关于history.back()使request和session失效问题

request.setAttribute("updateLogisticsSingleSuccess","<script language='javascript'>alert('请先提交物流单！');</script>");
response.setContentType("text/html;charset=utf-8");
response.setCharacterEncoding("utf-8");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println("  <BODY>");
out.println("<script language='JavaScript'>alert(\"请先提交物流单！\");history.back();</script>");
out.println("  </BODY>");
out.println("</HTML>");
out.flush();
out.close();
页面上这样提取<s:iterator value="#session.PurchaseOrderDetailsBylmlcpmpnNumberInformation">
但是 后面的request不能覆盖前面的一个request  还是一起弹出来了 求助...