SpringBoot中Session监听器的使用

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当需要统计应用的试试在线人数的时候，统计成功登录后创建的session的数量是最为准确的数据。SpringBoot通过SessionListener可以很方便的监听session的生命周期。在SpringBoot中监听session的步骤如下：
1、创建session监听器.

package com.sds.listenner;

import java.util.HashSet;

import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

@WebListener
public class SessionListener implements HttpSessionListener, HttpSessionAttributeListener {

    public Logger logger = new Logger();

    @Override
    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
        logger.info("--attributeAdded--");
        @SuppressWarnings("unused")
        HttpSession session = httpSessionBindingEvent.getSession();
        logger.info("key----:" + httpSessionBindingEvent.getName());
        logger.info("value---:" + httpSessionBindingEvent.getValue());

    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {
        logger.info("--attributeRemoved--");
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {
        logger.info("--attributeReplaced--");
    }

    @Override
    public void sessionCreated(HttpSessionEvent event) {
        logger.info("---sessionCreated----");
        HttpSession session = event.getSession();
        ServletContext application = session.getServletContext();
        // 在application范围由一个HashSet集保存所有的session
        @SuppressWarnings("unchecked")
        HashSet<HttpSession> sessions = (HashSet<HttpSession>) application.getAttribute("sessions");
        if (sessions == null) {
            sessions = new HashSet<HttpSession>();
            application.setAttribute("sessions", sessions);
        }
        // 新创建的session均添加到HashSet集中
        sessions.add(session);
        // 可以在别处从application范围中取出sessions集合
        // 然后使用sessions.size()获取当前活动的session数，即为“在线人数”

        //添加新建的session到MySessionContext中;
        MySessionContext.AddSession(event.getSession());
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent event) throws ClassCastException {
        logger.info("---sessionDestroyed----");
        HttpSession session = event.getSession();
        logger.info("deletedSessionId: " + session.getId());
        System.out.println(session.getCreationTime());
        System.out.println(session.getLastAccessedTime());
        ServletContext application = session.getServletContext();
        HashSet<?> sessions = (HashSet<?>) application.getAttribute("sessions");
        // 销毁的session均从HashSet集中移除
        sessions.remove(session);

        //添加新建的session到MySessionContext中;
        MySessionContext.DelSession(session);
    }

}

2、创建session处理工具类，里面需要一个静态的HashMap存储应用中登录后创建的有效的session.

package com.sds.listenner;

import java.util.HashMap;

import javax.servlet.http.HttpSession;

public class MySessionContext {
    private static HashMap<String, HttpSession> mymap = new HashMap<String, HttpSession>();
        public static synchronized void AddSession(HttpSession session) {
                if (session != null) {
                        mymap.put(session.getId(), session);
                     }
             }
         public static synchronized void DelSession(HttpSession session) {
                 if (session != null) {
                         mymap.remove(session.getId());
                     }
             }
         public static synchronized HttpSession getSession(String session_id) {
                if (session_id == null)
                     return null;
                 return mymap.get(session_id);
             }
}

Logger.java

package com.sds.listenner;

public class Logger {
    public void info(String info) {
        System.out.println(info);
    }
}

3、添加SessionListener到系统配置中:

package com.sds.cfg;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
@Configuration
public class SessionConfiguration extends WebMvcConfigurerAdapter{
    //注册session监听器;
    @Bean
    public ServletListenerRegistrationBean<SessionListener> servletListenerRegistrationBean() {
        ServletListenerRegistrationBean<SessionListener> slrBean = new ServletListenerRegistrationBean<SessionListener>();
        slrBean.setListener(new SessionListener());
        return slrBean;
    }

}

原理：通过SessionListener监听session的创建和销毁，并在对应的session生命周期中从静态的HashMap【自定义的session容器】中添加或者删除对应的session，从而实现session的动态管理，提供准确的统计数据。

注意：在本例中提供了根据sessionId获取session的方法。