Spring源码1——从启动ContextLoaderListener看Spring
ContextLoaderListener的定义：
public class ContextLoaderListener extends ContextLoader implements ServletContextListener{}
1,实现的接口 ServletContextListenter
ServletContextListenter是J2ee Servlet标准的一部分，用于监听ServletContext的启动和销毁；
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);
}
EventListener是事件标志接口
/**
* A tagging interface that all event listener interfaces must extend.
* @since JDK1.1
*/
public interface EventListener {
}
Servlet生命周期
Web容器启动 加载Web.xml中配置的Servlet 第一次开始调用 开始应用期间的一次初始化； 当应用停止 Servlet调用Destoryed；
ServletContext
代表着web应用一个应用只有一个记录整个应用的信息；
总结：ContextLoadListener实现ServletContextListener是为了在应用启动或者关闭时做一些必要的工作；
/**
* 重写了ServletContext初始化监听
* Initialize the root web application context.
*/
@Override
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}
/**
*重写了ServletContext销毁监听
* Close the root web application context.
*/
@Override
public void contextDestroyed(ServletContextEvent event) {
closeWebApplicationContext(event.getServletContext());
ContextCleanupListener.cleanupAttributes(event.getServletContext());
}
2，继承ContextLoader
主要用于创建WebApplicationContext；
可以在通过web.xml 的initParam来指定默认的WebApplicationContext的实现类就会采用XmlWebApplicationContext来当做默认；WebApplicationContext是存储在ServletContext中的应用级变量；并且是唯一的！
在创建过程：
1，获得加载类 CurrTheadClassLoader 或者 ClassUtils.class.getClassLoader(); 或者 ClassLoader.getSystemClassLoader();
2，开始通过加载类获得Class
3，通过Class的反射构造 newInstance