servlet类：
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LastTimeServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
Cookie[] cookies = req.getCookies();//拿到Cookies集合
String msg="";
Cookie cook=null;
Date date = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String newDate = sdf.format(date);//将当前的时间格式化
for(Cookie c:cookies){
String name = c.getName();
//非首次访问
if("lastTime".equals(name)){
cook=c;
msg=c.getValue();//拿到cook里的日期
c.setValue(newDate);//将当前访问日期设置进去
}
}
//首次访问
if("".equals(msg)){
msg="首次访问";
cook=new Cookie("lastTime",newDate);//将当前时间是指进去
}
cook.setMaxAge(199999999);
resp.addCookie(cook);//将cook放到响应对象里
req.setAttribute("msg", msg);
req.getRequestDispatcher("/success.jsp").forward(req, resp);//转发
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
doGet(req, resp);
}
}
web页面
index页面（为了方便只写bodyti,请自行补全）
<body>
<form action="/JavaMailTest/lastTime" method="post">
<input type="submit" value="submit"/>
</form>
</body>
success页面
<body>
上次访问的时间是：<%=request.getAttribute("msg") %>
</body>
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>JavaMailTest</display-name>
<servlet>
<servlet-name>LastTimeServlet</servlet-name>
<servlet-class>LastTimeServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LastTimeServlet</servlet-name>
<url-pattern>/lastTime</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>