Web项目实现ServletContextListener接口

川长思鸟来 2022-05-18 09:30 145阅读 0赞

## 源码 ##

package javax.servlet;
    
    import java.util.EventListener;
    
    /** * Implementations of this interface receive notifications * about changes to the servlet context of the web * application they are part of. To receive notification events, * the implementation class must be configured in the * deployment descriptor for the web application. * @see ServletContextEvent * @since v 2.3 */
    
    public interface ServletContextListener extends EventListener { 
    
        /** ** Notification that the web application initialization process * is starting. All ServletContextListeners are notified of * context initialization before any filter or servlet in the * web application is initialized. * @param sce Information about the ServletContext that was * initialized * 当Servlet 容器启动Web 应用时调用该方法。 */
        public void contextInitialized(ServletContextEvent sce);
    
        /** ** Notification that the servlet context is about to be shut * down. All servlets and filters have been destroy()ed * before any ServletContextListeners are notified of context * destruction. * @param sce Information about the ServletContext that was * destroyed * 当Servlet 容器终止Web 应用时调用该方法。 */
        public void contextDestroyed(ServletContextEvent sce);
    }

## 介绍 ##

> ServletContextListener本质上就是一个监听器，监听 Web 应用的生命周期

在 Servlet API 中有一个 ServletContextListener 接口，它能够监听 ServletContext 对象的生命周期，实际上就是监听 Web 应用的生命周期。

当Servlet 容器启动或终止Web 应用时，会触发ServletContextEvent 事件，该事件由ServletContextListener 来处理。在 ServletContextListener 接口中定义了处理ServletContextEvent 事件的两个方法。

## 项目代码实现 ##

### 定义一个监听器 ###

public class OperationReplyListener implements ServletContextListener { 
    
        private static final Log logger = LogFactory.getLog(OperationReplyListener.class);
        final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);  
    
        public void contextDestroyed(ServletContextEvent sce) {
    
        }
    
        public void contextInitialized(ServletContextEvent sce) {
            logger.info("定时器启动...");
            OperationReplyTask operationReplyTask = new OperationReplyTask();
            scheduler.scheduleAtFixedRate(operationReplyTask, 2, 5, TimeUnit.SECONDS);
        }
    }

### web.xml中配置监听器 ###

<listener>
        <listener-class>com.sto.rookie.timer.OperationReplyListener</listener-class>
    </listener>