Session

文章目录

- 1.Session基本介绍
- - - 1.Session有什么用?
    - 2.Session基本原理
    - 3.Session可以做什么？
    - 4.如何理解Session？
    - 5. Session基本使用
- 2.Session底层机制
- - - 1.示意图
    - 2.创建session底层机制
    - - 1.有sessionid，但没session对象
      - 1.由于访问了jsp的主页面，会导致jsp创建一个sessionid，重新发布之后会将session对象删除
        2.代码实例
      - 2.有sessionid，有session对象
      - 1.刚才已经创建了一个新的session对象并绑定了一个新的sessionid，返回给浏览器，所以现在的浏览器既有sessionid又有session对象
        2.代码实例（还是刚才的代码）
      - 3.没有sessionid，没有session对象
      - 1.更换一个浏览器，此时这个浏览器并没有携带这个服务器的sessionid
        2.代码实例（还是刚才的代码）
    - 3.读取session底层机制
- 3.Session的生命周期
- - - 1.基本说明
    - - 一个浏览器同一时间只能有一个session！！！
    - 2.设置指定过期时间
    - - 1.CreateSession2.java
      - 2.readSession2.java
      - 3.结果演示
    - 3.删除session
- 4.Session作业
- - - 1.login.html
    - 2.error.html
    - 3.LoginCheckServlet.java
    - 4.ManageServlet.java
    - 5.结果展示
- 5.Session小结
- - - 关于getSession的理解

1.Session基本介绍

1.Session有什么用?

2.Session基本原理

3.Session可以做什么？

4.如何理解Session？

5. Session基本使用

2.Session底层机制

1.示意图

2.创建session底层机制

1.有sessionid，但没session对象

1.由于访问了jsp的主页面，会导致jsp创建一个sessionid，重新发布之后会将session对象删除

2.代码实例

package session;import sun.security.jgss.HttpCaller;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.DataOutput;
import java.io.IOException;
import java.io.PrintWriter;/*** @author 孙显圣* @version 1.0*/
@WebServlet(urlPatterns = "/createSession")
public class CreateSession extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//获取session,并放值HttpSession session = req.getSession();session.setAttribute("session", "hello");resp.setContentType("text/html;charset=utf-8;");PrintWriter writer = resp.getWriter();writer.print("<h1>session设置成功</h1>");//关闭writer.flush();writer.close();}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

2.有sessionid，有session对象

1.刚才已经创建了一个新的session对象并绑定了一个新的sessionid，返回给浏览器，所以现在的浏览器既有sessionid又有session对象

2.代码实例（还是刚才的代码）

3.没有sessionid，没有session对象

1.更换一个浏览器，此时这个浏览器并没有携带这个服务器的sessionid

2.代码实例（还是刚才的代码）

3.读取session底层机制

package session;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;/*** @author 孙显圣* @version 1.0*/
@WebServlet(urlPatterns = "/readSession")
public class readSession extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//读取sessionHttpSession session = req.getSession();Object session1 = session.getAttribute("session");//先判断一下是不是为nullif (session1 != null) {String res = (String) session1;resp.setContentType("text/html;charset=utf-8;");PrintWriter writer = resp.getWriter();writer.print("<h1>"+ res +"</h1>");//关闭writer.flush();writer.close();}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

3.Session的生命周期

1.基本说明

一个浏览器同一时间只能有一个session！！！

2.设置指定过期时间

1.CreateSession2.java

package session;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;/*** @author 孙显圣* @version 1.0*/
@WebServlet(urlPatterns = "/createSession2")
public class CreateSession2 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//创建sessionHttpSession session = req.getSession();session.setAttribute("name", "lihua");//设置生命周期session.setMaxInactiveInterval(30);resp.setContentType("text/html;charset=utf-8;");PrintWriter writer = resp.getWriter();writer.print("<h1>session设置成功</h1>");//关闭writer.flush();writer.close();}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

2.readSession2.java

package session;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;/*** @author 孙显圣* @version 1.0*/
@WebServlet(urlPatterns = "/readSession2")
public class readSession2 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//读取sessionHttpSession session = req.getSession();Object name = session.getAttribute("name");//一定要判断不是空再返回if (name != null) {String res = (String) name;resp.setContentType("text/html;charset=utf-8;");PrintWriter writer = resp.getWriter();writer.print("<h1>"+ res +"</h1>");//关闭writer.flush();writer.close();}else {resp.setContentType("text/html;charset=utf-8;");PrintWriter writer = resp.getWriter();writer.print("<h1>该session不存在</h1>");//关闭writer.flush();writer.close();}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

3.结果演示

60秒后

3.删除session

package session;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;/*** @author 孙显圣* @version 1.0*/
@WebServlet(urlPatterns = "/deleteSession")
public class deleteSession extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//获取session,并设置立即过期（删除session）HttpSession session = req.getSession();session.invalidate();resp.setContentType("text/html;charset=utf-8;");PrintWriter writer = resp.getWriter();writer.print("<h1>session删除成功</h1>");//关闭writer.flush();writer.close();}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

4.Session作业

1.login.html

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body>
<h1>用户登录界面</h1>
<form action="check" method="get">用户名：<input type="text" name="username"><br>密码：<input type="password" name="password"><br><input type="submit" value="登录">
</form>
</body>
</html>

2.error.html

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body>
<h1>登录失败</h1><br>
<a href="login.html">点击返回重新登录！</a>
</body>
</html>

3.LoginCheckServlet.java

package session;import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;/*** @author 孙显圣* @version 1.0*/
@WebServlet(urlPatterns = "/check")
public class LoginCheckServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//获取用户名和密码String username = req.getParameter("username");String password = req.getParameter("password");//进行验证if (password.equals("666666")) {//验证成功则设置sessionHttpSession session = req.getSession();session.setAttribute("username",username);//重定向到欢迎页面resp.sendRedirect("ManageServlet");}else {resp.sendRedirect("error.html");}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

4.ManageServlet.java

package session;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;/*** @author 孙显圣* @version 1.0*/
@WebServlet(urlPatterns = "/ManageServlet")
public class ManageServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//根据session中的信息判断是否是管理员HttpSession session = req.getSession();Object state = session.getAttribute("username");//如果是空的，则说明不是管理员if (state == null) {resp.sendRedirect("error.html");}String name = (String) state;resp.setContentType("text/html;charset=utf-8;");PrintWriter writer = resp.getWriter();writer.print("<h1>用户管理页面</h1><br>");writer.print("<h3>欢迎你 管理员" + name +"</h3><br>");}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

5.结果展示

5.Session小结

关于getSession的理解

一个浏览器同时只能有一个session
注意，此时只要session不过期，那么这个浏览器每次请求服务的时候都会带上这个sessionid
首先会判断浏览器是否有sessionid
没有sessionid则会在浏览器端创建session对象并且将sessionid响应给浏览器（立即生效）
有sessionid则会判断服务器端是否有session对象
如果有session对象则直接使用
如果没有session对象则创建新的session对象并将新的sessionid响应给浏览器（立即生效）
这里立即生效的解释是，只要设置了session，就算进行了请求转发了，并没有进行第二次请求，那么转发到的那个servlet是可以立即读取到这个session的