jsp request问题

Java code:

if(request.getAttribute("top")==null){
request.setAttribute("top","1");
}
String topS=(String)request.getAttribute("top");
top=Integer.parseInt(topS);


报如下错：
java.lang.ClassCastException: com.opensymphony.xwork2.DefaultTextProvider
cannot be cast to java.lang.String

java.lang.ClassCastException: com.opensymphony.xwork2.DefaultTextProvider
cannot be cast to java.lang.String
at _jsp._entplist__jsp._jspService(entpList.jsp:22)
at com.caucho.jsp.JavaPage.service(JavaPage.java:61)
at com.caucho.jsp.Page.pageservice(Page.java:578)
at com.caucho.server.dispatch.PageFilterChain.doFilter(PageFilterChain.java:195)
at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:416)
at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:87)
at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:187)
at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:265)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:273)
at com.caucho.server.port.TcpConnection.run(TcpConnection.java:682)
at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:743)
at com.caucho.util.T