梦入琼楼寒有月，行过石树冻无烟

JSP Servlet 会话管理

2022-04-21

会话跟踪在通常是用于维持用户数据和状态的方法，通常分为Cookie和session两项常用技术。在Servlet也被称之为Servlet会话管理，也可以称之为“会话追踪”都是没有问题的。当用户通过浏览器来访问和进行交互请求的时候，我们需要使用Cookie和session两项中的任意一项来维护状态，每次用户向服务器请求时，服务器就将会该请求视为新的请求。所谓为了避免这种问题，需要区别进行对待，在这种情况中会话跟踪技术慢慢的发展和壮大。

Cookie即“小饼干”，是为了Web站点进行辨别用户从而实现免密登入来进行访问，和Session的区别之处在于Cookie将数据存储于客户端中，而Session存储与服务器之中。Cookie可以包含用户信息、小文本文件等信息，通过Cookie技术，可以让用户何时访问Web服务器，Web都可以通过访问或获取存储于用户本地之中的Cookie进行利用。

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Cookie vistedCountC = new Cookie ("name", "null");

通过上方的Cookie够走可以看出，name可指定Cookie的属性名，第二个参数null可以用于指定值。创建完Cookie可以使用addCookie()添加到响应对象之中那个，从而实现存储于用户本地计算机上。如果想实现访问或获取存储于用户计算机之中的Cookie的数据可以通过getCookies()来进而获取。

在Cookie中有一定的存活时间，不可能在客户端中永久保存，这样会给安全性带来问题，在默认的情况之下Cookie在用户关闭之时将会自动会被销毁，如果想自行进行定义可以使用setMaxAge(int time)方法来设置Cookie的存货时间。

ID DA FA
AddCookie() 将Cookie添加到响应对象中 即存储于用户计算机中
getCookies() 来获取用户计算机之中的Ckkoie数据
setMaxAge(int time) 设置Cookie存活时间 如为整数则以秒进行计算，为负数则表示为临时Cookie，但为0则表明通知浏览器删除相应Cookie数据

访问次数

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package Cookie;

import java.util.Date;
import java.text.SimpleDateFormat;
import java.io.IOException;
import java.io.PrintWriter;
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;

/**
 * Servlet implementation class TimeCookie
 */
@WebServlet("/TimeCookie")
public class TimeCookie extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public TimeCookie() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=UTF-8");

		// Time
		PrintWriter printWriter = response.getWriter();
		SimpleDateFormat simpledateformat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		String nowTime = simpledateformat.format(new Date());
		// 访问时间
		String lastVistTime = "";
		// 访问次数
		int vistedCount = 0;
		// 获取Cookie
		Cookie[] myCookies = request.getCookies();
		if (myCookies != null) {
			for (Cookie cookie:myCookies) {
				// 是否为最近访问的Cookies
				if ("lastVist".equals(cookie.getName())) {
					lastVistTime = cookie.getValue();
				}
				if ("vistedCount".equals(cookie.getName())) {
					vistedCount = Integer.valueOf(cookie.getValue());
				}
			}
		}
		if (!"".equals(lastVistTime)) {
			printWriter.println("上次访问时间" + lastVistTime);
		}
		// 访问次数
		printWriter.println("访问次数" + (vistedCount +1));
		// 创建 Cookie
		Cookie lastVistTimeC = new Cookie("lastVist",nowTime);
		// Cookie 生存时间
		lastVistTimeC.setMaxAge(365*24*60*60);
		// 访问时创建同名cookie
		Cookie vistedCpimtC = new Cookie("vistedCount", (vistedCount +1) + "");
		// Cookie Timesize
		vistedCpimtC.setMaxAge(365*24*60*60);
		
		// 将Cookie添加到响应客户端中
		response.addCookie(lastVistTimeC);
		response.addCookie(vistedCpimtC);
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

登录演示

ID DA FA
Lagin 登录界面 JSP
LoginServlet 登入验证 Servlet
LogoutServlet Cookie注销 Servlet
ProfileServlet 获取Cookie Servlet

Lagin.jsp

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<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="LoginServlet" method="post">
		user:<input type="text" name="name"></br>
		Pass:<input type="password" name="password"><br>
		<input type="submit" value="login">
	</form>
</body>
</html>

LoginServlet.java

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package Cookie;

import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class LoginServlet
 */
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=UTF-8");
		PrintWriter out = response.getWriter();
		
		// user and password
		String name = request.getParameter("name");
		String password = request.getParameter("password");
		
		// pass or user 
		if (password.equals("admin")) {
			out.println("Yes!");
			out.println("<br>User" + name);
			
			// Cookie
			Cookie cookie = new Cookie("name", name);
			response.addCookie(cookie);		// 添加到响应头
		} else {
			out.println("No!");
			request.getRequestDispatcher("login.jsp").include(request, response);
		}
		out.close();
	}

}

LogoutServlet.java

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package Cookie;

import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class LoginServlet
 */
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=UTF-8");
		PrintWriter out = response.getWriter();
		
		// user and password
		String name = request.getParameter("name");
		String password = request.getParameter("password");
		
		// pass or user 
		if (password.equals("admin")) {
			out.println("Yes!");
			out.println("<br>User" + name);
			
			// Cookie
			Cookie cookie = new Cookie("name", name);
			response.addCookie(cookie);		// 添加到响应头
		} else {
			out.println("No!");
			request.getRequestDispatcher("login.jsp").include(request, response);
		}
		out.close();
	}

}

ProfileServlet.java

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package Cookie;

import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class LoginServlet
 */
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=UTF-8");
		PrintWriter out = response.getWriter();
		
