Java中Session的詳解

更新時(shí)間：2021年10月10日 15:36:29 作者：XiaoMaGuai

這篇文章主要介紹了了解java中的session的相關(guān)問題，什么是session，session怎么用等，具有一定參考價(jià)值，需要的朋友可以了解下。

1.什么是session：

服務(wù)器會(huì)給每一個(gè)用戶（瀏覽器）創(chuàng)建一個(gè)session對(duì)象

一個(gè)session獨(dú)占一個(gè)瀏覽器，只要瀏覽器不關(guān)閉，這個(gè)session就一直存在

session稱為會(huì)話控制，存儲(chǔ)用戶會(huì)話所需的屬性和配置信息，這樣，用戶在應(yīng)用程序的web頁面跳轉(zhuǎn)時(shí)，存儲(chǔ)在session對(duì)象中的用戶信息不會(huì)丟擲，而是在整個(gè)用戶會(huì)話中一直保持下去

2.session的經(jīng)典應(yīng)用場(chǎng)景：

一個(gè)用戶登陸后，訪問該網(wǎng)站的其他網(wǎng)頁時(shí)，一直處于登錄狀態(tài)

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(biāo)識(shí)

getServletContext()：代表整個(gè)web服務(wù)

getAttribute(String)：獲取session的節(jié)點(diǎn)，比如你在其中一個(gè)Servlet中通過setAttribute(String,Object)配置了相關(guān)的session信息，然后通過另一個(gè)Servlet獲取這個(gè)Servlet中的session信息，就要用到getAttribute(String)這個(gè)方法

setAttribute(String,Object)：設(shè)置session節(jié)點(diǎn)

removeAttribute(String)：一出一個(gè)session節(jié)點(diǎn)

isNew()：判斷一個(gè)session是否是一個(gè)新的session

invalidate()：注銷session的

4.舉例

例1：創(chuàng)建一個(gè)session并獲取到session的ID，判斷這個(gè)session是否是新的session

步驟1：新建一個(gè)maven項(xiàng)目，使用webapp模板

步驟2：在Java文件夾下創(chuàng)建一個(gè)com.xiaoma.servlet.SessionDemo01的類，編寫servlet類文件

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(guān)信息，包括id，是否是新的session等
         String sessionId = session.getId();
         if(session.isNew()) {
             resp.getWriter().write("創(chuàng)建Session成功，ID為：" + sessionId);
         }else{
             resp.getWriter().write("Session已經(jīng)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

<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(gè)servlet中讀取另一個(gè)servlet中的session信息

步驟1：在Java文件夾下創(chuàng)建一個(gè)com.xiaoma.servlet.SessionDemo01的類，編寫servlet類文件

  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(guān)信息，包括id，是否是新的session等
         String sessionId = session.getId();
         if(session.isNew()) {
             resp.getWriter().write("創(chuàng)建Session成功，ID為：" + sessionId);
         }else{
             resp.getWriter().write("Session已經(jīng)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(chuàng)建一個(gè)com.xiaoma.servlet.SessionDemo02的類，編寫另一個(gè)用來讀取的servlet類，通過SessionDemo02來讀取SessionDemo01中的session信息

 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

     <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(duì)象信息

步驟1：在Java文件夾下創(chuàng)建一個(gè)com.xiaoma.pojo.Person的類，編寫我們的實(shí)體類

 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(chuàng)建一個(gè)com.xiaoma.servlet.SessionDemo01的類，編寫servlet類文件

  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(guān)信息，包括id，是否是新的session等
         String sessionId = session.getId();
         if(session.isNew()) {
             resp.getWriter().write("創(chuàng)建Session成功，ID為：" + sessionId);
         }else{
             resp.getWriter().write("Session已經(jīng)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(chuàng)建一個(gè)com.xiaoma.servlet.SessionDemo02的類，編寫另一個(gè)servlet類文件，用來讀取SessionDemo01中的Session對(duì)象信息

 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(duì)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(dòng)過期

  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(dòng)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(shí)session自動(dòng)過期

     <!--設(shè)置session的存活時(shí)間-->
     <session-config>
         <!--以分鐘為單位-->
         <session-timeout>1</session-timeout>
     </session-config>