Servlet返回信息给原Jsp无法弹出Alert信息,该怎么处理_Java Web开发

Servlet返回信息给原Jsp无法弹出Alert信息
如题，代码如下，请大侠帮忙分析:

index.jsp:

<html>
  <head>
    <title></title>
    <script type="text/javascript">
if(<%=request.getAttribute("flag")%>){
alert("申请成功!");
}
</script>

Servlet:

FurloughApply applyInfo = new FurloughApply(0,proposer,dept,applydate,starttime,lasttime,type);
FurloughApplyDao applyDao = new FurloughApplyDaoImpl();
boolean flag = applyDao.addApply(applyInfo);
request.setAttribute("flag", flag);
if(flag == true){
request.getRequestDispatcher("index.jsp").forward(request, response);
}else{
request.getRequestDispatcher("jsp/add.jsp").forward(request, response);
}
------解决思路----------------------
if(<%=request.getAttribute("flag")%>){
alert("申请成功!");
}

request接收的是object
------解决思路----------------------
request.getParameter("flag")

session.getAttribute("flag")
------解决思路----------------------


if(<%=request.getAttribute("flag")%>=="true"){
alert("申请成功!");
}

试试
------解决思路----------------------
if(<%=request.getAttribute("flag")%>){
你这样写，其实也是拼接
------解决思路----------------------
写在JS里，把JS放在页面最上面。
------解决思路----------------------


<% if(request.getAttribute("flag")!=null){%>
<script type="text/javascript">
alert("申请成功!");
</script>
<% } %>