Flink 窗口触发器(Trigger)(一)

Flink 窗口触发器(Trigger)(一)
Flink 窗口触发器(Trigger)(二)

Flink的窗口触发器（Trigger）是流处理中一个非常关键的概念，它定义了窗口何时被触发并决定触发后的行为（如进行窗口数据的计算或清理）。

一、基本概念

  • 定义：触发器决定了窗口何时被触发以及触发后的行为。在Flink中，窗口的触发是通过设置定时器来实现的。
  • 作用：控制窗口数据的聚合时机，确保数据在适当的时间点被处理和输出。
    在这里插入图片描述

二、类型

Flink提供了多种内置的触发器，以下几种为常用类型：

  1. EventTimeTrigger
  • 工作原理：基于事件时间和水印（Watermark）机制来触发窗口计算。当窗口的最大时间戳小于等于当前的水印时，立即触发窗口计算。
  • 适用场景：适用于需要基于事件时间进行处理的场景，如金融交易、日志分析等。
  1. ProcessingTimeTrigger
  • 工作原理：基于处理时间（即机器的系统时间）来触发窗口计算。当处理时间达到窗口的结束时间时，触发窗口计算。
  • 适用场景：适用于对时间精度要求不高的场景，或者当事件时间无法准确获取时。
  1. CountTrigger
  • 工作原理：根据窗口内元素的数量来触发计算。当窗口内的元素数量达到预设的阈值时，触发窗口计算。
  • 适用场景：适用于需要基于数据量进行处理的场景，如批量数据处理、流量分析等。
  1. ContinuousEventTimeTrigger和ContinuousProcessingTimeTrigger
  • 工作原理：根据间隔时间周期性触发窗口计算，或者当窗口的结束时间小于当前的时间（事件时间或处理时间）时触发计算。
  • 适用场景：适用于需要周期性处理数据的场景，如实时监控、周期性报表等。
  1. DeltaTrigger
  • 工作原理：根据接入数据计算出的Delta指标是否超过指定的阈值来触发窗口计算。
  • 适用场景：适用于需要基于数据变化量进行处理的场景，如异常检测、趋势分析等。
  1. PurgingTrigger
  • 工作原理：将其他触发器作为参数转换为Purge类型的触发器，在触发计算后清除窗口内的数据。
  • 适用场景：适用于需要在计算完成后立即清除窗口数据的场景，以节省存储空间。

三、关键方法

触发器通常包含以下几个关键方法：

  1. onElement(T element, long timestamp, W window, TriggerContext ctx)
    当元素被添加到窗口时调用，用于注册定时器或更新窗口状态。
  2. onEventTime(long time, W window, TriggerContext ctx)
    当事件时间计时器触发时调用，用于处理事件时间相关的触发逻辑。
  3. onProcessingTime(long time, W window, TriggerContext ctx)
    当处理时间计时器触发时调用，用于处理处理时间相关的触发逻辑。
  4. onMerge(W window, OnMergeContext ctx)（可选）
    当两个窗口合并时调用，用于合并窗口的状态和定时器。
  5. clear(W window, TriggerContext ctx)
    当窗口被删除时调用，用于清理窗口的状态和定时器。

四、行为

触发器在触发时会返回一个TriggerResult枚举值，以决定窗口的后续行为。常见的TriggerResult值包括：

  • CONTINUE：表示不进行任何操作，等待下一个触发条件。
  • FIRE：表示触发窗口计算并输出结果，但窗口状态保持不变。
  • PURGE：表示不触发窗口计算，只清除窗口内的数据和状态。
  • FIRE_AND_PURGE：表示触发窗口计算并输出结果，然后清除窗口内的数据和状态。

Flink的窗口触发器是流处理中非常灵活且强大的工具，它允许开发者根据实际需求定义窗口的触发条件和触发后的行为。通过选择合适的触发器和配置相应的参数，可以实现高效、准确的流数据处理。

