1.什么是session：
服務器會給每一個用戶（瀏覽器）創建一個session對象
一個session獨占一個瀏覽器，只要瀏覽器不關閉，這個session就一直存在
session稱為會話控制，存儲用戶會話所需的屬性和配置信息，這樣，用戶在應用程序的web頁面跳轉時，存儲在session對象中的用戶信息不會丟擲，而是在整個用戶會話中一直保持下去
2.session的經典應用場景：
一個用戶登陸后，訪問該網站的其他網頁時，一直處于登錄狀態
保存購物車信息等等
3.session中常用的方法
getId()：獲取session的唯一標識
getServletContext()：代表整個web服務
getAttribute(String)：獲取session的節點，比如你在其中一個Servlet中通過setAttribute(String,Object)配置了相關的session信息，然后通過另一個Servlet獲取這個Servlet中的session信息，就要用到getAttribute(String)這個方法
setAttribute(String,Object)：設置session節點
removeAttribute(String)：一出一個session節點
isNew()：判斷一個session是否是一個新的session
invalidate()：注銷session的
4.舉例
例1：創建一個session并獲取到session的ID，判斷這個session是否是新的session
步驟1：新建一個maven項目，使用webapp模板
步驟2：在Java文件夾下創建一個com.xiaoma.servlet.SessionDemo01的類，編寫servlet類文件
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package com.xiaoma.servlet;import com.xiaoma.pojo.Person;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 SessionDemo01 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //解決中文亂碼 resp.setHeader("content-type","text/html;charset=UTF-8"); //得到session HttpSession session = req.getSession(); //通過setAttribute方法向Session中存放信息 session.setAttribute("name","小馬"); //獲取session相關信息，包括id，是否是新的session等 String sessionId = session.getId(); if(session.isNew()) { resp.getWriter().write("創建Session成功，ID為：" + sessionId); }else{ resp.getWriter().write("Session已經存在了，ID為：" + sessionId); } } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } } |
步驟3：配置XML文件
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<servlet> <servlet-name>SessionDemo01</servlet-name> <servlet-class>com.xiaoma.servlet.SessionDemo01</servlet-class> </servlet> <servlet-mapping> <servlet-name>SessionDemo01</servlet-name> <url-pattern>/s1</url-pattern> </servlet-mapping> |
例2：從一個servlet中讀取另一個servlet中的session信息
步驟1：在Java文件夾下創建一個com.xiaoma.servlet.SessionDemo01的類，編寫servlet類文件
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package com.xiaoma.servlet; import com.xiaoma.pojo.Person; 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 SessionDemo01 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //解決中文亂碼 resp.setHeader("content-type","text/html;charset=UTF-8"); //得到session HttpSession session = req.getSession(); //通過setAttribute方法向Session中存放信息 session.setAttribute("name","小馬"); //獲取session相關信息，包括id，是否是新的session等 String sessionId = session.getId(); if(session.isNew()) { resp.getWriter().write("創建Session成功，ID為：" + sessionId); }else{ resp.getWriter().write("Session已經存在了，ID為：" + sessionId); } } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); }} |
步驟2：在Java文件夾下創建一個com.xiaoma.servlet.SessionDemo02的類，編寫另一個用來讀取的servlet類，通過SessionDemo02來讀取SessionDemo01中的session信息
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package com.xiaoma.servlet; import com.xiaoma.pojo.Person; 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 SessionDemo02 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //解決中文亂碼 resp.setHeader("content-type","text/html;charset=UTF-8"); //得到session HttpSession session = req.getSession(); String name=(String) session.getAttribute("name"); resp.getWriter().write(name); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doPost(req, resp); }} |
步驟3：配置xml文件
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<servlet> <servlet-name>SessionDemo02</servlet-name> <servlet-class>com.xiaoma.servlet.SessionDemo02</servlet-class></servlet><servlet-mapping> <servlet-name>SessionDemo02</servlet-name> <url-pattern>/s2</url-pattern></servlet-mapping> |
例3：session中還可以存放對象信息
步驟1：在Java文件夾下創建一個com.xiaoma.pojo.Person的類，編寫我們的實體類
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package com.xiaoma.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 + '}'; }} |
步驟2：在Java文件夾下創建一個com.xiaoma.servlet.SessionDemo01的類，編寫servlet類文件
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package com.xiaoma.servlet; import com.xiaoma.pojo.Person; 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 SessionDemo01 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //解決中文亂碼 resp.setHeader("content-type","text/html;charset=UTF-8"); //得到session HttpSession session = req.getSession(); //通過setAttribute方法向Session中存放信息 session.setAttribute("name",new Person("小馬",18)); //獲取session相關信息，包括id，是否是新的session等 String sessionId = session.getId(); if(session.isNew()) { resp.getWriter().write("創建Session成功，ID為：" + sessionId); }else{ resp.getWriter().write("Session已經存在了，ID為：" + sessionId); } } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); }} |
步驟3：在Java文件夾下創建一個com.xiaoma.servlet.SessionDemo02的類，編寫另一個servlet類文件，用來讀取SessionDemo01中的Session對象信息
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package com.xiaoma.servlet; import com.xiaoma.pojo.Person; 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 SessionDemo02 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //獲取session中的Person對象 //解決中文亂碼 resp.setHeader("content-type","text/html;charset=UTF-8"); //得到session HttpSession session = req.getSession(); Person person=(Person) session.getAttribute("name"); resp.getWriter().write(person.toString()); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doPost(req, resp); } } |
步驟4：編寫xml文件，與上同理
例4：注銷session（注銷session有兩種方式，一種是通過removeAttribute(String)方法，另一種是通過xml配置文件）
第一種，通過removeAttribute(String)方法，這種方式是使session手動過期
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package com.xiaoma.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 { //得到session HttpSession session = req.getSession(); //手動注銷session session.removeAttribute("name"); session.invalidate(); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doPost(req, resp); }} |
第二種，通過xml文件的方法，這種方式是時session自動過期
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<!--設置session的存活時間--><session-config> <!--以分鐘為單位--> <session-timeout>1</session-timeout></session-config> |
5.session與cookie的區別
·（1）cookie是吧用戶的數據寫給瀏覽器，瀏覽器保存(可以保存多個)
·（2）session是把用戶的數據寫給用戶獨占的session中，服務器保存（保存重要信息，避免浪費服務器資源）
·（3）session是由服務器創建的
原文鏈接：https://www.cnblogs.com/XiaoMaGuai/p/15374013.html
