Servlet,Listener和Filter如何获取ServletContext(既application)
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Listener的项目上下文（既ServletContext既application）是从event中获取的，event是Listener和容器之间交流的中间人
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public interface ServletContextListener extends EventListener {/** ** Notification that the web application initialization ** process is starting. ** All ServletContextListeners are notified of context ** initialization before any filter or servlet in the web ** application is initialized. */ public void contextInitialized ( ServletContextEvent sce );-------------------------------------------- ServletContext servletContext; public void contextInitialized(ServletContextEvent sce) { servletContext = sce.getServletContext(); }??
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而Filter的项目上下文（既ServletContext既application）是从FilterConfig中获取的，FilterConfig是Filter和容器之间交流的中间人
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public interface Filter {/** * Called by the web container to indicate to a filter that it is being placed into* service. The servlet container calls the init method exactly once after instantiating the* filter. The init method must complete successfully before the filter is asked to do any* filtering work. <br><br> * The web container cannot place the filter into service if the init method either<br> * 1.Throws a ServletException <br> * 2.Does not return within a time period defined by the web container */public void init(FilterConfig filterConfig) throws ServletException;------------------------filterConfig.getServletContext()?
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而Servlet的项目上下文（既ServletContext既application）是从ServletConfig中获取的，ServletConfig是Servlet和容器之间交流的中间人
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public interface Servlet { /** * Called by the servlet container to indicate to a servlet that the * servlet is being placed into service. * * <p>The servlet container calls the <code>init</code> * method exactly once after instantiating the servlet. * The <code>init</code> method must complete successfully * before the servlet can receive any requests. * * <p>The servlet container cannot place the servlet into service * if the <code>init</code> method * <ol> * <li>Throws a <code>ServletException</code> * <li>Does not return within a time period defined by the Web server * </ol> * * * @param configa <code>ServletConfig</code> object *containing the servlet's * configuration and initialization parameters * * @exception ServletException if an exception has occurred that *interferes with the servlet's normal *operation * * @see UnavailableException * @see #getServletConfig * */ public void init(ServletConfig config) throws ServletException; --------------------------------------- getServletConfig().getServletContext()??
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我们的应用程序组件只能被动的遵守一定的规则，和容器打交道，和其他组件通信，也必须借助于容器的力量。这里面其实已经有一点控制反转的味道，既然是组件生活在容器中，就必须被动的接受容器喂给他吃的东西，不能(要)自己创造（new）。
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Spring之所以称为容器（号称轻量级），就是因为被他控制的组件，被动的吃他喂过来的东西，不能(要)自己创造（new）。