如何保存DoFn中的变量，以便以后在流水线中使用？

import org.apache.beam.sdk.state.BagState;
import org.apache.beam.sdk.state.StateSpec;
import org.apache.beam.sdk.transforms.DoFn;
import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
import org.apache.beam.sdk.values.KV;

public class MyDoFn extends DoFn<KV<String, Integer>, String> {
  // 定义状态描述符
  private final StateSpec<BagState<Integer>> stateSpec = StateSpecs.bag();

  // 注册状态
  @StateId("myState")
  private final StateSpec<ValueState<Integer>> myStateSpec = StateSpecs.value();

  @ProcessElement
  public void processElement(
      @Element KV<String, Integer> element,
      @Timestamp Instant timestamp,
      BoundedWindow window,
      @StateId("myState") ValueState<Integer> myState,
      @StateId("myBagState") BagState<Integer> myBagState,
      OutputReceiver<String> outputReceiver) {

    // 使用状态
    Integer myValue = myState.read();
    myState.write(element.getValue() + 1);

    myBagState.add(element.getValue());

    // ...
  }
}