五、Trigger

EventTimeTrigger

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.apache.flink.streaming.api.windowing.triggers;import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.streaming.api.windowing.windows.TimeWindow;@PublicEvolving
public class EventTimeTrigger extends Trigger<Object, TimeWindow> {private static final long serialVersionUID = 1L;private EventTimeTrigger() {}public TriggerResult onElement(Object element, long timestamp, TimeWindow window, Trigger.TriggerContext ctx) throws Exception {if (window.maxTimestamp() <= ctx.getCurrentWatermark()) {return TriggerResult.FIRE;} else {ctx.registerEventTimeTimer(window.maxTimestamp());return TriggerResult.CONTINUE;}}public TriggerResult onEventTime(long time, TimeWindow window, Trigger.TriggerContext ctx) {return time == window.maxTimestamp() ? TriggerResult.FIRE : TriggerResult.CONTINUE;}public TriggerResult onProcessingTime(long time, TimeWindow window, Trigger.TriggerContext ctx) throws Exception {return TriggerResult.CONTINUE;}public void clear(TimeWindow window, Trigger.TriggerContext ctx) throws Exception {ctx.deleteEventTimeTimer(window.maxTimestamp());}public boolean canMerge() {return true;}public void onMerge(TimeWindow window, Trigger.OnMergeContext ctx) {long windowMaxTimestamp = window.maxTimestamp();if (windowMaxTimestamp > ctx.getCurrentWatermark()) {ctx.registerEventTimeTimer(windowMaxTimestamp);}}public String toString() {return "EventTimeTrigger()";}public static EventTimeTrigger create() {return new EventTimeTrigger();}
}

ProcessingTimeTrigger

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.apache.flink.streaming.api.windowing.triggers;import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.streaming.api.windowing.windows.TimeWindow;@PublicEvolving
public class ProcessingTimeTrigger extends Trigger<Object, TimeWindow> {private static final long serialVersionUID = 1L;private ProcessingTimeTrigger() {}public TriggerResult onElement(Object element, long timestamp, TimeWindow window, Trigger.TriggerContext ctx) {ctx.registerProcessingTimeTimer(window.maxTimestamp());return TriggerResult.CONTINUE;}public TriggerResult onEventTime(long time, TimeWindow window, Trigger.TriggerContext ctx) throws Exception {return TriggerResult.CONTINUE;}public TriggerResult onProcessingTime(long time, TimeWindow window, Trigger.TriggerContext ctx) {return TriggerResult.FIRE;}public void clear(TimeWindow window, Trigger.TriggerContext ctx) throws Exception {ctx.deleteProcessingTimeTimer(window.maxTimestamp());}public boolean canMerge() {return true;}public void onMerge(TimeWindow window, Trigger.OnMergeContext ctx) {long windowMaxTimestamp = window.maxTimestamp();if (windowMaxTimestamp > ctx.getCurrentProcessingTime()) {ctx.registerProcessingTimeTimer(windowMaxTimestamp);}}public String toString() {return "ProcessingTimeTrigger()";}public static ProcessingTimeTrigger create() {return new ProcessingTimeTrigger();}
}

