumn(name="SourceID", referencedColumnName="SourceID")
    })
    @ManyToOne
    public Event event;
}

Discussed in JPA 2.1 spec, section 2.4.1.

@Entity
public class Event {

    @EmbeddedId
    private EventId id;

    @OneToMany(mappedBy = "event")
    private List<Meeting> meetings = new ArrayList<>();
}

@Embeddable
public class EventId implements Serializable {

    @Column(name = "EventID")
    private Long eventId;

    @Column(name = "SourceID")
    private Long sourceId;

    //implements equals and hashCode
}

@Entity
public class Meeting {

    @EmbeddedId
    private MeetingId id; 

    @MapsId("eventId")
    @JoinColumns({
        @JoinColumn(name="EventID", referencedColumnName="EventID"),
        @JoinColumn(name="SourceID", referencedColumnName="SourceID")
    })
    @ManyToOne
    private Event event;
}

@Embeddable
public class MeetingId implements Serializable {

    @Column(name = "MeetingID")
    private Long meetingId;

    private EventId eventId;

    //implements equals and hashCode
}

You may want to take a look at a similar question for more details.