Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.beam.sdk.transforms.windowing; import com.google.auto.value.AutoValue; import javax.annotation.Nullable; import org.apache.beam.sdk.annotations.Experimental; import org.apache.beam.sdk.annotations.Experimental.Kind; import org.apache.beam.sdk.coders.Coder.NonDeterministicException; import org.apache.beam.sdk.transforms.Flatten; import org.apache.beam.sdk.transforms.GroupByKey; import org.apache.beam.sdk.transforms.MapElements; import org.apache.beam.sdk.transforms.PTransform; import org.apache.beam.sdk.transforms.SimpleFunction; import org.apache.beam.sdk.transforms.display.DisplayData; import org.apache.beam.sdk.values.PCollection; import org.apache.beam.sdk.values.PCollectionList; import org.apache.beam.sdk.values.WindowingStrategy; import org.apache.beam.sdk.values.WindowingStrategy.AccumulationMode; import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.annotations.VisibleForTesting; import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Ordering; import org.joda.time.Duration; /** * {@link Window} logically divides up or groups the elements of a {@link PCollection} into finite * windows according to a {@link WindowFn}. The output of {@code Window} contains the same elements * as input, but they have been logically assigned to windows. The next {@link * org.apache.beam.sdk.transforms.GroupByKey GroupByKeys}, including one within composite * transforms, will group by the combination of keys and windows. * * <p>See {@link org.apache.beam.sdk.transforms.GroupByKey} for more information about how grouping * with windows works. * * <h2>Windowing</h2> * * <p>Windowing a {@link PCollection} divides the elements into windows based on the associated * event time for each element. This is especially useful for {@link PCollection PCollections} with * unbounded size, since it allows operating on a sub-group of the elements placed into a related * window. For {@link PCollection PCollections} with a bounded size (aka. conventional batch mode), * by default, all data is implicitly in a single window, unless {@link Window} is applied. * * <p>For example, a simple form of windowing divides up the data into fixed-width time intervals, * using {@link FixedWindows}. The following example demonstrates how to use {@link Window} in a * pipeline that counts the number of occurrences of strings each minute: * * <pre>{@code * PCollection<String> items = ...; * PCollection<String> windowed_items = items.apply( * Window.<String>into(FixedWindows.of(Duration.standardMinutes(1)))); * PCollection<KV<String, Long>> windowed_counts = windowed_items.apply( * Count.<String>perElement()); * }</pre> * * <p>Let (data, timestamp) denote a data element along with its timestamp. Then, if the input to * this pipeline consists of {("foo", 15s), ("bar", 30s), ("foo", 45s), ("foo", 1m30s)}, the output * will be {(KV("foo", 2), 1m), (KV("bar", 1), 1m), (KV("foo", 1), 2m)} * * <p>Several predefined {@link WindowFn}s are provided: * * <ul> * <li>{@link FixedWindows} partitions the timestamps into fixed-width intervals. * <li>{@link SlidingWindows} places data into overlapping fixed-width intervals. * <li>{@link Sessions} groups data into sessions where each item in a window is separated from * the next by no more than a specified gap. * </ul> * * <p>Additionally, custom {@link WindowFn}s can be created, by creating new subclasses of {@link * WindowFn}. * * <h2>Triggers</h2> * * <p>{@link Window#triggering(Trigger)} allows specifying a trigger to control when (in processing * time) results for the given window can be produced. If unspecified, the default behavior is to * trigger first when the watermark passes the end of the window, and then trigger again every time * there is late arriving data. * * <p>Elements are added to the current window pane as they arrive. When the root trigger fires, * output is produced based on the elements in the current pane. * * <p>Depending on the trigger, this can be used both to output partial results early during the * processing of the whole window, and to deal with late arriving in batches. * * <p>Continuing the earlier example, if we wanted to emit the values that were available when the * watermark passed the end of the window, and then output any late arriving elements once-per * (actual hour) hour until we have finished processing the next 24-hours of data. (The use of * watermark time to stop processing tends to be more robust if the data source is slow for a few * days, etc.) * * <pre>{@code * PCollection<String> items = ...; * PCollection<String> windowed_items = items.apply( * Window.