ProcessingTimeoutTrigger

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.apache.flink.streaming.api.windowing.triggers;import java.time.Duration;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.state.ValueState;
import org.apache.flink.api.common.state.ValueStateDescriptor;
import org.apache.flink.api.common.typeutils.base.LongSerializer;
import org.apache.flink.streaming.api.windowing.windows.Window;@PublicEvolving
public class ProcessingTimeoutTrigger<T, W extends Window> extends Trigger<T, W> {private static final long serialVersionUID = 1L;private final Trigger<T, W> nestedTrigger;private final long interval;private final boolean resetTimerOnNewRecord;private final boolean shouldClearOnTimeout;private final ValueStateDescriptor<Long> timeoutStateDesc;private ProcessingTimeoutTrigger(Trigger<T, W> nestedTrigger, long interval, boolean resetTimerOnNewRecord, boolean shouldClearOnTimeout) {this.nestedTrigger = nestedTrigger;this.interval = interval;this.resetTimerOnNewRecord = resetTimerOnNewRecord;this.shouldClearOnTimeout = shouldClearOnTimeout;this.timeoutStateDesc = new ValueStateDescriptor("timeout", LongSerializer.INSTANCE);}public TriggerResult onElement(T element, long timestamp, W window, Trigger.TriggerContext ctx) throws Exception {TriggerResult triggerResult = this.nestedTrigger.onElement(element, timestamp, window, ctx);if (triggerResult.isFire()) {this.clear(window, ctx);return triggerResult;} else {ValueState<Long> timeoutState = (ValueState)ctx.getPartitionedState(this.timeoutStateDesc);long nextFireTimestamp = ctx.getCurrentProcessingTime() + this.interval;Long timeoutTimestamp = (Long)timeoutState.value();if (timeoutTimestamp != null && this.resetTimerOnNewRecord) {ctx.deleteProcessingTimeTimer(timeoutTimestamp);timeoutState.clear();timeoutTimestamp = null;}if (timeoutTimestamp == null) {timeoutState.update(nextFireTimestamp);ctx.registerProcessingTimeTimer(nextFireTimestamp);}return triggerResult;}}public TriggerResult onProcessingTime(long timestamp, W window, Trigger.TriggerContext ctx) throws Exception {TriggerResult triggerResult = this.nestedTrigger.onProcessingTime(timestamp, window, ctx);if (this.shouldClearOnTimeout) {this.clear(window, ctx);}return triggerResult.isPurge() ? TriggerResult.FIRE_AND_PURGE : TriggerResult.FIRE;}public TriggerResult onEventTime(long timestamp, W window, Trigger.TriggerContext ctx) throws Exception {TriggerResult triggerResult = this.nestedTrigger.onEventTime(timestamp, window, ctx);if (this.shouldClearOnTimeout) {this.clear(window, ctx);}return triggerResult.isPurge() ? TriggerResult.FIRE_AND_PURGE : TriggerResult.FIRE;}public void clear(W window, Trigger.TriggerContext ctx) throws Exception {ValueState<Long> timeoutTimestampState = (ValueState)ctx.getPartitionedState(this.timeoutStateDesc);Long timeoutTimestamp = (Long)timeoutTimestampState.value();if (timeoutTimestamp != null) {ctx.deleteProcessingTimeTimer(timeoutTimestamp);timeoutTimestampState.clear();}this.nestedTrigger.clear(window, ctx);}public String toString() {return "TimeoutTrigger(" + this.nestedTrigger.toString() + ")";}public static <T, W extends Window> ProcessingTimeoutTrigger<T, W> of(Trigger<T, W> nestedTrigger, Duration timeout) {return new ProcessingTimeoutTrigger(nestedTrigger, timeout.toMillis(), false, true);}public static <T, W extends Window> ProcessingTimeoutTrigger<T, W> of(Trigger<T, W> nestedTrigger, Duration timeout, boolean resetTimerOnNewRecord, boolean shouldClearOnTimeout) {return new ProcessingTimeoutTrigger(nestedTrigger, timeout.toMillis(), resetTimerOnNewRecord, shouldClearOnTimeout);}
}

CountTrigger

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.apache.flink.streaming.api.windowing.triggers;import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.common.state.ReducingState;
import org.apache.flink.api.common.state.ReducingStateDescriptor;
import org.apache.flink.api.common.typeutils.base.LongSerializer;
import org.apache.flink.streaming.api.windowing.windows.Window;@PublicEvolving
public class CountTrigger<W extends Window> extends Trigger<Object, W> {private static final long serialVersionUID = 1L;private final long maxCount;private final ReducingStateDescriptor<Long> stateDesc;private CountTrigger(long maxCount) {this.stateDesc = new ReducingStateDescriptor("count", new Sum(), LongSerializer.INSTANCE);this.maxCount = maxCount;}public TriggerResult onElement(Object element, long timestamp, W window, Trigger.TriggerContext ctx) throws Exception {ReducingState<Long> count = (ReducingState)ctx.getPartitionedState(this.stateDesc);count.add(1L);if ((Long)count.get() >= this.maxCount) {count.clear();return TriggerResult.FIRE;} else {return TriggerResult.CONTINUE;}}public TriggerResult onEventTime(long time, W window, Trigger.TriggerContext ctx) {return TriggerResult.CONTINUE;}public TriggerResult onProcessingTime(long time, W window, Trigger.TriggerContext ctx) throws Exception {return TriggerResult.CONTINUE;}public void clear(W window, Trigger.TriggerContext ctx) throws Exception {((ReducingState)ctx.getPartitionedState(this.stateDesc)).clear();}public boolean canMerge() {return true;}public void onMerge(W window, Trigger.OnMergeContext ctx) throws Exception {ctx.mergePartitionedState(this.stateDesc);}public String toString() {return "CountTrigger(" + this.maxCount + ")";}public static <W extends Window> CountTrigger<W> of(long maxCount) {return new CountTrigger(maxCount);}private static class Sum implements ReduceFunction<Long> {private static final long serialVersionUID = 1L;private Sum() {}public Long reduce(Long value1, Long value2) throws Exception {return value1 + value2;}}
}