		// user and password
		String name = request.getParameter("name");
		String password = request.getParameter("password");
		
		// pass or user 
		if (password.equals("admin")) {
			out.println("Yes!");
			out.println("<br>User" + name);
			
			// Cookie
			Cookie cookie = new Cookie("name", name);
			response.addCookie(cookie);		// 添加到响应头
		} else {
			out.println("No!");
			request.getRequestDispatcher("login.jsp").include(request, response);
		}
		out.close();
	}

}

session

session即HttpSession对象实现会话跟踪技术，而Session和Cookie的区别就是当用户第一次访问服务器的时候将会创建一个session对象，之后将会为其分配一个唯一的会话标识（sessionId）之后将会以"JSESSIONID"作为属性名保存在客户端cookie中

Session 对象

ID DA FA
getSession() 返回与此请求关联的当前会话 如果没有则创建一个
getSession (boolean create) 返回与此请求关联的当前HttpSession 或者如果当前没有create为true，则创建一个对象
getAttribute() 获取指定属性

Session 接口

ID DA FA
getRequestedSessionId() 返回包含session唯一标识符的字符串
getCreation Time() 返回创建此会话的时间 以格林尼治标准时间1970年1月1日午夜以来的毫秒数来作为单位
getLastAccessedTime() 返回客户端最后一次发送与此会话相关的请求时间 以格林尼治标准时间1970年1月1日午夜以来的毫秒数来作为单位
invalidate() 使得此会话无效，之后取消绑定到该会话中的任何对象

Session 获取用户名

通过setSession() 和getAttribute()对象，实现了Servlet通过session来获取jsp中用户填写的数据并使用了url重写：

login.jsp

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<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="finstServlet">
	Username<input type="text" name="nameuser">
	<input type="submit" value="up">
</form>
</body>
</html>
````
#### session.java
```java
package session;

import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class secondServlet
 */
@WebServlet("/secondServlet")
public class session extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public session() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		HttpSession session = request.getSession(false);
		String uaname = (String)session.getAttribute("uname");
		out.println("Hello:" + uaname);
		
		out.close();
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

finstServlet.java

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package session;


import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class finstServlet
 */
@WebServlet("/finstServlet")
public class attribute extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public attribute() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		String name = request.getParameter("nameuser");
		out.println("用户: " + name);
		
		HttpSession session = request.getSession();
		session.setAttribute("uname", name);
		
		out.println("| <a href='secondServlet'>secondServlet</a>");
		out.close();
	} 

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

secondServlet.java

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package session;

import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class secondServlet
 */
@WebServlet("/secondServlet")
public class secondservlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public secondservlet() {
		super();
		// TODO Auto-generated constructor stub
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();

		HttpSession session = request.getSession(false);
		String uaname = (String) session.getAttribute("uname");
		out.println("Hello:" + uaname);

		out.close();
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

获取session id

从Session获取用户名的基础上，我们在finstServlet中加入（getRequestedSessionId）即可获取到session ID：

finstServlet.java

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package session;


import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class finstServlet
 */
@WebServlet("/finstServlet")
public class firstservlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public firstservlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		String name = request.getParameter("nameuser");
		out.println("用户: " + name);
		
		HttpSession session = request.getSession();
		session.setAttribute("uname", name);
		
		out.println(request.getRequestedSessionId());
		
		out.println("| <a href='secondServlet'>secondServlet</a>");
		out.close();
	} 

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

URL重写

使用url重写的优势在于无论浏览器是否禁用cookie或session，传输都将有效，也不需要在每个页面上提交额外的网关，关于重写url和不重写url的区别可以是：

ID DA
http://localhost:8080/Testsp/secondServlet?uname=Adminsitrator url重写
http://localhost:8080/Testsp/secondServlet 正常url

重写 secondServlet.java url

finstServlet.java

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package session;


import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class finstServlet
 */
@WebServlet("/finstServlet")
public class firstservlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public firstservlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		String name = request.getParameter("nameuser");
		out.println("用户: " + name);
		
		HttpSession session = request.getSession();
		session.setAttribute("uname", name);
		
		
		out.println("| <a href='secondServlet?uname=" + name + "'>secondServlet</a>");
		out.close();
	} 

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

表单域隐藏

表单域和上述URL重写区别在于URL重写会将原先 http://localhost:8080/Testsp/secondServlet的链接改为http://localhost:8080/Testsp/secondServlet?uname=Adminsitrator，而隐藏表单域则会将URL重写后的链接写为“http://localhost:8080/Testsp/secondServlet”。表单域的有点则是不管Cookie是否禁用，都合URL重写一样，可以正常使用。

ID DA
URL 重写 http://localhost:8080/Testsp/secondServlet?uname=Adminsitrator
表单域隐藏 http://localhost:8080/Testsp/secondServlet

login.jsp

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<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="finstServlet" method="post">
	Username:<input type="text" name="nameuser">
	<input type="submit" value="up">
</form>
</body>
</html>

finstServlet.java

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package session;


import java.io.IOException;
import java.io.PrintWriter;

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;

/**
 * Servlet implementation class finstServlet
 */
@WebServlet("/finstServlet")
public class firstservlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public firstservlet() {
        super();
        // TODO Auto-generated constructor stub
    }
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		String name = request.getParameter("nameuser");
		out.print("User: " + name);	
	/*
		out.print("<form action='secondServlet'>");
		out.print("<input type='hidden' name='namer' value='" + name + "'>");
		out.print("<input type='submit' value='up'>");
		out.print("</form>");
		*/
		out.close();
	} 

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}
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