http://wenku.baidu.com/link?url=kxEGoy6KZYLky0Xtm5uEBEdtIUXcXk3imFdwZ4vyOYmZOUhGXbZ3hKxNUaXcztYl4t9g4Bopti9lT5g2nDH0b-H8tNhzYaYc69HIsay0R_y
https://segmentfault.com/q/1010000002800546
http://jingyan.baidu.com/article/15622f2416c17efdfcbea5e9.html
原文：http://www.cnblogs.com/leaves201601/p/6437793.html