public class A implements Serializable {
    private static final long serialVersionUID = -1317006094950982121L;
    //其余属性及get、set方法省略
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToMany (cascade = {CascadeType.REFRESH, CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE}, fetch=FetchType.LAZY)
    private List<B> b = new ArrayList<B>();
}

public class B implements Serializable {
    private static final long serialVersionUID = -1317006094950982121L;
    //其余属性及get、set方法省略
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    //注：A中单向一对多配置，B中不配置A属性
}