java web会话监听并使用spring注入

      在java web应用中，当你想在建立会话或移除会话时，让系统做某些事情，比如说，统计在线用户，每当有用户登录时，或退出时，那么可以用下面这个监听器来监听。

import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

public class OnlineCountListener implements HttpSessionAttributeListener ,HttpSessionListener,ServletContextListener{
	/**
	 * 定义监听的session属性名.
	 */
	public final static String LISTENER_NAME = "user_name";

	/**
	 * 定义存储客户登录session的集合.
	 */
	private static List sessions = new ArrayList();
	
	private static int userSum=0;

	/**
	 * session加入某值时此方法会被调用.
	 * 
	 * @param HttpSessionBindingEvent
	 *            session事件
	 */
	public void attributeAdded(HttpSessionBindingEvent sbe) {
		if (LISTENER_NAME.equals(sbe.getName())) {
			sessions.add(sbe.getValue());
		}
	}

	/**
	 * session失效时的监听方法.
	 * 
	 * @param HttpSessionBindingEvent
	 *            session事件
	 */
	public void attributeRemoved(HttpSessionBindingEvent sbe) {
		if (LISTENER_NAME.equals(sbe.getName())) {
			sessions.remove(sbe.getValue());
		}
	
	}

	/**
	 * session覆盖时的监听方法.
	 * 
	 * @param HttpSessionBindingEvent
	 *            session事件
	 */
	public void attributeReplaced(HttpSessionBindingEvent sbe) {
		if (LISTENER_NAME.equals(sbe.getName())) {
			sessions.remove(sbe.getValue());
			sessions.add(sbe.getValue());
		}
	}
	public void sessionCreated(HttpSessionEvent arg) {
		userSum++;
	}

	public void sessionDestroyed(HttpSessionEvent arg) {
		userSum--;
	}

	/**
	 * 返回客户登录session的集合.
	 * 
	 * @return
	 */
	public static List getSessions() {
		return sessions;
	}
	
	public static int getMemberSum() {
		return sessions.size();
	}
	
	public static int getSum() {
		return userSum;
	}

	public static Boolean isExistInSessions(String username) {
		String user_name;
		for (Integer i = 0; i < sessions.size(); i++) {
			user_name = (String) sessions.get(i);
			if (user_name.equals(username)) {
				return true;
			} else {
				continue;
			}
		}
		return false;
	}

	//此方法在初始化监听器的时候会调用，用于spring注入
	public void contextInitialized(ServletContextEvent sce) {  
        WebApplicationContext applicationContext =    WebApplicationContextUtils.getWebApplicationContext(sce.getServletContext());  
        this.xxxService=(XxxService)applicationContext.getBean("xxxService"); 
      
    }  
    public void contextDestroyed(ServletContextEvent sce) {  
          
    }  
	
    private XxxService xxxService;//这里是你希望注入的服务类

    public XxxService  getXxxService(){
      return this.xxxService;
    }

   public void setxxxService(XxxService xxxService){
   this.xxxService=xxxService;
   }
}

 在web.xml中加入以下配置代码，注意必须在spring容器配置之后。

  <listener>
       <listener-class>  
				com.xxx.xxx.xxx.OnlineCountListener
      </listener-class>
  </listener>

 然后在spring配置

 <bean id="xxxService">xxx.xxx.xxx.xxxService</bean>