可参考http://wenku.baidu.com/link?url=AfnDX70QSA0u0hrwuUace6QyVgRcogACQqG9PUu1sq3kq6MOHQS7ZtvZjTgy7g96nCnHdO_u_9Mlz2dsyJNuNan1w4J5joic0_6kn17Ss0W