参考：
http://blog.csdn.net/github_27109687/article/details/71968662 Jmeter接口测试+压力测试
http://blog.csdn.net/sd4015700/article/details/50348978
http://www.cnblogs.com/imyalost/p/6802173.html jmeter函数助手对话框之参数详解
http://www.cnblogs.com/fnng/archive/2012/12/27/2836506.html JMeter基础之--元件的作用域与执行顺序
https://www.cnblogs.com/puresoul/p/4833841.html Jmeter组件执行顺序与作用域