项目中应用了Autofac，在Global轮询处理Job的时候，需要获取现有得Service，而这些Service已经通过Autofac进行了配置，所以理所应当的用下面的代码去获取了。
DependencyResolver.Current.GetService<ClinicalCaseService>();
结果出现问题了，直接抛出错误“The request lifetime scope cannot be created because the HttpContext is not available”。
结果疯狂的stackoverflow（地址：https://stackoverflow.com/questions/21804857/autofac-the-request-lifetime-scope-cannot-be-created-because-the-httpcontext-i），查找解决方案。
因为在AutofacDependencyResolver.Current内部GetService的时候需要HttpContext，所以会直接抛出错误。
解决方案：
1，autofac
var resolver = new AutofacWebApiDependencyResolver(container);
???????????GlobalConfiguration.Configuration.DependencyResolver = resolver;
2，获取Service
ClinicalCaseService = GlobalConfiguration.Configuration.DependencyResolver.GetService(typeof (ClinicalCaseService)) as ClinicalCaseService;
The request lifetime scope cannot be created because the HttpContext is not available
原文地址：http://www.cnblogs.com/icebutterfly/p/7660270.html