说的很模糊，看下这个是否需要http://wenku.baidu.com/link?url=4kZCAq87BmnGJcjYDZnn751D2qLjzrHj0kKy9VhLSjraFEu0OB9_RJQYB2Z-gm8jdR1dxCT0Kq8NbvI3OCg0ei_vTidLO8v4TOUucDB_xsG
