ServletContextListener 详解

1.首先来看一看源码 该类的源码

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   public interface ServletContextListener extends EventListener {
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   /**
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   * Receives notification that the web application initialization
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   * process is starting.
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   *
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   * <p>All ServletContextListeners are notified of context
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   * initialization before any filters or servlets in the web
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   * application are initialized.
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    *
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    * @param sce the ServletContextEvent containing the ServletContext
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    * that is being initialized
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    */
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    public void contextInitialized(ServletContextEvent sce);
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    /**
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    * Receives notification that the ServletContext is about to be
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    * shut down.
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    *
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    * <p>All servlets and filters will have been destroyed before any
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    * ServletContextListeners are notified of context
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    * destruction.
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    *
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    * @param sce the ServletContextEvent containing the ServletContext
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    * that is being destroyed
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    */
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    public void contextDestroyed(ServletContextEvent sce);
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    }

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：

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   public class MyContextListener implements ServletContextListener {
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   private ServletContext context = null;
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   public void contextInitialized(ServletContextEvent event) {
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   context = event.getServletContext();
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   User user = DatabaseManager.getUserById(1);
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   context.setAttribute("user1", user);
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   }
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    public void contextDestroyed(ServletContextEvent event) {
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    User user = (User)context.getAttribute("user1");
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    DatabaseManager.updateUserData(user);
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    this.context = null;
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    }
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    }

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，

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   <listener>
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   <listener-class>MyServletContextListener</listener-class>
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   </listener>

--------------------- 本文来自 为了那份宁静 的CSDN 博客 ，全文地址请点击：https://blog.csdn.net/linhaiguo/article/details/50867376?utm_source=copy