浅谈Servlet的Cookie和Session机制

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 SetCookieServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.创建Cookie对象
        //首先需要一个cookie对象,这里我们需要两个cookie对象，一个来存储用户名（username——java），一个来存储密码（pwd——javas）
        Cookie username = new Cookie("uesrname","java");
        Cookie pwd = new Cookie("pwd","javas");
        //当我们创建好两个cookie对象之后，就可以对这两个对象进行一系列操作
        //比如：设置他的过期时间，这里我们将username的过期时间设置为永久
        username.setMaxAge(-1);
        //密码pwd的过期时间设置为一分钟,注意他的过期时间是以秒为单位
        pwd.setMaxAge(60);
        //2.将 Cookie 对象关联到response上
        resp.addCookie(username);
        resp.addCookie(pwd);

        //显示给用户部分的信息
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
        //然后写入响应给客户端的内容
        PrintWriter writer = resp.getWriter();
        writer.println("<h1>Cookie 设置成功</h1>");

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

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 GetCookieServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //读取Cookie的信息
        //因为客户端的cookie可能会有多个，所以我们使用数组来接收,注意：cookie是从request获取的
        Cookie[] cookies = req.getCookies();
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        PrintWriter writer = resp.getWriter();
        //然后读取cookie的内容
        for (Cookie item: cookies
             ) {
            writer.println(String.format("<h1>Cookie key: %s,Cookie value: %s</h1>",item.getName(),item.getValue()));
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

public class SessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //关于 session 的读写
        //1.先获取到session到对象
        HttpSession session = req.getSession();

        //2.得到session的属性
        //2.1获取到session的ID
        String sessionID = session.getId();


        //返回响应信息
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        PrintWriter writer = resp.getWriter();
        writer.println("<h1>欢迎访问页面</h1>");
        //输出sessionID
        writer.println(String.format("<h3>SessionID : %s </h3>",sessionID));
        //输出session的创建时间，因为session的创建时间是一个时间戳，所以我们需要将其强转成我们能看得懂的时间
        writer.println(String.format("<h3>Session创建时间: %s</h3>",new Date(session.getCreationTime())));
        //输出session的最后访问时间
        writer.println(String.format("<h3>Session的最后访问时间: %S</h3>",new Date(session.getLastAccessedTime())));
        
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}