apollo-client/src/main/java/com/ctrip/framework/apollo/spi/DefaultConfigFactoryManager.java/DefaultConfigFactoryManager/getFactory
class DefaultConfigFactoryManager:  @Override
  public ConfigFactory getFactory(String namespace) {
    // step 1: check hacked factory
    ConfigFactory factory = m_registry.getFactory(namespace);

    if (factory != null) {
      return factory;
    }

    // step 2: check cache
    factory = m_factories.get(namespace);

    if (factory != null) {
      return factory;
    }

    // step 3: check declared config factory
    factory = ApolloInjector.getInstance(ConfigFactory.class, namespace);

    if (factory != null) {
      return factory;
    }

    // step 4: check default config factory
    factory = ApolloInjector.getInstance(ConfigFactory.class);

    m_factories.put(namespace, factory);

    // factory should not be null
    return factory;
  }