Flink Window那些事——ReduceFunction窗口函数

ReduceFunction含义
ReduceFunction定义了如何把两个输入的元素进行合并来生成相同类型的输出元素的过程，Flink使用ReduceFunction来对窗口中的元素进行增量聚合

package com.lynch.stream.window;

import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.java.tuple.Tuple3;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;

/**
 * 测试ReduceFunction
 *
 */
public class TestReduceFunctionOnWindow {
    public static void main(String[] args) throws Exception{
        //获取执行环境
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        //读取数据
        DataStream<Tuple3<String,String,Integer>> input = env.fromElements(ENGLISH);

        //keyBy(0) 计算班级总成绩，下标0表示班级
        //countWindow(2) 根据元素个数对数据流进行分组切片，达到2个，触发窗口进行计算
        DataStream<Tuple3<String,String,Integer>>  totalPoints = input.keyBy(0).countWindow(2).reduce(new ReduceFunction<Tuple3<String, String, Integer>>() {
            @Override
            public Tuple3<String, String, Integer> reduce(Tuple3<String, String, Integer> value1, Tuple3<String, String, Integer> value2) throws Exception {
                //效果如下：
                //(class1,张三,100)
                //(class1,李四,30)
                //==============
                System.out.println("" + value1);
                System.out.println("" + value2);
                System.out.println("==============");
                return new Tuple3<>(value1.f0, value1.f1, value1.f2+value2.f2);
            }
        });

        //输出结果
        //效果如下：
        //2> (class1,张三,130)
        totalPoints.print();

        env.execute("TestReduceFunctionOnWindow");
    }

    /**
     * 定义班级的三元数组
     */
    public static final Tuple3[] ENGLISH = new Tuple3[]{
            //班级 姓名 成绩
            Tuple3.of("class1","张三",100),
            Tuple3.of("class1","李四",30),
            Tuple3.of("class1","王五",70),
            Tuple3.of("class2","赵六",50),
            Tuple3.of("class2","小七",40),
            Tuple3.of("class2","小八",10),
    };
    
}

ReduceFunction执行返回结果

(class2,赵六,50)
(class2,小七,40)
==============

1> (class2,赵六,90)

(class1,张三,100)
(class1,李四,30)
==============

2> (class1,张三,130)