ClassPathXmlApplicationContext classPathXmlApplicationContext =
      new ClassPathXmlApplicationContext("coderLi.xml");
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<bean class="com.demo.data.Cat" id="cat"/>
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public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
   this(new String[] {configLocation}, true, null);
}
public ClassPathXmlApplicationContext(
  String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
  throws BeansException {
  super(parent);
  setConfigLocations(configLocations);
  if (refresh) {
    refresh();
  }
}
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public void setConfigLocations(@Nullable String... locations) {
   if (locations != null) {
      Assert.noNullElements(locations, "Config locations must not be null");
      this.configLocations = new String[locations.length];
      for (int i = 0; i < locations.length; i++) {
         // 解释给定路径，比如说 路径中包含某些特殊符号 ${var}
         this.configLocations[i] = resolvePath(locations[i]).trim();
      }
   }
   else {
      this.configLocations = null;
   }
}
protected String resolvePath(String path) {
  return getEnvironment().resolveRequiredPlaceholders(path);
}
@Override
public ConfigurableEnvironment getEnvironment() {
  if (this.environment == null) {
    this.environment = createEnvironment();
  }
  return this.environment;
}
protected ConfigurableEnvironment createEnvironment() {
  return new StandardEnvironment();
}
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@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      prepareRefresh();
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
      prepareBeanFactory(beanFactory);
      try {
         postProcessBeanFactory(beanFactory);
         invokeBeanFactoryPostProcessors(beanFactory);
         registerBeanPostProcessors(beanFactory);
         initMessageSource();
         initApplicationEventMulticaster();
         onRefresh();
         registerListeners();
         finishBeanFactoryInitialization(beanFactory);
         finishRefresh();
      } catch (BeansException ex) {
         destroyBeans();
         cancelRefresh(ex);
         throw ex;
      } finally {
         resetCommonCaches();
      }
   }
}
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protected void prepareRefresh() {
  // .......
  // 初始化属性源
   initPropertySources();
  // 对属性进行验证
   getEnvironment().validateRequiredProperties();
}
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@Override
protected void initPropertySources() {
   ConfigurableEnvironment env = getEnvironment();
   if (env instanceof ConfigurableWebEnvironment) {
      ((ConfigurableWebEnvironment) env).initPropertySources(this.servletContext, null);
   }
}
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@Override
protected final void refreshBeanFactory() throws BeansException {
  .........
   try {
      // 创建 DefaultListableBeanFactory
      DefaultListableBeanFactory beanFactory = createBeanFactory();
      // 为了序列化的时候、指定 id
      beanFactory.setSerializationId(getId());
      // 定制 beanFactory
      customizeBeanFactory(beanFactory);
      loadBeanDefinitions(beanFactory);
      synchronized (this.beanFactoryMonitor) {
         this.beanFactory = beanFactory;
      }
   }
   catch (IOException ex) {
    .....
   }
}
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protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
   PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
   if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
      beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
      beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
   }
}
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protected void initMessageSource() {
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
      this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
       if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
         HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
         if (hms.getParentMessageSource() == null) {
            hms.setParentMessageSource(getInternalParentMessageSource());
         }
      }
   } else {
      DelegatingMessageSource dms = new DelegatingMessageSource();
      dms.setParentMessageSource(getInternalParentMessageSource());
      this.messageSource = dms;
      beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
   }
}
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protected void initApplicationEventMulticaster() {
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
      this.applicationEventMulticaster =
            beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
   } else {
      this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
      beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
   }
}
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protected void registerListeners() {
   for (ApplicationListener<?> listener : getApplicationListeners()) {
      getApplicationEventMulticaster().addApplicationListener(listener);
   }
   String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
   for (String listenerBeanName : listenerBeanNames) {
      getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
   }
   Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
   this.earlyApplicationEvents = null;
   if (earlyEventsToProcess != null) {
      for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
         getApplicationEventMulticaster().multicastEvent(earlyEvent);
      }
   }
}
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