Spring-ContextLoaderListener

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/*
* Copyright 2002-2011 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
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package org.springframework.web.context;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
* Bootstrap listener to start up and shut down Spring's root {@link WebApplicationContext}.

* Simply delegates to {@link ContextLoader} as well as to {@link ContextCleanupListener}.

引动程序监听器，它监听启动和关闭Spring的Root（即Web应用的环境/上下文）的事件。

这个监听动作委托给ContextLoader，ContextCleanupListerner的监听也是这样实现的。

*
* This listener should be registered after
* {@link org.springframework.web.util.Log4jConfigListener}

* in <code>web.xml</code>, if the latter is used.

这个监听器，应该放到Log4jConfigListener后面，如果在web.xml中配置了这个监听器。

*
* As of Spring 3.1, {@code ContextLoaderListener} supports injecting the root web
* application context via the {@link #ContextLoaderListener(WebApplicationContext)}
* constructor, allowing for programmatic configuration in Servlet 3.0+ environments. See
* {@link org.springframework.web.WebApplicationInitializer} for usage examples.
*
* @author Juergen Hoeller
* @author Chris Beams
* @since 17.02.2003
* @see org.springframework.web.WebApplicationInitializer
* @see org.springframework.web.util.Log4jConfigListener
*/
public class ContextLoaderListener extends ContextLoader implements ServletContextListener {

 private ContextLoader contextLoader;

 /**
 * Create a new {@code ContextLoaderListener} that will create a web application
 * context based on the "contextClass" and "contextConfigLocation" servlet
 * context-params. See {@link ContextLoader} superclass documentation for details on

* default values for each.

创建一个新的ContextLoaderListener(环境载入/加载监听器)，这个监听器会创建一个web应用环境/上下文，

这个上下文基于contextClass和contextConfigLocation这两个Servlet环境/上下文参数。具体参见该类的父类ContextLoader中

的对每个的默认值的详细的描述。

* This constructor is typically used when declaring {@code ContextLoaderListener}
* as a {@code <listener>} within {@code web.xml}, where a no-arg constructor is

* required.

当在web.xml中，如果ContextLoaderListener以Listener（用<listener>标签声明）在web.xml进行了声明，在web.xml

中，就会需要一个无参数的构造器，这个构造器就会被用到。

* The created application context will be registered into the ServletContext under
 * the attribute name {@link WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE}
 * and the Spring application context will be closed when the {@link #contextDestroyed}
 * lifecycle method is invoked on this listener.
 * @see ContextLoader
 * @see #ContextLoaderListener(WebApplicationContext)
 * @see #contextInitialized(ServletContextEvent)
 * @see #contextDestroyed(ServletContextEvent)
 */
 public ContextLoaderListener() {
 }

 /**
 * Create a new {@code ContextLoaderListener} with the given application context. This
 * constructor is useful in Servlet 3.0+ environments where instance-based
 * registration of listeners is possible through the {@link ServletContext#addListener}

* API.

使用指定的application context创建一个ContextLoaderListener。这个构造器在Servlet3.0+的环境中非常有用，

这个Servlet3.0+环境中，通过ServletContext的addListerner方法，基于实例的监听器注册是可能的。

* The context may or may not yet be {@linkplain

* ConfigurableApplicationContext#refresh() refreshed}.

这个环境/上下文可能，也可能没有被刷新(可以参考ConfigurableApplicationContext的refresh方法)。

If it (a) is an implementation

* of {@link ConfigurableWebApplicationContext} and (b) has not

* already been refreshed (the recommended approach), then the following will occur:

如果，它实现了ConfigurableWebApplicationContext接口，并且没有刷新（推荐的方法），然后，下面的事情会发生：

* <ul>
* <li>If the given context has not already been assigned an {@linkplain

* ConfigurableApplicationContext#setId id}, one will be assigned to it</li>

如果，这个给定的context环境／上下文)还没有设置一个id,那么一个Id给它(context)设置。

* <li>{@code ServletContext} and {@code ServletConfig} objects will be delegated to

* the application context</li>

ServletContext和ServletConfig这些对象（的功能）会被委托给这个application环境(上下文)

* <li>{@link #customizeContext} will be called</li>

ContextLoader.customizeContext(javax.servlet.ServletContext, org.springframework.web.context.ConfigurableWebApplicationContext) 会被调用。

* <li>Any {@link ApplicationContextInitializer}s specified through the

* "contextInitializerClasses" init-param will be applied.</li>

任何ApplicationContextInitializerS指定的，通过contextInitializerClasses的init-param会被应用上。

* <li>{@link ConfigurableApplicationContext#refresh refresh()} will be called</li>

ConfigurableApplication的refresh方法会被调用。

* </ul>
 * If the context has already been refreshed or does not implement
 * {@code ConfigurableWebApplicationContext}, none of the above will occur under the
 * assumption that the user has performed these actions (or not) per his or her

* specific needs.

如果，这个context(环境/上下文)已经被刷新过，或者没有实现ConfigurableWebApplicationContext接口的话，

以上的事情都不会发生，在一个假设下，这个假设是永恒已经执行了这些动作（或者没有）根据用户的特定的需求。

* See {@link org.springframework.web.WebApplicationInitializer} for usage examples.

请看WebApplicationInitializer的使用例子。

* In any case, the given application context will be registered into the
 * ServletContext under the attribute name {@link
 * WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE} and the Spring
 * application context will be closed when the {@link #contextDestroyed} lifecycle

* method is invoked on this listener.

（In any case, the given application context will be registered into the ServletContext under the attribute nameWebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE and the Spring application context will be closed when thecontextDestroyed(javax.servlet.ServletContextEvent) lifecycle method is invoked on this listener.）

在任何情况下，这个传入的application的环境/上下文会被注册到ServletContext中，在这个WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE上，并且，Spring Application的环境/上下文会关闭

当这个监听器的contextDestroyed的方法被调用时。

   * @param context the application context to manage
   * @see #contextInitialized(ServletContextEvent)
   * @see #contextDestroyed(ServletContextEvent)
   */
   public ContextLoaderListener(WebApplicationContext context) {
       super(context);
   }

   /**

* Initialize the root web application context.

初始化root web appliation 环境/上下文。

   */
   public void contextInitialized(ServletContextEvent event) {
       this.contextLoader = createContextLoader();
       if (this.contextLoader == null) {
           this.contextLoader = this;
       }
       this.contextLoader.initWebApplicationContext(event.getServletContext());
   }

   /**

* Create the ContextLoader to use. Can be overridden in subclasses.

创建一个会用到的ContextLoader，在子类中可以被覆盖。

   * @return the new ContextLoader
   * @deprecated in favor of simply subclassing ContextLoaderListener itself
   * (which extends ContextLoader, as of Spring 3.0)
   */
   @Deprecated
   protected ContextLoader createContextLoader() {
       return null;
   }

   /**

* Return the ContextLoader used by this listener.

返回这个listerner用到的这个ContextLoader。

   * @return the current ContextLoader
   * @deprecated in favor of simply subclassing ContextLoaderListener itself
   * (which extends ContextLoader, as of Spring 3.0)
   */
   @Deprecated
   public ContextLoader getContextLoader() {
       return this.contextLoader;
   }

   /**

* Close the root web application context.

关闭root web application 环境/上下文。

   */
   public void contextDestroyed(ServletContextEvent event) {
       if (this.contextLoader != null) {
           this.contextLoader.closeWebApplicationContext(event.getServletContext());
       }
       ContextCleanupListener.cleanupAttributes(event.getServletContext());
   }

}

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