Session

Session

session:

*服务器会给每一个用户（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！保存用户的信息，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.

*session把用户的数据写到用户独占session中，服务器端保存。

*session对象由服务器创建；

使用场景

*保存一个登录用户的信息

*购物车信息

*在整个网站中经常会使用的数据，我们将他保存在session中。

使用session

package com.fan.servlet;

import pojo.Person;

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

public class SessionDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决乱码问题
        req.setCharacterEncoding("gbk");
        resp.setCharacterEncoding("gbk");
        resp.setContentType("text/html;charset=utf-8");

        //得到session
        HttpSession session = req.getSession();

        //给session中存东西
        session.setAttribute("name",new Person("阿帆",22));

        //获取session的ID
        String sessionId = session.getId();

        //判断是不是新创建的
        if (session.isNew()){
            resp.getWriter().write("session创建成功，ID:"+sessionId);
        }else{
            resp.getWriter().write("session已经在服务器中存在了，ID:"+sessionId);

            //session创建的时候做了什么事情
           // Cookie cookie = new Cookie("JSESSIONID",sessionId);
           // resp.addCookie(cookie);


        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}

package com.fan.servlet;

import pojo.Person;

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

public class SessionDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决乱码问题
        req.setCharacterEncoding("gbk");
        resp.setCharacterEncoding("gbk");
        resp.setContentType("text/html;charset=utf-8");

        //得到session
        HttpSession session = req.getSession();

        //给session中存东西
        Person person = (Person) session.getAttribute("name");
        System.out.println(person.toString());


    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}

package pojo;

public class Person {
    private String name;
    private int age;

    public Person() {

    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

<?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"
         metadata-complete="true">
    
    <servlet>
        <servlet-name>CookieDemo01</servlet-name>
        <servlet-class>com.fan.servlet.CookieDemo01</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>CookieDemo01</servlet-name>
        <url-pattern>/f</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>SessionDemo01</servlet-name>
        <servlet-class>com.fan.servlet.SessionDemo01</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>SessionDemo01</servlet-name>
        <url-pattern>/t</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>SessionDemo02</servlet-name>
        <servlet-class>com.fan.servlet.SessionDemo02</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>SessionDemo02</servlet-name>
        <url-pattern>/u</url-pattern>
    </servlet-mapping>
</web-app >

package com.fan.servlet;

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;

public class SessionDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        session.removeAttribute("name");
        session.invalidate();//注销session
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}

<!--session的默认失效时间，写在xml里面-->
    <session-config>
<!--十分钟后session自动失效-->
        <session-timeout>10</session-timeout>
    </session-config>