ApplicationContextInitializer接口的源码解读

ApplicationContextInitializer接口的作用：

可以在spring的上下文ApplicationContext初始化之前，即wac.refresh()之前修改spring上下文属性。源码如下

configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac){
.
.
.

postProcessWebApplicationContext(wac);
applyInitializers(wac);
wac.refresh();
}

applyInitializers(wac);

protected void applyInitializers(ConfigurableApplicationContext wac) {
   String globalClassNames = getServletContext().getInitParameter(ContextLoader.GLOBAL_INITIALIZER_CLASSES_PARAM);
   if (globalClassNames != null) {
      for (String className : StringUtils.tokenizeToStringArray(globalClassNames, INIT_PARAM_DELIMITERS)) {
         this.contextInitializers.add(loadInitializer(className, wac));
      }
   }

   if (this.contextInitializerClasses != null) {
      for (String className : StringUtils.tokenizeToStringArray(this.contextInitializerClasses, INIT_PARAM_DELIMITERS)) {
         this.contextInitializers.add(loadInitializer(className, wac));
      }
   }

   AnnotationAwareOrderComparator.sort(this.contextInitializers);
   for (ApplicationContextInitializer<ConfigurableApplicationContext> initializer : this.contextInitializers) {
      initializer.initialize(wac);
   }
}

String globalClassNames = getServletContext().getInitParameter(ContextLoader.GLOBAL_INITIALIZER_CLASSES_PARAM);

这行代码意思是从servlet上下文中获取属性，所以必须保证在web.xml中必须配置了该属性，且必须有spring配置文件加载，即通过监听方式加载配置文件的方式。

<context-param>
  <param-name>globalInitializerClasses</param-name>
  <param-value>com.zhuguang.jack.applicationContextInitializer.MyApplicationContextInitializer</param-value>
</context-param>

如果没有

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

监听加载配置文件的方式，即使配置了该属性，代码中也获取不到。切记，切记

loadInitializer(className, wac)把web.xml中配置的类实例化

for (ApplicationContextInitializer<ConfigurableApplicationContext> initializer : this.contextInitializers) { initializer.initialize(wac); }

调用initialize方法，可以对spring上下文进行修改