一、Flink窗口函数

前面指定了窗口的分配器, 接着我们需要来指定如何计算, 这事由window function来负责. 一旦窗口关闭, window function 去计算处理窗口中的每个元素.
window function 可以是ReduceFunction,AggregateFunction,or ProcessWindowFunction中的任意一种.
ReduceFunction,AggregateFunction更加高效, 原因就是Flink可以对到来的元素进行增量聚合 . ProcessWindowFunction 可以得到一个包含这个窗口中所有元素的迭代器, 以及这些元素所属窗口的一些元数据信息.
ProcessWindowFunction不能被高效执行的原因是Flink在执行这个函数之前, 需要在内部缓存这个窗口上所有的元素。
除了一些简单聚合，比如 sum,max,min,maxBay,minBay ，有以下窗口聚合函数。

二、ReduceFunction(增量聚合函数)

输入和输出必须一致

package com.lyh.flink07;

import com.lyh.bean.WaterSensor;
import org.apache.flink.api.common.functions.ReduceFunction;
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 Window_s_function {
    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
        env.setParallelism(1);
        env.socketTextStream("hadoop100",9999)
                .map(line -> {
                    String[] data = line.split(",");
                    return new WaterSensor(
                            data[0],
                            Long.valueOf(data[1]),
                            Integer.valueOf(data[2])
                    );
                })
                .keyBy(WaterSensor::getId)
                .window(TumblingProcessingTimeWindows.of(Time.seconds(5)))
                .reduce(new ReduceFunction<WaterSensor>() {
                    @Override
                    public WaterSensor reduce(WaterSensor value1,
                                              WaterSensor value2) throws Exception {
                        System.out.println("Window_s_function.reduce");
                        value1.setVc ( value1.getVc() + value2.getVc());
                        return (value1);
                    }
                })
                .print();

        env.execute();
    }
}

运行结果

三、AggregateFunction(增量聚合函数)

输入和输出可以不一致

package com.lyh.flink07;

import com.lyh.bean.WaterSensor;
import org.apache.flink.api.common.functions.AggregateFunction;
import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.api.functions.windowing.ProcessWindowFunction;
import org.apache.flink.streaming.api.windowing.assigners.TumblingProcessingTimeWindows;
import org.apache.flink.streaming.api.windowing.time.Time;
import org.apache.flink.streaming.api.windowing.windows.TimeWindow;
import org.apache.flink.util.Collector;
import org.apache.kafka.common.metrics.stats.Avg;

import java.util.List;

public class Window_s_function_2 {
    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
        env.setParallelism(1);
        env.socketTextStream("hadoop100",9999)
                .map(line -> {
                    String[] data = line.split(",");
                    return new WaterSensor(
                            data[0],
                            Long.valueOf(data[1]),
                            Integer.valueOf(data[2])
                    );
                })
                .keyBy(WaterSensor::getId)
                .window(TumblingProcessingTimeWindows.of(Time.seconds(5)))
                .aggregate(
                        new AggregateFunction<WaterSensor, Avg, Double>() {

                            @Override
                            public Avg createAccumulator() {
                                return new Avg();
                            }

                            @Override
                            public Avg add(WaterSensor value, Avg acc) {
                                acc.sum += value.getVc();
                                acc.couunt++;
                                return acc;

                            }

                            @Override
                            public Double getResult(Avg acc) {
                                return acc.sum * 1.0 / acc.couunt;
                            }

                            @Override
                            public Avg merge(Avg avg, Avg acc1) {
                                return null;
                            }
                        },
                        new ProcessWindowFunction<Double, String, String, TimeWindow>() {
                            @Override
                            public void process(String key,
                                                Context ctx,
                                                Iterable<Double> elements,
                                                Collector<String> out) throws Exception {
                                Double result = elements.iterator().next();
                                long starttime = ctx.window().getStart();
                                long endtime = ctx.window().getEnd();

                                out.collect("窗口：" + starttime + "  " + endtime +  " key: " + key + " result: " + result);

                            }
                        }
                )

                .print();


        env.execute();

    }
    public static class Avg {
        public Integer sum = 0;
        public Long couunt = 0L;
    };
}

运行结果

四、ProcessWindowFunction(全窗口函数)

上面例子里已经用到

new ProcessWindowFunction<Double, String, String, TimeWindow>() {
                            @Override
                            public void process(String key,
                                                Context ctx,
                                                Iterable<Double> elements,
                                                Collector<String> out) throws Exception {
                                Double result = elements.iterator().next();
                                long starttime = ctx.window().getStart();
                                long endtime = ctx.window().getEnd();

                                out.collect("窗口：" + starttime + "  " + endtime +  " key: " + key + " result: " + result);

                            }
                        }