private FactorySupplier getSupplier() {
    switch (singletonID) {
      case 0:
        return NONSingleton.INSTANCE;
      case 1:
        return DTDSingleton.INSTANCE;
      case 2:
        return XSDSingleton.INSTANCE;
    }
    throw new IllegalStateException("Unknown singletonID: " + singletonID);
  }
private FactorySupplier getSupplier()