code: public void initFromProcessEngineConfiguration(ProcessEngineConfigurationImpl processEngineConfiguration, String resourceName) {
      this.resourceName = resourceName;
  
      setDataSource(processEngineConfiguration.getDataSource());
  
      initDataSource();
      initCommandContextFactory();
      initTransactionFactory();
      initTransactionContextFactory();
      initCommandExecutors();
      initIdentityProviderSessionFactory();
      initSqlSessionFactory();
      initSessionFactories();
    }
docs: initialize the {@link ProcessEngineConfiguration} from an existing one,
  just using the database settings and initialize the database / MyBatis
  stuff.