实现客户端与服务端的维持

需求：当客户端浏览器第一次访问Servlet时响应“您好，欢迎您第一次访问！”，第二次访问时响应“欢迎您回来！”。

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class WelcomServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req, resp);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取cookie
        Cookie[] cookies = req.getCookies();
        boolean flag = false;
        if (cookies != null){
            for (Cookie cookie:cookies){
                if ("welcome".equals(cookie.getName())){
                    flag = true;
                    break;
                }
            }
        }
        resp.setContentType("text/plain;charset=utf-8");
        PrintWriter printWriter = resp.getWriter();
        if(flag){
            printWriter.println("欢迎回来");
        }else{
            printWriter.println("您好，欢迎第一次访问");
            Cookie cookie = new Cookie("welcome","welcome");
            cookie.setMaxAge(60);
            resp.addCookie(cookie);
        }
    }
}

Cookie总结

Cookie对于存储内容是基于明文的方式存储的，所以安全性很低。不要在Cookie中存放敏感数据。在数据存储时，虽然在Servlet4.0中Cookie支持中文，但是建议对Cookie中存放的内容做编码处理，也可提高安全性。