struts2里，ajax执行java方法，怎么得到request

dwr实现ajax
getTypeList()方法供ajax调用，可是得不到request，执行时页面上就弹出一个alert，上面只显示ERROR
要怎么得到request

Java code:
public class FileUploadAction extends ActionSupport {
public HttpServletRequest request;
public String dburl;

public List getTypeList() {
System.out.println(1);//这句能打印，然后就啥都没了
request = ServletActionContext.getRequest();//走到这就停了
System.out.println(2);
dburl = request.getSession().getServletContext().getRealPath("/");

return null;
}
}

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return 要返回的list

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PrintWrite pw=response.getWrite();
pw.write("需返回的数据")

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引用

return 要返回的list

和返回啥没关系，没走到return

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/** 在dwr中取session,request,response */
WebContext webContext = WebContextFactory.get(); 
HttpSession session = webContext.getSession();
HttpServletRequest request=webContext.getHttpServletRequest();
HttpServletResponse response=webContext.getHttpServletResponse();

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引用

/** 在dwr中取session,request,response */
WebContext webContext = WebContextFactory.get(); 
HttpSession session = webContext.getSession();
HttpServletRequest request=webContext.getHttpServletRequest()