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>() {@Overridepublic 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>() {@Overridepublic Avg createAccumulator() {return new Avg();}@Overridepublic Avg add(WaterSensor value, Avg acc) {acc.sum += value.getVc();acc.couunt++;return acc;}@Overridepublic Double getResult(Avg acc) {return acc.sum * 1.0 / acc.couunt;}@Overridepublic Avg merge(Avg avg, Avg acc1) {return null;}},new ProcessWindowFunction<Double, String, String, TimeWindow>() {@Overridepublic 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>() {@Overridepublic 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);}}