servlet页面代码：@每次请求时产生一个token(一般为时间戳),存于session中并随之用hidden提交，在servlet中判断接收到的token和session中的是否一致来判断是否重复提交，如果不是则重新产生一个 ? token存于session中覆盖原来的token。
@当用户返回或者刷新重复请求servlet时，servlet判断token是否一致，由于请求方没有产生新的token，所以和servlet新产生的token不一致，认为重复提交。
@当用户在请求页面刷新也就是重新在请求页面产生token，这时新的token覆盖servlet产生的token，这时token一致，认为是一个新的请求。
@请求的jsp页面代码:
<body>
????<%
???????????long?token=System.currentTimeMillis();????//产生时间戳的token
????????????session.setAttribute("token",token);????
???????????
????%>
????<form??action="isRepeat"?method="post">
????????<input?type="text"??name="username"/>
????????<input?type="text"??name="password"/>
????????<input?type="hidden"?value="<%=token?%>"?name="token"/>???<!--?作为hidden提交?-->
????????<input?type="submit"?value="提交"/>
????</form>
</body>
????<%
???????????long?token=System.currentTimeMillis();????//产生时间戳的token
????????????session.setAttribute("token",token);????
???????????
????%>
????<form??action="isRepeat"?method="post">
????????<input?type="text"??name="username"/>
????????<input?type="text"??name="password"/>
????????<input?type="hidden"?value="<%=token?%>"?name="token"/>???<!--?作为hidden提交?-->
????????<input?type="submit"?value="提交"/>
????</form>
</body>
?
@servlet页面代码：?protected?void?doPost(HttpServletRequest?req,?HttpServletResponse?resp)
????????????throws?ServletException,?IOException?{
?????????req.setCharacterEncoding("utf-8");
?????????resp.setCharacterEncoding("utf-8");
?????????resp.setContentType("text/html,charset=utf-8");
?????????String?username=req.getParameter("username");
?????????String?password=req.getParameter("password");
?????????long?token=Long.parseLong(req.getParameter("token"));
?????????long?tokenInSession=Long.parseLong(req.getSession().getAttribute("token")+"");
?????????if(token==tokenInSession){
????????????resp.getWriter().println("ok?");
????????????????????????//如果是第一次请求，则产生新的token?
????????????????????????req.getSession().setAttribute("token",?System.currentTimeMillis());
?????????????
?????????}
?????????else
?????????{
?????????????
????????????resp.getWriter().println("do?not?repeat?submit");?
?????????}
????}
?????????req.setCharacterEncoding("utf-8");
?????????resp.setCharacterEncoding("utf-8");
?????????resp.setContentType("text/html,charset=utf-8");
?????????String?username=req.getParameter("username");
?????????String?password=req.getParameter("password");
?????????long?token=Long.parseLong(req.getParameter("token"));
?????????long?tokenInSession=Long.parseLong(req.getSession().getAttribute("token")+"");
?????????if(token==tokenInSession){
????????????resp.getWriter().println("ok?");
????????????????????????//如果是第一次请求，则产生新的token?
????????????????????????req.getSession().setAttribute("token",?System.currentTimeMillis());
?????????????
?????????}
?????????else
?????????{
?????????????
????????????resp.getWriter().println("do?not?repeat?submit");?
?????????}
????}