ServletRequest和HttpServletRequest的联系与区别
HttpServletRequest和ServletRequest都是接口
HttpServletRequest继承自ServletRequest
HttpServletRequest比ServletRequest多了一些针对于Http协议的方法。如getHeader(String name)，getMethod() ，getSession() 等等。
他们对应的实现类：
javax.servlet.ServletRequestWrapper (implements javax.servlet.ServletRequest)
javax.servlet.http.HttpServletRequestWrapper (implements javax.servlet.http.HttpServletRequest)?
