flink-reduce

一.背景

     有时候我们需要过滤数据，有些中间数据是不需要的，比如场景：

     binlog 数据更新的时候，我们仅仅需要最新数据。会根据ID 分组，然后取version 最大的一条，存储

 

二.简单实例

  

@Data
@ToString
public class Order {
    // 主键id
    private Integer id;
    // 版本
    private Integer version;
    private Timestamp mdTime;

    public Order(int id, Integer version) {
        this.id = id;
        this.version = version;
        this.mdTime = new Timestamp(System.currentTimeMillis());
    }

    public Order() {
    }
}

 

 

public class OrderSource implements SourceFunction<Order> {
    Random random = new Random();

    @Override
    public void run(SourceContext<Order> ctx) throws Exception {
        while (true) {
            TimeUnit.MILLISECONDS.sleep(100);
            // 为了区分，我们简单生0~2的id, 和版本0~99
            int id = random.nextInt(3);
            Order o = new Order(id, random.nextInt(100));
            ctx.collect(o);
        }
    }
    @Override
    public void cancel() {

    }
}

 

public class ReduceApp {
    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
        env.setParallelism(1);
        env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);
        DataStream<Order> userInfoDataStream = env.addSource(new OrderSource());

        DataStream<Order> timedData = userInfoDataStream.assignTimestampsAndWatermarks(new AscendingTimestampExtractor<Order>() {
            @Override
            public long extractAscendingTimestamp(Order element) {
                return element.getMdTime().getTime();
            }
        });

        SingleOutputStreamOperator<Order> reduce = timedData
                .keyBy("id")
                .timeWindow(Time.seconds(10), Time.seconds(5))
                .reduce((ReduceFunction<Order>) (v1, v2) -> v1.getVersion() >= v2.getVersion() ? v1 : v2);

        reduce.print();
        env.execute("test");
    }
}

 

结果：

Order(id=2, version=97, mdTime=2019-03-11 17:39:34.052)

Order(id=0, version=99, mdTime=2019-03-11 17:39:32.913)

Order(id=1, version=96, mdTime=2019-03-11 17:39:34.155)

Order(id=2, version=97, mdTime=2019-03-11 17:39:34.052)

Order(id=1, version=96, mdTime=2019-03-11 17:39:34.155)

Order(id=0, version=99, mdTime=2019-03-11 17:39:32.913)

 

这个会对同一个窗口做过滤，比如同步到另一个mysql,hdfs，就能减少数据量