Cookie cookie = new Cookie("LastAccessTime",System.currentTimeMillis()+"");
cookie.setMaxAge(1*30*24*3600);//设置有效期1个月
cookie.setPath("/项目名称");//访问整个项目都带cookie

Cookie cookies[] = request.getCookies();
for(int i = 0;cookie!=null&&i<cookies.length;i++){
  if(cookies[i].getName().equals("LastAccessTime")){
   long cookieValues = Long.parseLong(cookies[i].getVlues());//将String转化为10进制Long型
   Date date = new Date(cookieValues);
   response.getWrite().print(date);
  }
}

HttpSession session = request.getSession();
session.setAttribute("name","哈哈哈哈");

HttpSession session = request.getSession();
//HttpSession session = request.getSession(false);//只获取不创建
String str = (String)session.getAttribute("name");

<seeeion-config>
  <session-timeout>20</session-timeout>  
</session-config>

HttpSession session = request.getSession();
session.invalidate();
//session.removeAttribute("XXX");//移除某个session

request.getSession();
String url1 = response.encodingURL("需要重写的地址1");
String url2 = response.encodingURL("需要重写的地址2");
PrintWriter out = response.getWriter;
out.print("<a href = '"+url1+"'>XXXX</a>");
out.print("<a href = '"+url2+"'>YYYY</a>");

<form action="/项目/xxx" method ="post" onsubmit="return dosubmit(this)">
  用户名:<input type="text" name="username"><br/>
  密码:<input type="password" name = "password"><br/>
  <input type="submit" value="提交">
</form>

<script>
  function dosubmit(obj){
   if(obj.category.value==''){
    alter("请输入");
    return false;
   }  
  }
</script>

<form action="/项目/xxx" method ="post" onsubmit="return dosubmit()">
  用户名:<input type="text" name="username"><br/>
  密码:<input type="password" name = "password"><br/>
  <input type="submit" value="提交">
</form>

<script>
  function dosubmit(){
   var iscommitted = false;
   if(!iscommitted){
    iscommitted = true;
    return true;
   }else{
    return false;  
   }
  }
</script>