文章目录 JavaWeb 三大组件之监听器 Listener Listener JavaWeb 的监听器 ServletContextListener 监听器 ServletContextAttributeListener 监听器 其它监听器-使用较少 HttpSessionListener 监听器 HttpSessionAttributeListener 监听器 ServletRequestListener 监听器 ServletRequestAttributeListener 监听器 HttpSessionBindingListener 感知监听器 HttpSessionActivationListener 感知监听器 JavaWeb 三大组件之 过滤器 Filter 为啥要过滤器-需求示意图 过滤器介绍 Filter 过滤器基本原理 需求 Filter 过滤器生命周期 FilterConfig FilterChain 过滤器链 基本原理示意图 需求: FilterChain 注意事项和细节 Filter 作业练习
JavaWeb 三大组件之监听器 Listener
Listener
Listener 监听器它是 JavaWeb 的三大组件之一。JavaWeb 的三大组件分别是:Servlet 程序、Listener 监听器、Filter 过滤器 Listener 是 JavaEE 的规范,就是接口 监听器的作用是,监听某种变化(一般就是对象创建/销毁, 属性变化), 触发对应方法完成相应的任务 JavaWeb 中的监听器(共八个), 目前最常用的是 ServletContextListener,
JavaWeb 的监听器
ServletContextListener 监听器
作用:监听 ServletContext 创建或销毁(当我们 Web 应用启动时,就会创建 ServletContext),即生命周期监听,应用场景(1)加载初始化的配置文件;比如 spring 的配置文件 (2)任务调度(配合定时器 Timer/TimerTask) 相关方法
@WebListener ( )
public class LGQServletContextListener implements ServletContextListener { @Override public void contextInitialized ( ServletContextEvent servletContextEvent) { ServletContext servletContext = servletContextEvent. getServletContext ( ) ; System . out. println ( "监听器监听到servletContext被创建" + servletContext) ; } @Override public void contextDestroyed ( ServletContextEvent servletContextEvent) { ServletContext servletContext = servletContextEvent. getServletContext ( ) ; System . out. println ( "监听器监听到servletContext被销毁" + servletContextEvent) ; }
}
ServletContextAttributeListener 监听器
作用:监听 ServletContext 属性变化 相关方法
@WebListener
public class LGQServletContextAttributeListener implements ServletContextAttributeListener { @Override public void attributeAdded ( ServletContextAttributeEvent servletContextAttributeEvent) { System . out. println ( "监听到属性被创建:" + servletContextAttributeEvent. getName ( ) + " " + servletContextAttributeEvent. getValue ( ) ) ; } @Override public void attributeRemoved ( ServletContextAttributeEvent servletContextAttributeEvent) { System . out. println ( "监听到属性被删除:" + servletContextAttributeEvent. getName ( ) + " " + servletContextAttributeEvent. getValue ( ) ) ; } @Override public void attributeReplaced ( ServletContextAttributeEvent servletContextAttributeEvent) { System . out. println ( "监听到属性被替换:" + servletContextAttributeEvent. getName ( ) + " " + servletContextAttributeEvent. getValue ( ) ) ; }
}
@WebServlet ( urlPatterns = "/ServletContextAttributeServlet" )
public class ServletContextAttributeServlet extends HttpServlet { @Override protected void doPost ( HttpServletRequest req, HttpServletResponse resp) throws ServletException , IOException { ServletContext servletContext = req. getServletContext ( ) ; servletContext. setAttribute ( "123" , "aegf" ) ; servletContext. setAttribute ( "124" , "t43wt" ) ; servletContext. setAttribute ( "123" , "123" ) ; servletContext. removeAttribute ( "124" ) ; } @Override protected void doGet ( HttpServletRequest req, HttpServletResponse resp) throws ServletException , IOException { doPost ( req, resp) ;