准确的说，没看懂

http://www.cnblogs.com/chencheng/archive/2013/07/07/3161778.html

http://www.cnblogs.com/dkblog/archive/2010/12/07/1980682.html

http://www.liaoxuefeng.com/wiki/001374738125095c955c1e6d8bb493182103fac9270762a000/00138683229901532c40b749184441dbd428d2e0f8aa50e000

pdb