<String>into(FixedWindows.of(Duration.standardMinutes(1))) * .triggering( * AfterWatermark.pastEndOfWindow() * .withLateFirings(AfterProcessingTime * .pastFirstElementInPane().plusDelayOf(Duration.standardHours(1)))) * .withAllowedLateness(Duration.standardDays(1))); * PCollection<KV<String, Long>> windowed_counts = windowed_items.apply( * Count.<String>perElement()); * }</pre> * * <p>On the other hand, if we wanted to get early results every minute of processing time (for * which there were new elements in the given window) we could do the following: * * <pre>{@code * PCollection<String> windowed_items = items.apply( * Window.<String>into(FixedWindows.of(Duration.standardMinutes(1))) * .triggering( * AfterWatermark.pastEndOfWindow() * .withEarlyFirings(AfterProcessingTime * .pastFirstElementInPane().plusDelayOf(Duration.standardMinutes(1)))) * .withAllowedLateness(Duration.ZERO)); * }</pre> * * <p>After a {@link org.apache.beam.sdk.transforms.GroupByKey} the trigger is set to a trigger that * will preserve the intent of the upstream trigger. See {@link Trigger#getContinuationTrigger} for * more information. * * <p>See {@link Trigger} for details on the available triggers. */ @AutoValue public abstract class Window<T> extends PTransform<PCollection<T>, PCollection<T>> { /** * Specifies the conditions under which a final pane will be created when a window is permanently * closed. */ public enum ClosingBehavior { /** * Always fire the last pane. Even if there is no new data since the previous firing, an element * with {@link PaneInfo#isLast()} {@code true} will be produced. */ FIRE_ALWAYS, /** * Only fire the last pane if there is new data since the previous firing. * * <p>This is the default behavior. */ FIRE_IF_NON_EMPTY } /** * Specifies the conditions under which an on-time pane will be created when a window is closed. */ public enum OnTimeBehavior { /** * Always fire the on-time pane. Even if there is no new data since the previous firing, an * element will be produced. * * <p>This is the default behavior. */ FIRE_ALWAYS, /** Only fire the on-time pane if there is new data since the previous firing. */ FIRE_IF_NON_EMPTY } /** * Creates a {@code Window} {@code PTransform} that uses the given {@link WindowFn} to window the * data. * * <p>The resulting {@code PTransform}'s types have been bound, with both the input and output * being a {@code PCollection<T>}, inferred from the types of the argument {@code WindowFn}. It is * ready to be applied, or further properties can be set on it first. */ public static <T> Window<T> into(WindowFn<? super T, ?> fn) { try { fn.windowCoder().verifyDeterministic(); } catch (NonDeterministicException e) { throw new IllegalArgumentException("Window coders must be deterministic.", e); } return Window.<T>configure().withWindowFn(fn); } /** * Returns a new builder for a {@link Window} transform for setting windowing parameters other * than the windowing function. */ public static <T> Window<T> configure() { return new AutoValue_Window.Builder<T>().build(); } @Nullable public abstract WindowFn<? super T, ?> getWindowFn(); @Nullable abstract Trigger getTrigger(); @Nullable abstract AccumulationMode getAccumulationMode(); @Nullable abstract Duration getAllowedLateness(); @Nullable abstract ClosingBehavior getClosingBehavior(); @Nullable abstract OnTimeBehavior getOnTimeBehavior(); @Nullable abstract TimestampCombiner getTimestampCombiner(); abstract Builder<T> toBuilder(); @AutoValue.Builder abstract static class Builder<T> { abstract Builder<T> setWindowFn(WindowFn<? super T, ?