strust2中是如何初始化container并且使其全局单例？

StrutsPrepareAndExecuteFilter

   protected PrepareOperations prepare;
    protected ExecuteOperations execute;

Dispatcher dispatcher = init.initDispatcher(config);

      init()

      Container container = init_PreloadConfiguration();

   private Container init_PreloadConfiguration() {
        Configuration config = configurationManager.getConfiguration();
        Container container = config.getContainer();

        boolean reloadi18n = Boolean.valueOf(container.getInstance(String.class, StrutsConstants.STRUTS_I18N_RELOAD));
        LocalizedTextUtil.setReloadBundles(reloadi18n);

        return container;
    }

       Configuration config = configurationManager.getConfiguration();
        Container container = config.getContainer();

  public synchronized Configuration getConfiguration() {
        if (configuration == null) {
            setConfiguration(createConfiguration(defaultFrameworkBeanName));
            try {
                configuration.reloadContainer(getContainerProviders());
            } catch (ConfigurationException e) {
                setConfiguration(null);
                throw new ConfigurationException("Unable to load configuration.", e);
            }
        } else {
            conditionalReload(configuration.getContainer());
        }

        return configuration;
    }

....

 prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);
 execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);