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Cookies and sessions

2022-06-12 09:01:00 【continueLR】

Chapter one ：cookie And session Use

1.cookie Use

1： stay index.jsp Make a login form as login request

 <h1> Sign in </h1>
  <form action="login" method="post">
     user name :<input type="text" name="username" value="${unamecookie}"><br>
     password ：<input type="password" name="pass"><br>
    <input type="submit" value=" Sign in ">
  </form>

2： establish servlet Processing class processing login request

package servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(urlPatterns = "/login")
public class loginServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // Answer the parameters 
        String username = req.getParameter("username");
        String pass = req.getParameter("pass");
        // Write logic ： Right or wrong 
        if ("admin".equals(username)&&"123456".equals(pass)){
            // Login successful 
            resp.sendRedirect("success.jsp");
        }else{
            // Login failed 
            //1. Create in the background cookie
            Cookie cookie = new Cookie("uname",username);
            //2. Back to the front end 
            resp.addCookie(cookie);
            resp.sendRedirect("index.jsp");
        }
    }
}

3： Front end use cookie

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
  <%
    Cookie[] cookies = request.getCookies();
    String value="";
    if (cookies.length>0){// This if Judge to avoid errors caused by traversing empty data 
      for (Cookie cookie : cookies) {// Traverse cookies Array 
        if (cookie.getName().equals("uname")){
          value = cookie.getValue();
          break;
        };
      }
    }
    pageContext.setAttribute("unamecookie",value);
  %>
  <h1> Sign in </h1>
  <form action="login" method="post">
     user name :<input type="text" name="username" value="${unamecookie}"><br>
     password ：<input type="password" name="pass"><br>
    <input type="submit" value=" Sign in ">
  </form>
  </body>
</html>

2.session Use

1. Login successful session Store value , Set the expiration time

package servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;

@WebServlet(urlPatterns = "/login")
public class loginServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // Answer the parameters 
        String username = req.getParameter("username");
        String pass = req.getParameter("pass");
        // Write logic ： Right or wrong 
        if ("admin".equals(username)&&"123456".equals(pass)){
            // Login successful 
            //session Store value 
            HttpSession session = req.getSession();
            session.setAttribute("username",username);
            session.setAttribute("psssword",pass);
            // Set up session Failure time 
            session.setMaxInactiveInterval(60*30);// The unit is seconds 
            // Redirect or forward ,session Data is not lost , But when redirecting ,requet The data will be lost 
            resp.sendRedirect("success.jsp");
        }else{
            // Login failed 
            //1. Create in the background cookie
            Cookie cookie = new Cookie("uname",username);
            //2. Back to the front end 
            resp.addCookie(cookie);
            resp.sendRedirect("index.jsp");
        }
    }
}

2. Show session

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>testsession.jsp</h1>
 Currently logged in user :${sessionScope.username}<br>
</body>
</html>

3. Exit empty session request

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>success.jsp</h1>
 Currently logged in user :${sessionScope.username}<br>
<a href="loginout"> sign out </a>
</body>
</html>

4.servlet The processing class handles the exit request

package servlet;

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 java.io.IOException;

@WebServlet(urlPatterns = "/loginout")
public class LoginOutServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.getSession().invalidate();// send session invalid 
        resp.sendRedirect("index.jsp");
    }
}

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