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Flink 系例 之 Fold

慕容聪
2023-12-01

Fold算子:将数据流的每一次输出进行滚动叠加,合并输出结果

示例环境

java.version: 1.8.x
flink.version: 1.11.1

示例数据源(项目码云下载)

Flink 系例 之 搭建开发环境与数据

Fold.java

import com.flink.examples.DataSource;
import org.apache.flink.api.common.functions.FoldFunction;
import org.apache.flink.api.java.functions.KeySelector;
import org.apache.flink.api.java.tuple.Tuple3;
import org.apache.flink.streaming.api.datastream.KeyedStream;
import org.apache.flink.streaming.api.datastream.SingleOutputStreamOperator;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import java.util.List;

/**
 * @Description Fold算子:将数据流的每一次输出进行滚动叠加,合并输出结果
 * (与Reduce的区别是,Reduce是拿前一次聚合结果累加后一次的并输出数据流;Fold是直接将当前数据对象追加到前一次叠加结果上并输出数据流)
 */
public class Fold {
    /**
     * 遍历集合,分区打印每一次滚动叠加的结果(示例:按性别分区,按排序,未位追加输出)
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {
        final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
        env.setParallelism(4);
        List<Tuple3<String,String,Integer>> tuple3List = DataSource.getTuple3ToList();
        //注意:使用Integer进行分区时,会导致分区结果不对,转换成String类型输出key即可正确输出
        KeyedStream<Tuple3<String,String,Integer>, String> keyedStream = env.fromCollection(tuple3List).keyBy(new KeySelector<Tuple3<String,String,Integer>, String>() {
            @Override
            public String getKey(Tuple3<String, String, Integer> tuple3) throws Exception {
                //f1为性别字段,以相同f1值(性别)进行分区
                return String.valueOf(tuple3.f1);
            }
        });
        SingleOutputStreamOperator<String> result = keyedStream.fold("同学:", new FoldFunction<Tuple3<String, String, Integer>, String>() {
            @Override
            public String fold(String s, Tuple3<String, String, Integer> tuple3) throws Exception {
                if (s.startsWith("男") || s.startsWith("女")){
                    return s + tuple3.f0 + "、";
                } else {
                    return (tuple3.f1.equals("man") ? "男" : "女") + s + tuple3.f0 + "、";
                }
            }
        });
        result.print();
        env.execute("flink Fold job");
    }
}

打印结果

2> 男同学:张三、
2> 男同学:张三、王五、
2> 男同学:张三、王五、吴八、
1> 女同学:李四、
1> 女同学:李四、刘六、
1> 女同学:李四、刘六、伍七、
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