class A
{
  ...
  @OneToMany()
  @JoinColumn(name="A_ID")
  /*   B_ID should be the key in this map */
  private Map<Long, B> map = new HashMap<Long, B>();
}

class B
{
  @EmbeddedId
  private CompoundId id;
}

@Embeddable
class CompoundId
{
  @Column(name = "A_ID")
  String aId;
 
  @Column(name = "B_ID")
  long bId
}

<map name="map" inverse="true" cascade="all-delete-orphan" lazy="false">
   <key>
      <column name="A_ID" />
   </key>

   <map-key type="long" column="B_ID"/>
   <one-to-many class="B" />
</map>

@OneToMany(targetEntity = B.class , cascade = CascadeType.ALL , orphanRemoval = true , fetch = FetchType.EAGER)
@JoinColumn(name = "A_ID", referencedColumnName = "A_ID")
@MapKeyColumn(name = "B_ID")
private Map<Long, B> entities = new HashMap<Long, B>();