便于理解,大体流程如下: 参考资料: http://jingyan.baidu.com/article/95c9d20d92a74eec4f75614f.html http://www.cnblogs.com/ttltry-air/archive/2012/08/20/2647898.html http://www.51testing.com/html/89/467989-3578434.html