code: public static ApplicationContext get() {
          ClassLoader classLoader = getContextClassLoader();
          while (classLoader != null) {
              ApplicationContext applicationContext = contextMap.get(classLoader);
              if (applicationContext != null) {
                  return applicationContext;
              }
              classLoader = classLoader.getParent();
          }
          return null;
      }
docs: Returns the {@link ApplicationContext} bound to the current context class loader or any of
  its parent class loaders. Walking up the class loader hierarchy is required to support
  special class loader scenarios like Spring Boot's reloading mechanism.