转载自：http://hi.baidu.com/%CE%E2_%F0%A9/blog/item/952543009a067edc277fb5b7.html
获取HttpServletRequest / HttpSession / ServletContext / HttpServletResponse对象
方法一，通过ServletActionContext.类直接获取：
public String rsa() throws Exception{
HttpServletRequest request = ServletActionContext.getRequest();
ServletContext servletContext = ServletActionContext.getServletContext();
request.getSession()
HttpServletResponse response = ServletActionContext.getResponse();
return "scope";
}
方法二，实现指定接口，由struts框架运行时注入：
public class HelloWorldAction implements ServletRequestAware, ServletResponseAware, ServletContextAware{
private HttpServletRequest request;
private ServletContext servletContext;
private HttpServletResponse response;
public void setServletRequest(HttpServletRequest req) {
this.request=req;
}
public void setServletResponse(HttpServletResponse res) {
this.response=res;
}
public void setServletContext(ServletContext ser) {
this.servletContext=ser;
}
}