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一 、 AllowedLateness API 延时关闭窗口

AllowedLateness 方法需要基于 WindowedStream 调用。AllowedLateness 需要设置一个延时时间，注意这个时间决定了窗口真正关闭的时间，而且是加上WaterMark的时间，例如 WaterMark的延时时间为2s，AllowedLateness 的时间为2s，那一个10的滚动窗口，0-10这个单位窗口正常的关窗时间应该是超过12s的数据到达之后就关窗。而AllowedLateness 是在12s的基础上继续延长了2s，也就是在14s的时候才真正去关闭 0-10s的窗口，但是在12s的时候会触发窗口计算，从12s之后到14s的数据每到达一个就会触发一次窗口计算。

二 、 OutputTag API 侧输出流

使用 OutputTag API 保证窗口关闭的数据依然可以获取，窗口到达AllowedLateness 时间后将彻底关闭，此时再属于该窗口范围内的数据将会流向 OutputTag 。

       context.collect(new Event("A", "/user", 1000L));Thread.sleep(3000);context.collect(new Event("B", "/prod", 6500L));Thread.sleep(3000);context.collect(new Event("C", "/cart", 4000L));Thread.sleep(3000);context.collect(new Event("D", "/user", 7500L));System.out.println("窗口关闭 ~ ");Thread.sleep(3000);context.collect(new Event("E", "/cente", 8500L));Thread.sleep(3000);context.collect(new Event("F", "/cente", 4000L));Thread.sleep(3000);context.collect(new Event("G", "/cente", 9200L));Thread.sleep(3000);context.collect(new Event("H", "/cente", 1000L));Thread.sleep(3000);context.collect(new Event("I", "/cente", 1500L));Thread.sleep(3000);

如果现在定义一个 5s的
滚动窗口，WaterMark延时时间为2s，AllowedLateness 延时时间为2s，此时相当于是 WaterMark到达9s的时候才会关闭0-5的窗口，也就是说最后两条数据会流向OutputTag . 当4000L数据到达后，会再次触发一次窗口计算。

完全与预期一致。

完整代码：

public class WindowOutputTest {public static void main(String[] args) throws Exception {StreamExecutionEnvironment env = Env.getEnv();DataStreamSource<Event> dataStreamSource = env.addSource(new SourceFunction<Event>() {@Overridepublic void run(SourceContext<Event> context) throws Exception {context.collect(new Event("A", "/user", 1000L));Thread.sleep(3000);context.collect(new Event("B", "/prod", 6500L));Thread.sleep(3000);context.collect(new Event("C", "/cart", 4000L));Thread.sleep(3000);context.collect(new Event("D", "/user", 7500L));System.out.println("窗口关闭 ~ ");Thread.sleep(3000);context.collect(new Event("E", "/cente", 8500L));Thread.sleep(3000);context.collect(new Event("F", "/cente", 4000L));Thread.sleep(3000);context.collect(new Event("G", "/cente", 9200L));Thread.sleep(3000);context.collect(new Event("H", "/cente", 1000L));Thread.sleep(3000);context.collect(new Event("I", "/cente", 1500L));Thread.sleep(3000);}@Overridepublic void cancel() {}});//operatorSingleOutputStreamOperator<Event> operator = dataStreamSource.assignTimestampsAndWatermarks(WatermarkStrategy.<Event>forBoundedOutOfOrderness(Duration.ofSeconds(2))// 水位线延时2s.withTimestampAssigner(new SerializableTimestampAssigner<Event>() {@Overridepublic long extractTimestamp(Event event, long l) {return event.timestamp;}}));OutputTag<Event> eventOutputTag = new OutputTag<Event>("late") {};WindowedStream<Event, Boolean, TimeWindow> windowedStream = operator.keyBy(d -> true).window(TumblingEventTimeWindows.of(Time.of(5, TimeUnit.SECONDS))).allowedLateness(Time.of(2, TimeUnit.SECONDS)).sideOutputLateData(eventOutputTag);SingleOutputStreamOperator<String> windowAgg = windowedStream.aggregate(new AggregateFunction<Event, Long, Long>() {@Overridepublic Long createAccumulator() {return 0L;}@Overridepublic Long add(Event event, Long acc) {return acc + 1;}@Overridepublic Long getResult(Long acc) {return acc;}@Overridepublic Long merge(Long aLong, Long acc1) {return null;}}, new ProcessWindowFunction<Long, String, Boolean, TimeWindow>() {@Overridepublic void process(Boolean key, Context context, Iterable<Long> iterable, Collector<String> collector) throws Exception {long start = context.window().getStart();long end = context.window().getEnd();collector.collect(new Timestamp(start) + " ~ " + new Timestamp(end) + " ===> " + iterable.iterator().next());}});windowAgg.print("窗口数据 ");//获取测输出流中的延时数据DataStream<Event> sideOutput = windowAgg.getSideOutput(eventOutputTag);sideOutput.print("测输出流：-> ");env.execute();}}