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
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 );
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ServletContext servletContext;
public void contextInitialized(ServletContextEvent sce)
{
servletContext = sce.getServletContext();
}
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
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;
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filterConfig.getServletContext()
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
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 config a <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;
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getServletConfig().getServletContext()
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)。
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)。