apollo-client/src/main/java/com/ctrip/framework/apollo/internals/DefaultInjector.java/DefaultInjector/getInstance
class DefaultInjector:  @Override
  public <T> T getInstance(Class<T> clazz) {
    try {
      for (ApolloInjectorCustomizer customizer : m_customizers) {
        T instance = customizer.getInstance(clazz);
        if (instance != null) {
          return instance;
        }
      }
      return m_injector.getInstance(clazz);
    } catch (Throwable ex) {
      Tracer.logError(ex);
      throw new ApolloConfigException(
          String.format("Unable to load instance for %s!", clazz.getName()), ex);
    }
  }