1、说明：如何在Struts2 中创建 servlet 的域空间

2、实现方法一：

      用 ServletActionContext 类访问 Servlet的api。

public String testServletAPI(){
		//访问request
		HttpServletRequest request = ServletActionContext.getRequest();

		//访问session  对session进行了二次封装
		Map sessionMap = ServletActionContext.getContext().getSession();

		//访问application
		ServletContext servletContext = ServletActionContext.getServletContext();
		return "";
}

      通过同时实现 ServletContextAware，SessionAware，ServletRequestAware 三个接口

public class ServletAction extends ActionSupport implements ServletContextAware,SessionAware,ServletRequestAware{
	private HttpServletRequest request;
	private Map sessionMap;
	private ServletContext servletContext;

	public String testServletAPI2(){
		System.out.println(this.servletContext);
		System.out.println(this.sessionMap);
		System.out.println(this.request);
		return "";
	}

	public void setServletContext(ServletContext context) {
		this.servletContext = context;
	}
	public void setSession(Map<String, Object> session) {
		this.sessionMap = session;
	}
	public void setServletRequest(HttpServletRequest request) {
		this.request = request;
	}
}