ContinuousEventTimeTrigger和ContinuousProcessingTimeTrigger

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.apache.flink.streaming.api.windowing.triggers;import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.annotation.VisibleForTesting;
import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.common.state.ReducingState;
import org.apache.flink.api.common.state.ReducingStateDescriptor;
import org.apache.flink.api.common.typeutils.base.LongSerializer;
import org.apache.flink.streaming.api.windowing.time.Time;
import org.apache.flink.streaming.api.windowing.windows.Window;@PublicEvolving
public class ContinuousEventTimeTrigger<W extends Window> extends Trigger<Object, W> {private static final long serialVersionUID = 1L;private final long interval;private final ReducingStateDescriptor<Long> stateDesc;private ContinuousEventTimeTrigger(long interval) {this.stateDesc = new ReducingStateDescriptor("fire-time", new Min(), LongSerializer.INSTANCE);this.interval = interval;}public TriggerResult onElement(Object element, long timestamp, W window, Trigger.TriggerContext ctx) throws Exception {if (window.maxTimestamp() <= ctx.getCurrentWatermark()) {return TriggerResult.FIRE;} else {ctx.registerEventTimeTimer(window.maxTimestamp());ReducingState<Long> fireTimestampState = (ReducingState)ctx.getPartitionedState(this.stateDesc);if (fireTimestampState.get() == null) {this.registerNextFireTimestamp(timestamp - timestamp % this.interval, window, ctx, fireTimestampState);}return TriggerResult.CONTINUE;}}public TriggerResult onEventTime(long time, W window, Trigger.TriggerContext ctx) throws Exception {if (time == window.maxTimestamp()) {return TriggerResult.FIRE;} else {ReducingState<Long> fireTimestampState = (ReducingState)ctx.getPartitionedState(this.stateDesc);Long fireTimestamp = (Long)fireTimestampState.get();if (fireTimestamp != null && fireTimestamp == time) {fireTimestampState.clear();this.registerNextFireTimestamp(time, window, ctx, fireTimestampState);return TriggerResult.FIRE;} else {return TriggerResult.CONTINUE;}}}public TriggerResult onProcessingTime(long time, W window, Trigger.TriggerContext ctx) throws Exception {return TriggerResult.CONTINUE;}public void clear(W window, Trigger.TriggerContext ctx) throws Exception {ReducingState<Long> fireTimestamp = (ReducingState)ctx.getPartitionedState(this.stateDesc);Long timestamp = (Long)fireTimestamp.get();if (timestamp != null) {ctx.deleteEventTimeTimer(timestamp);fireTimestamp.clear();}}public boolean canMerge() {return true;}public void onMerge(W window, Trigger.OnMergeContext ctx) throws Exception {ctx.mergePartitionedState(this.stateDesc);Long nextFireTimestamp = (Long)((ReducingState)ctx.getPartitionedState(this.stateDesc)).get();if (nextFireTimestamp != null) {ctx.registerEventTimeTimer(nextFireTimestamp);}}public String toString() {return "ContinuousEventTimeTrigger(" + this.interval + ")";}@VisibleForTestingpublic long getInterval() {return this.interval;}public static <W extends Window> ContinuousEventTimeTrigger<W> of(Time interval) {return new ContinuousEventTimeTrigger(interval.toMilliseconds());}private void registerNextFireTimestamp(long time, W window, Trigger.TriggerContext ctx, ReducingState<Long> fireTimestampState) throws Exception {long nextFireTimestamp = Math.min(time + this.interval, window.maxTimestamp());fireTimestampState.add(nextFireTimestamp);ctx.registerEventTimeTimer(nextFireTimestamp);}private static class Min implements ReduceFunction<Long> {private static final long serialVersionUID = 1L;private Min() {}public Long reduce(Long value1, Long value2) throws Exception {return Math.min(value1, value2);}}
