1.首先来看一看源码 该类的源码
public interface ServletContextListener extends EventListener { / * Receives notification that the web application initialization * process is starting. * * All ServletContextListeners are notified of context * initialization before any filters or servlets in the web * application are initialized. * * @param sce the ServletContextEvent containing the ServletContext * that is being initialized */ public void contextInitialized(ServletContextEvent sce); / * Receives notification that the ServletContext is about to be * shut down. * *
All servlets and filters will have been destroyed before any * ServletContextListeners are notified of context * destruction. * * @param sce the ServletContextEvent containing the ServletContext * that is being destroyed */ public void contextDestroyed(ServletContextEvent sce); }
此接口中提供了两个方法，用于监听ServletContext 的创建和销毁，也就是监听ServletContext 的生命周期，可以说成是监听Web 应用的生命周期，当web应用启动后，就会触发ServletContextEvent 事件 当此事件执行时，就会被ServletContextListener 监听器监听到，会调用他的 contextInitialized(ServletContextEvent sce) 方法，通过sce 可以获取ServletContext 实例，初始化一些数据，例如缓存的应用，如，创建数据库连接，读取数据库数据，通过setAttribute(“”,obj) 方法设置数据，然后就是可通过servlet 获取servletContext 的实例，通过getAttribute(“”) 获取设置的数据
实现代码：
public class MyContextListener implements ServletContextListener { private ServletContext context = null; public void contextInitialized(ServletContextEvent event) { context = event.getServletContext(); User user = DatabaseManager.getUserById(1); context.setAttribute("user1", user); } public void contextDestroyed(ServletContextEvent event) { User user = (User)context.getAttribute("user1"); DatabaseManager.updateUserData(user); this.context = null; } }如果是web 项目 最后一步是使 ServletContext 生效，需要在web.xml 中配置监听器，并且web.xml 把它放在正确的WEB-INF/classes目录下，
MyServletContextListener
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