The request lifetime scope cannot be created because the HttpContext is not available

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;