}
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.apache.flink.streaming.api.windowing.triggers;import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.annotation.VisibleForTesting;
import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.common.state.ReducingState;
import org.apache.flink.api.common.state.ReducingStateDescriptor;
import org.apache.flink.api.common.typeutils.base.LongSerializer;
import org.apache.flink.streaming.api.windowing.time.Time;
import org.apache.flink.streaming.api.windowing.windows.Window;@PublicEvolving
public class ContinuousProcessingTimeTrigger<W extends Window> extends Trigger<Object, W> {private static final long serialVersionUID = 1L;private final long interval;private final ReducingStateDescriptor<Long> stateDesc;private ContinuousProcessingTimeTrigger(long interval) {this.stateDesc = new ReducingStateDescriptor("fire-time", new Min(), LongSerializer.INSTANCE);this.interval = interval;}public TriggerResult onElement(Object element, long timestamp, W window, Trigger.TriggerContext ctx) throws Exception {ReducingState<Long> fireTimestampState = (ReducingState)ctx.getPartitionedState(this.stateDesc);timestamp = ctx.getCurrentProcessingTime();if (fireTimestampState.get() == null) {this.registerNextFireTimestamp(timestamp - timestamp % this.interval, window, ctx, fireTimestampState);}return TriggerResult.CONTINUE;}public TriggerResult onEventTime(long time, W window, Trigger.TriggerContext ctx) throws Exception {return TriggerResult.CONTINUE;}public TriggerResult onProcessingTime(long time, W window, Trigger.TriggerContext ctx) throws Exception {ReducingState<Long> fireTimestampState = (ReducingState)ctx.getPartitionedState(this.stateDesc);if (((Long)fireTimestampState.get()).equals(time)) {fireTimestampState.clear();this.registerNextFireTimestamp(time, window, ctx, fireTimestampState);return TriggerResult.FIRE;} else {return TriggerResult.CONTINUE;}}public void clear(W window, Trigger.TriggerContext ctx) throws Exception {ReducingState<Long> fireTimestamp = (ReducingState)ctx.getPartitionedState(this.stateDesc);Long timestamp = (Long)fireTimestamp.get();if (timestamp != null) {ctx.deleteProcessingTimeTimer(timestamp);fireTimestamp.clear();}}public boolean canMerge() {return true;}public void onMerge(W window, Trigger.OnMergeContext ctx) throws Exception {ctx.mergePartitionedState(this.stateDesc);Long nextFireTimestamp = (Long)((ReducingState)ctx.getPartitionedState(this.stateDesc)).get();if (nextFireTimestamp != null) {ctx.registerProcessingTimeTimer(nextFireTimestamp);}}@VisibleForTestingpublic long getInterval() {return this.interval;}public String toString() {return "ContinuousProcessingTimeTrigger(" + this.interval + ")";}public static <W extends Window> ContinuousProcessingTimeTrigger<W> of(Time interval) {return new ContinuousProcessingTimeTrigger(interval.toMilliseconds());}private void registerNextFireTimestamp(long time, W window, Trigger.TriggerContext ctx, ReducingState<Long> fireTimestampState) throws Exception {long nextFireTimestamp = Math.min(time + this.interval, window.maxTimestamp());fireTimestampState.add(nextFireTimestamp);ctx.registerProcessingTimeTimer(nextFireTimestamp);}private static class Min implements ReduceFunction<Long> {private static final long serialVersionUID = 1L;private Min() {}public Long reduce(Long value1, Long value2) throws Exception {return Math.min(value1, value2);}}
}