> windowFn); abstract Builder<T> setTrigger(Trigger trigger); abstract Builder<T> setAccumulationMode(AccumulationMode mode); abstract Builder<T> setAllowedLateness(Duration allowedLateness); abstract Builder<T> setClosingBehavior(ClosingBehavior closingBehavior); abstract Builder<T> setOnTimeBehavior(OnTimeBehavior onTimeBehavior); abstract Builder<T> setTimestampCombiner(TimestampCombiner timestampCombiner); abstract Window<T> build(); } private Window<T> withWindowFn(WindowFn<? super T, ?> windowFn) { return toBuilder().setWindowFn(windowFn).build(); } /** * Sets a non-default trigger for this {@code Window} {@code PTransform}. Elements that are * assigned to a specific window will be output when the trigger fires. * * <p>{@link org.apache.beam.sdk.transforms.windowing.Trigger} has more details on the available * triggers. * * <p>Must also specify allowed lateness using {@link #withAllowedLateness} and accumulation mode * using either {@link #discardingFiredPanes()} or {@link #accumulatingFiredPanes()}. */ @Experimental(Kind.TRIGGER) public Window<T> triggering(Trigger trigger) { return toBuilder().setTrigger(trigger).build(); } /** * Returns a new {@code Window} {@code PTransform} that uses the registered WindowFn and * Triggering behavior, and that discards elements in a pane after they are triggered. * * <p>Does not modify this transform. The resulting {@code PTransform} is sufficiently specified * to be applied, but more properties can still be specified. */ @Experimental(Kind.TRIGGER) public Window<T> discardingFiredPanes() { return toBuilder().setAccumulationMode(AccumulationMode.DISCARDING_FIRED_PANES).build(); } /** * Returns a new {@code Window} {@code PTransform} that uses the registered WindowFn and * Triggering behavior, and that accumulates elements in a pane after they are triggered. * * <p>Does not modify this transform. The resulting {@code PTransform} is sufficiently specified * to be applied, but more properties can still be specified. */ @Experimental(Kind.TRIGGER) public Window<T> accumulatingFiredPanes() { return toBuilder().setAccumulationMode(AccumulationMode.ACCUMULATING_FIRED_PANES).build(); } /** * Override the amount of lateness allowed for data elements in the output {@link PCollection} and * downstream {@link PCollection PCollections} until explicitly set again. Like the other * properties on this {@link Window} operation, this will be applied at the next {@link * GroupByKey}. Any elements that are later than this as decided by the system-maintained * watermark will be dropped. * * <p>This value also determines how long state will be kept around for old windows. Once no * elements will be added to a window (because this duration has passed) any state associated with * the window will be cleaned up. * * <p>Depending on the trigger this may not produce a pane with {@link PaneInfo#isLast}. See * {@link ClosingBehavior#FIRE_IF_NON_EMPTY} for more details. */ @Experimental(Kind.TRIGGER) public Window<T> withAllowedLateness(Duration allowedLateness) { return toBuilder().setAllowedLateness(allowedLateness).build(); } /** * <b><i>(Experimental)</i></b> Override the default {@link TimestampCombiner}, to control the * output timestamp of values output from a {@link GroupByKey} operation. */ @Experimental(Kind.OUTPUT_TIME) public Window<T> withTimestampCombiner(TimestampCombiner timestampCombiner) { return toBuilder().setTimestampCombiner(timestampCombiner).build(); } /** * Override the amount of lateness allowed for data elements in the pipeline. Like the other * properties on this {@link Window} operation, this will be applied at the next {@link * GroupByKey}. Any elements that are later than this as decided by the system-maintained * watermark will be dropped. * * <p>This value also determines how long state will be kept around for old windows. Once no * elements will be added to a window (because this duration has passed) any state associated with * the window will be cleaned up. */ @Experimental(Kind.TRIGGER) public Window<T> withAllowedLateness(Duration allowedLateness, ClosingBehavior behavior) { return toBuilder().setAllowedLateness(allowedLateness).setClosingBehavior(behavior).build(); } /** * <b><i>(Experimental)</i></b> Override the default {@link OnTimeBehavior}, to control whether to * output an empty on-time pane. */ @Experimental(Kind.TRIGGER) public Window<T> withOnTimeBehavior(OnTimeBehavior behavior) { return toBuilder().setOnTimeBehavior(behavior).build(); } /** Get the output strategy of this {@link Window Window PTransform}. For internal use only. */ public WindowingStrategy<?, ?