Listener--HttpSessionActivationListener(钝化、活化)API、配置和使用详解

快来打我* 2021-08-13 14:09 294阅读 0赞

#### 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![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70] ####

#### 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**

<?xml version="1.0" encoding="UTF-8"?>
    <Context>
        
        <Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwqp="1" >
            
            <Store className="org.apache.catalina.session.FileStore" directory="file" />
        </Manager>
    </Context>

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

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70]: /images/20210813/1d0dceb43af146568137f78691580fdc.png