http://wenku.baidu.com/link?url=gBNVeERTKVZBRIH-Gvh1xvrFWCbTs1rarDc_QkSjt7F4meSPmxBJAaEn2dUEjZrVV4HpeIUG2dFubJVX1U27Khz2e8mEDbVgdD7Z5_g26V3
http://jingyan.baidu.com/article/9225544699b657851648f49b.html
http://blog.csdn.net/h3c4lenovo/article/details/7917293