apollo-client/src/main/java/com/ctrip/framework/apollo/internals/DefaultInjector.java/DefaultInjector/configure
class DefaultInjector:    @Override
    protected void configure() {
      bind(ConfigManager.class).to(DefaultConfigManager.class).in(Singleton.class);
      bind(ConfigFactoryManager.class).to(DefaultConfigFactoryManager.class).in(Singleton.class);
      bind(ConfigRegistry.class).to(DefaultConfigRegistry.class).in(Singleton.class);
      bind(ConfigFactory.class).to(DefaultConfigFactory.class).in(Singleton.class);
      bind(ConfigUtil.class).in(Singleton.class);
      bind(HttpClient.class).to(DefaultHttpClient.class).in(Singleton.class);
      bind(ConfigServiceLocator.class).in(Singleton.class);
      bind(RemoteConfigLongPollService.class).in(Singleton.class);
      bind(YamlParser.class).in(Singleton.class);
      bind(PropertiesFactory.class).to(DefaultPropertiesFactory.class).in(Singleton.class);
    }