@Configurable
@XStreamAlias("Employer")
@Entity
public class Employer {

        @Id
       @GeneratedValue(strategy = GenerationType.AUTO)
         private Long id;

        private Dept dept;
        // getter, setter
}

@Configurable
@XStreamAlias("Dept")
@Entity
public class Dept {

        @Id
       @GeneratedValue(strategy = GenerationType.AUTO)
         private Long id;
        ...........
   @Embedded
   private List<Employee> empList = new ArrayList<Employee>();
        // getter, setter
        ............
}

@Configurable
@XStreamAlias("Employee")
@Embeddable
@Entity
public class Employee {
                  ..................
}