Servlet的Session技术

小鱼儿 2021-07-24 11:19 595阅读 0赞

# 什么是Session #

*  服务器给每个用户（浏览器）创建一个Session对象。
 *  一个Session独占一个浏览器，只要浏览器没有关闭，这个Session就存在。
 *  用户登录之后，整个网站它都可以访问，Session可以保存用户的信息，可以保存购物车的信息。

# Session和cookie的区别 #

*  cookie是把用户的数据写给用户的浏览器，浏览器保存（可以保存多个）。
 *  Seesion把用户的数据写到用户独占的Session中，服务端保存（保存重要的信息，减少服务器资源的浪费）。
 *  Session由服务器创建。

# 使用场景 #

*  保存用户登录信息
 *  保存购物车信息
 *  在整个网站经常要用的数据，保存到Session中。

# 实战 #

1 创建session

package com.cakin.session;
    
    
    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;
    
    
    /**
    * @className: SessionDemo01
    * @description: 创建session
    * @date: 2020/6/9
    * @author: cakin
    */
    public class SessionDemo01 extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            // 解决乱码问题
            req.setCharacterEncoding("utf-8");
            resp.setCharacterEncoding("utf-8");
            // 获得session
            HttpSession session = req.getSession();
            Person person = new Person("xiaowang", "20");
            // 创建session
            session.setAttribute("person", person);
            // 浏览器输出
            PrintWriter out = resp.getWriter();
            if (session.isNew()) {
                out.write("session is new");
            } else {
                // 打印session
                out.write("session is" + session.getId());
            }
        }
    
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req, resp);
        }
    }

2 获取session

package com.cakin.session;
    
    
    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;
    
    
    /**
    * @className: SessionDemo02
    * @description: 获取session
    * @date: 2020/6/9
    * @author: cakin
    */
    public class SessionDemo02 extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            // 获取session
            HttpSession session = req.getSession();
    
    
            Person person = (Person) session.getAttribute("person");
    
    
            PrintWriter out = resp.getWriter();
            // 获取session
            out.write("persion " + person.toString());
    
    
        }
    
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req, resp);
        }
    }

3 删除session

package com.cakin.session;
    
    
    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;
    
    
    /**
    * @className: SessionDemo03
    * @description: 删除session
    * @date: 2020/6/9
    * @author: cakin
    */
    public class SessionDemo03 extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
            HttpSession session = req.getSession();
            // 删除session
            session.removeAttribute("person");
            // session失效
            session.invalidate();
        }
    
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req, resp);
        }
    }

4 Person

package com.cakin.session;
    
    
    /**
    * @className: Person
    * @description: Person实体类
    * @date: 2020/6/9
    * @author: cakin
    */
    public class Person {
        private String name;
        private String age;
    
    
        public Person(String name, String age) {
            this.name = name;
            this.age = age;
        }
    
    
        public String getName() {
            return name;
        }
    
    
        public void setName(String name) {
            this.name = name;
        }
    
    
        public String getAge() {
            return age;
        }
    
    
        public void setAge(String age) {
            this.age = age;
        }
    
    
        public Person() {
        }
    
    
        @Override
        public String toString() {
            return "Person{" +
                    "name='" + name + '\'' +
                    ", age='" + age + '\'' +
                    '}';
        }
    }

5 配置

<?xml version="1.0" encoding="ISO-8859-1"?>
    
    
    <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_3_1.xsd"
             version="3.1"
             metadata-complete="true">
    
      <servlet>
        <servlet-name>SessionDemo01</servlet-name>
        <servlet-class>com.cakin.session.SessionDemo01</servlet-class>
      </servlet>
      <servlet-mapping>
        <servlet-name>SessionDemo01</servlet-name>
        <url-pattern>/SessionDemo01</url-pattern>
      </servlet-mapping>
    
    
      <servlet>
        <servlet-name>SessionDemo02</servlet-name>
        <servlet-class>com.cakin.session.SessionDemo02</servlet-class>
      </servlet>
      <servlet-mapping>
        <servlet-name>SessionDemo02</servlet-name>
        <url-pattern>/SessionDemo02</url-pattern>
      </servlet-mapping>
    
    
      <servlet>
        <servlet-name>SessionDemo03</servlet-name>
        <servlet-class>com.cakin.session.SessionDemo03</servlet-class>
      </servlet>
      <servlet-mapping>
        <servlet-name>SessionDemo03</servlet-name>
        <url-pattern>/SessionDemo03</url-pattern>
      </servlet-mapping>
    
    
      <session-config>
        
        <session-timeout>15</session-timeout>
      </session-config>
    </web-app>