20220716_JavaWeb_Cookie和Session的使用

PeterWarne

已于 2022-07-17 02:51:40 修改

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分类专栏： JavaWeb 文章标签： servlet java 开发语言

于 2022-07-17 02:42:55 首次发布

本文链接：https://blog.youkuaiyun.com/ClarkGable/article/details/125827631

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本文通过创建JavaWeb项目，演示了Cookie和Session的使用。从设置Cookie的存活时间到处理中文存储，再到Session的会话维持，详细解释了它们在实际应用中的工作流程。同时，探讨了Session的生命周期及其在服务器重启后的处理方式。

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IDEA新建一个不取名的empty项目，建好后新建一个名为Cookie_Demo的maven模块，本文结构图如下
请添加图片描述
pom.xml文件配置如下

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>Cookie_Demo</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.2</version>
            <scope>provided</scope>
        </dependency>

        <!--jstl tags-->
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
            </plugin>
        </plugins>
    </build>
</project>

文章目录

Cookie部分
建第一个servlet

package com.diy.web.cookie;

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

@WebServlet("/aServlet")
public class aServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //first attempt to transit cookies
        Cookie ck = new Cookie("username", "luo_xiang");

        /**
         * Cookie live time , by second here is 60*60*24*7 = 604800s, means one week
         * you can also put a 60*60*24*7 in (), but it will need cpu calculating once
         * for high performance, here prefer put 604800
         */
        ck.setMaxAge(604800);

        response.addCookie(ck);
    }

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

建第二个

package com.diy.web.cookie;

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

@WebServlet("/bServlet")
public class bServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // receive cookie
        Cookie[] cks = request.getCookies();

        for (Cookie ck : cks) {
            String name = ck.getName();
            if ("username".equals(name)){
                String value = ck.getValue();
                System.out.println(name + ":" + value);
                break;
            }
        }
    }

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

运行tomcat，浏览器访问项目路径加第一个servlet的访问路径，访问之前打开开发者页面
看到响应头已经有set-cookie了

访问第二个servlet的路径，就看到IDEA的控制台输出cookie里存储的数据了

ck.setMaxAge(604800);

该语句设置cookie的存活时间，正数是寿命，0是删除该cookie，浏览器默认是负数，即当浏览器关闭，发送的cookie被删除
请添加图片描述
这张图中看到服务器响应的cookie，过期时间，和浏览器请求时携带的cookie

cookie中存储中文时，需要转码，否则发给浏览器，浏览器再携带该cookie访问服务端资源时，服务端得到的将是乱码
第三个servlet

package com.diy.web.cookie;

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;
import java.net.URLEncoder;

@WebServlet("/cServlet")
public class cServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /**
         * deposit 中文 in Cookie, you need encoding by yourself
         */

        String name = "羅翔";
        name = URLEncoder.encode(name,"utf-8");
        System.out.println("deposit nameCookie by C: "+ name);

        Cookie ck = new Cookie("username", name);

        ck.setMaxAge(604800);

        response.addCookie(ck);
    }

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

第四个servlet

package com.diy.web.cookie;

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;
import java.net.URLDecoder;
import java.net.URLEncoder;

@WebServlet("/dServlet")
public class dServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // receive cookie
        Cookie[] cks = request.getCookies();

        for (Cookie ck : cks) {
            String name = ck.getName();
            if ("username".equals(name)){
                String value = ck.getValue();

                value = URLDecoder.decode(value,"utf-8");

                System.out.println("receive nameCookie by D: " + value);

                break;
            }
        }
    }

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

重启tomcat，浏览器访问第三个servlet会得到cookie，然后浏览器再访问第四个servlet携带cookie
请添加图片描述
含有中文的cookie发送时为16进制码

请添加图片描述

手动用utf-8编码发送给浏览器的cookie，再从浏览器那里获取后，手动utf-8解码，就得到原来存入的正确的汉字信息

文章目录

Session部分
建两个servlet，一

package com.diy.web.session;

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

@WebServlet("/demo1")
public class SessionServletDemo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //get session object
        HttpSession sess = request.getSession();

        //deposit data, the value type is object, so any type is ok
        sess.setAttribute("accountId", "jason_bourne");

        System.out.println("Print from demo1: "+sess);
    }

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

二

package com.diy.web.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;

@WebServlet("/demo2")
public class SessionServletDemo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //get session object
        HttpSession sess = request.getSession();

        /**
         * this statement will kill session itself
         * sess.invalidate();
         * can use at user logout timing
         */

        System.out.println("Print from demo2: "+sess);

        //receive data
        Object accountId = sess.getAttribute("accountId");

        System.out.println(accountId);
    }

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

访问demo1会看到服务器响应了一个JSESSIONID的cookie，所以说服务器维持会话其实就是基于它发送给浏览器的cookie
请添加图片描述
访问demo2会看到这个JSESSIONID已经携带进请求的cookie里了

并且demo1在session里存入的数据，当demo2被访问之后，也按照代码被输出了

给demo1和demo2加上直接输出session对象地址的sout可以看到地址一样

在浏览器的设置中找localhost发来的cookie也可以看到有相应的JSESSIONID
请添加图片描述

文章目录

session的钝化机制
如果服务器正常关闭，session不会丢失，因为正常关闭会在服务器硬盘上存储一个session的ser文件

切换Terminal页面，在本项目路劲下输入mvn tomcat7:run启动项目
浏览器访问demo1
Ctrl+C正常关闭tomcat
这时在项目的target目录下的如下地址请添加图片描述
会看见ser文件，服务器重启后会立刻自动删除

mvn tomcat7:run启动tomcat
浏览器访问demo2
输出内容正确输出
请添加图片描述

文章目录

session的过期时间
可以在web.xml文件中添加配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <!--以下标签可配置session的有效时间，tomcat的默认值是30，就是30分钟-->
<!--    <session-config>
        <session-timeout>90</session-timeout>
    </session-config>-->
</web-app>

关闭session，可在servlet中写上下面注释中的代码

        /**
         * this statement will kill session itself
         * sess.invalidate();
         * can use at user logout timing
         */

完