Listener中获取HttpServletRequest

要在Listener中获取HttpServletRequest，方法其实很简单：

ServletRequestAttributes rervletRequestAttributes = (ServletRequestAttributes)RequestContextHolder.currentRequestAttributes();
HttpServletRequest request = rervletRequestAttributes.getRequest();

但是有一种情况要特别注意， 就是请求不是来自于DispatcherServlet/DispatcherPortlet，例如filter之类。

这种情况下就必须得在web.xml里加入下面的listener：

	    org.springframework.web.context.request.RequestContextListener

 不然就会得到以下错误信息：

No thread-bound request found: Are you referring to request attributes outside of an actual web request, or processing a request outside of the originally receiving thread? If you are actually operating within a web request and still receive this message, your code is probably running outside of DispatcherServlet/DispatcherPortlet: In this case, use RequestContextListener or RequestContextFilter to expose the current request.