Struts2之ActionContext的初始化时机错误 导致空指针

@SuppressWarnings("serial")public abstract class AbstractParamAction extends ActionSupport{public ActionContext actionContext = ActionContext.getContext();public HttpServletRequest request = (HttpServletRequest) actionContext.get(ServletActionContext.HTTP_REQUEST);public HttpServletResponse response = (HttpServletResponse) actionContext.get(ServletActionContext.HTTP_RESPONSE);//public ServletContext  application = (ServletContext)actionContext.getApplication();public HttpSession session = request.getSession();}

/** *  */package com.wonders.stpt.marquee.action;import org.apache.struts2.convention.annotation.Action;import org.apache.struts2.convention.annotation.Namespace;import org.apache.struts2.convention.annotation.ParentPackage;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.beans.factory.annotation.Qualifier;import org.springframework.context.annotation.Scope;import org.springframework.stereotype.Controller;import com.wonders.stpt.innerWork.action.AbstractParamAction;import com.wonders.stpt.marquee.service.MarqueeService;import com.wonders.stpt.util.ActionWriter;/**  * @ClassName: MarqueeAction  * @Description: TODO(这里用一句话描述这个类的作用)  * @author zhoushun  * @date 2014年2月28日 下午1:58:40  *   */@ParentPackage("struts-default")@Namespace(value="/marquee")@Controller("marqueeAction")@Scope("prototype")public class MarqueeAction extends AbstractParamAction{/** *  */private static final long serialVersionUID = 4787537184825647031L;private ActionWriter aw = new ActionWriter(response);private MarqueeService service;public MarqueeService getService() {return service;}@Autowired(required=false)public void setService(@Qualifier("marqueeService")MarqueeService service) {this.service = service;}@Action(value="getMarquee")public String getMarquee(){aw.writeJson(this.service.getMsg());return null;}}

原来 action 中 使用的都是 多例模式，每次初始化action都是在 一个请求发起后，故actionContext 中均有 request，response等值。

但改为单例模式后，自动在spring加载时初始化，此时actionContext中，由于未发生用户请求，request，response 均为空。

若要使用单例模式，就只能在具体方法中获得request等其他对象。