DeltaTrigger

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.apache.flink.streaming.api.windowing.triggers;import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.state.ValueState;
import org.apache.flink.api.common.state.ValueStateDescriptor;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.streaming.api.functions.windowing.delta.DeltaFunction;
import org.apache.flink.streaming.api.windowing.windows.Window;@PublicEvolving
public class DeltaTrigger<T, W extends Window> extends Trigger<T, W> {private static final long serialVersionUID = 1L;private final DeltaFunction<T> deltaFunction;private final double threshold;private final ValueStateDescriptor<T> stateDesc;private DeltaTrigger(double threshold, DeltaFunction<T> deltaFunction, TypeSerializer<T> stateSerializer) {this.deltaFunction = deltaFunction;this.threshold = threshold;this.stateDesc = new ValueStateDescriptor("last-element", stateSerializer);}public TriggerResult onElement(T element, long timestamp, W window, Trigger.TriggerContext ctx) throws Exception {ValueState<T> lastElementState = (ValueState)ctx.getPartitionedState(this.stateDesc);if (lastElementState.value() == null) {lastElementState.update(element);return TriggerResult.CONTINUE;} else if (this.deltaFunction.getDelta(lastElementState.value(), element) > this.threshold) {lastElementState.update(element);return TriggerResult.FIRE;} else {return TriggerResult.CONTINUE;}}public TriggerResult onEventTime(long time, W window, Trigger.TriggerContext ctx) {return TriggerResult.CONTINUE;}public TriggerResult onProcessingTime(long time, W window, Trigger.TriggerContext ctx) throws Exception {return TriggerResult.CONTINUE;}public void clear(W window, Trigger.TriggerContext ctx) throws Exception {((ValueState)ctx.getPartitionedState(this.stateDesc)).clear();}public String toString() {return "DeltaTrigger(" + this.deltaFunction + ", " + this.threshold + ")";}public static <T, W extends Window> DeltaTrigger<T, W> of(double threshold, DeltaFunction<T> deltaFunction, TypeSerializer<T> stateSerializer) {return new DeltaTrigger(threshold, deltaFunction, stateSerializer);}
}

PurgingTrigger

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.apache.flink.streaming.api.windowing.triggers;import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.annotation.VisibleForTesting;
import org.apache.flink.streaming.api.windowing.windows.Window;@PublicEvolving
public class PurgingTrigger<T, W extends Window> extends Trigger<T, W> {private static final long serialVersionUID = 1L;private Trigger<T, W> nestedTrigger;private PurgingTrigger(Trigger<T, W> nestedTrigger) {this.nestedTrigger = nestedTrigger;}public TriggerResult onElement(T element, long timestamp, W window, Trigger.TriggerContext ctx) throws Exception {TriggerResult triggerResult = this.nestedTrigger.onElement(element, timestamp, window, ctx);return triggerResult.isFire() ? TriggerResult.FIRE_AND_PURGE : triggerResult;}public TriggerResult onEventTime(long time, W window, Trigger.TriggerContext ctx) throws Exception {TriggerResult triggerResult = this.nestedTrigger.onEventTime(time, window, ctx);return triggerResult.isFire() ? TriggerResult.FIRE_AND_PURGE : triggerResult;}public TriggerResult onProcessingTime(long time, W window, Trigger.TriggerContext ctx) throws Exception {TriggerResult triggerResult = this.nestedTrigger.onProcessingTime(time, window, ctx);return triggerResult.isFire() ? TriggerResult.FIRE_AND_PURGE : triggerResult;}public void clear(W window, Trigger.TriggerContext ctx) throws Exception {this.nestedTrigger.clear(window, ctx);}public boolean canMerge() {return this.nestedTrigger.canMerge();}public void onMerge(W window, Trigger.OnMergeContext ctx) throws Exception {this.nestedTrigger.onMerge(window, ctx);}public String toString() {return "PurgingTrigger(" + this.nestedTrigger.toString() + ")";}public static <T, W extends Window> PurgingTrigger<T, W> of(Trigger<T, W> nestedTrigger) {return new PurgingTrigger(nestedTrigger);}@VisibleForTestingpublic Trigger<T, W> getNestedTrigger() {return this.nestedTrigger;}
}

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