如何在flink中计算历史累计数据

import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.api.windowing.assigners.TumblingProcessingTimeWindows;
import org.apache.flink.streaming.api.windowing.time.Time;

public class HistoryCumulativeCalculation {
    public static void main(String[] args) throws Exception {
        // 创建执行环境
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        // 创建数据流
        DataStream<Tuple2<String, Integer>> dataStream = env.fromElements(
                new Tuple2<>("A", 1),
                new Tuple2<>("B", 2),
                new Tuple2<>("A", 3),
                new Tuple2<>("B", 4),
                new Tuple2<>("A", 5)
        );

        // 使用窗口操作，将数据划分为滚动窗口，窗口大小为2秒
        DataStream<Tuple2<String, Integer>> resultStream = dataStream
                .keyBy(0)
                .window(TumblingProcessingTimeWindows.of(Time.seconds(2)))
                .reduce(new ReduceFunction<Tuple2<String, Integer>>() {
                    @Override
                    public Tuple2<String, Integer> reduce(Tuple2<String, Integer> value1, Tuple2<String, Integer> value2) throws Exception {
                        // 将历史累计数据与当前窗口中的数据进行累加
                        return new Tuple2<>(value1.f0, value1.f1 + value2.f1);
                    }
                });

        // 打印结果
        resultStream.print();

        // 执行任务
        env.execute("History Cumulative Calculation");
    }
}