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.
- *
- * <p>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.
- *
- * <p>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,
- <listener>
- <listener-class>MyServletContextListener</listener-class>
- </listener>