apollo-client/src/main/java/com/ctrip/framework/apollo/spring/util/SpringInjector.java/SpringModule/configure
class SpringModule:    @Override
    protected void configure() {
      bind(PlaceholderHelper.class).in(Singleton.class);
      bind(ConfigPropertySourceFactory.class).in(Singleton.class);
      bind(SpringValueRegistry.class).in(Singleton.class);
    }