<body onload="loadFun();">
<input type=hidden name=thisPageHasBeenSubmitted >
<form name="form1" method="post" action="a2.html" >
<input type="text" name="txt">
<input type="submit" name="submit" value="submit" onclick="document.all.thisPageHasBeenSubmitted.value=1;"> 
</form>
</body>
<script language=javascript>
function loadFun()
{
if(document.all.thisPageHasBeenSubmitted.value)
  {
  alert("页面己被submit,资料过期")
  history.forward();
  }}
</script>