ServletContextListener 详解

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>

--------------------- 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