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HttpSessionActivationListener

实现了HttpSessionActivationListener接口的 JavaBean 对象可以感知自己被活化和钝化的事件

当绑定到 HttpSession 对象中的对象将要随 HttpSession 对象被钝化之前，web 服务器调用如下方法sessionWillPassivate(HttpSessionBindingEvent event) 方法 当绑定到 HttpSession 对象中的对象将要随 HttpSession 对象被活化之后，web 服务器调用该对象的 void sessionDidActive(HttpSessionBindingEvent event)方法

• 钝化状态：

  就是将Session内存中的对象持久化（序列化）到磁盘

• 活化状态：

  就是将磁盘上的对象再次恢复到session内存中

HttpSessionActivationListener API

配置HttpSessionActivationListener

可以通过配置文件指定：

• 多长时间不使用被钝化
• 钝化文件的位置

在META-INF下创建一个context.xml

示例：

创建User类，实现HttpSessionActivationListener和Serializable接口：

package pers.zhang.domain;import javax.servlet.http.HttpSessionActivationListener;import javax.servlet.http.HttpSessionEvent;import java.io.Serializable;/** * @author zhang * @date 2019/9/20 - 19:14 */public class User implements HttpSessionActivationListener, Serializable {
       private Integer userId;    private String userName;    public User(Integer id, String name){
           this.userId = id;        this.userName = name;    }    public Integer getUserId() {
           return userId;    }    public String getUserName() {
           return userName;    }    public void setUserId(Integer userId) {
           this.userId = userId;    }    public void setUserName(String userName) {
           this.userName = userName;    }    //钝化    @Override    public void sessionWillPassivate(HttpSessionEvent httpSessionEvent) {
           System.out.println("User被钝化...");    }    //活化    @Override    public void sessionDidActivate(HttpSessionEvent httpSessionEvent) {
           System.out.println("User活化...");    }}

将User存入Session：

package pers.zhang.servlet;import pers.zhang.domain.User;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.util.Date;/** * @author zhang * @date 2019/9/20 - 19:20 */public class SetUserServlet extends HttpServlet {
       protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
           //获得Session        HttpSession session = request.getSession();        //将User放到session中        User user = new User(1, "Tom");        session.setAttribute("user", user);        System.out.println("user被放到session中：" + new Date().toString());    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
           doPost(request, response);    }}

从session中取出User：

package pers.zhang.servlet;import pers.zhang.domain.User;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;/** * @author zhang * @date 2019/9/20 - 19:32 */public class GetUserServlet extends HttpServlet {
       protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
           //获得session        HttpSession session = request.getSession();        User user = (User) session.getAttribute("user");        System.out.println("user被活化：" + user.getUserId() + "," + user.getUserName());    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
           doPost(request, response);    }}

启动服务器，并访问SetUserServlet,控制台输出：

user被放到session中：Fri Sep 20 20:13:01 CST 2019

关闭服务器，控制台输出：

User被钝化...

再次启动服务器，访问GetUserServlet,控制台输出：

user被活化：1,Tom

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