> getOutputStrategyInternal(WindowingStrategy<?, ?> inputStrategy) { WindowingStrategy<?, ?> result = inputStrategy; if (getWindowFn() != null) { result = result.withWindowFn(getWindowFn()); } if (getTrigger() != null) { result = result.withTrigger(getTrigger()); } if (getAccumulationMode() != null) { result = result.withMode(getAccumulationMode()); } if (getAllowedLateness() != null) { result = result.withAllowedLateness( Ordering.natural().max(getAllowedLateness(), inputStrategy.getAllowedLateness())); } if (getClosingBehavior() != null) { result = result.withClosingBehavior(getClosingBehavior()); } if (getOnTimeBehavior() != null) { result = result.withOnTimeBehavior(getOnTimeBehavior()); } if (getTimestampCombiner() != null) { result = result.withTimestampCombiner(getTimestampCombiner()); } return result; } private void applicableTo(PCollection<?> input) { WindowingStrategy<?, ?> outputStrategy = getOutputStrategyInternal(input.getWindowingStrategy()); // Make sure that the windowing strategy is complete & valid. if (outputStrategy.isTriggerSpecified() && !(outputStrategy.getTrigger() instanceof DefaultTrigger) && !(outputStrategy.getWindowFn() instanceof GlobalWindows) && !outputStrategy.isAllowedLatenessSpecified()) { throw new IllegalArgumentException("Except when using GlobalWindows," + " calling .triggering() to specify a trigger requires that the allowed lateness" + " be specified using .withAllowedLateness() to set the upper bound on how late" + " data can arrive before being dropped. See Javadoc for more details."); } if (!outputStrategy.isModeSpecified() && canProduceMultiplePanes(outputStrategy)) { throw new IllegalArgumentException( "Calling .triggering() to specify a trigger or calling .withAllowedLateness() to" + " specify an allowed lateness greater than zero requires that the accumulation" + " mode be specified using .discardingFiredPanes() or .accumulatingFiredPanes()." + " See Javadoc for more details."); } } private boolean canProduceMultiplePanes(WindowingStrategy<?, ?> strategy) { // The default trigger is Repeatedly.forever(AfterWatermark.pastEndOfWindow()); This fires // for every late-arriving element if allowed lateness is nonzero, and thus we must have // an accumulating mode specified boolean dataCanArriveLate = !(strategy.getWindowFn() instanceof GlobalWindows) && strategy.getAllowedLateness().getMillis() > 0; boolean hasCustomTrigger = !(strategy.getTrigger() instanceof DefaultTrigger); return dataCanArriveLate || hasCustomTrigger; } @Override public PCollection<T> expand(PCollection<T> input) { applicableTo(input); WindowingStrategy<?, ?> outputStrategy = getOutputStrategyInternal(input.getWindowingStrategy()); if (getWindowFn() == null) { // A new PCollection must be created in case input is reused in a different location as the // two PCollections will, in general, have a different windowing strategy. return PCollectionList.of(input).apply(Flatten.pCollections()) .setWindowingStrategyInternal(outputStrategy); } else { // This is the AssignWindows primitive return input.apply(new Assign<>(this, outputStrategy)); } } @Override public void populateDisplayData(DisplayData.Builder builder) { super.populateDisplayData(builder); if (getWindowFn() != null) { builder.add(DisplayData.item("windowFn", getWindowFn().getClass()).withLabel("Windowing Function")) .include("windowFn", getWindowFn()); } if (getAllowedLateness() != null) { builder.addIfNotDefault( DisplayData.item("allowedLateness", getAllowedLateness()).withLabel("Allowed Lateness"), Duration.millis(BoundedWindow.TIMESTAMP_MAX_VALUE.getMillis())); } if (getTrigger() != null && !(getTrigger() instanceof DefaultTrigger)) { builder.add(DisplayData.item("trigger", getTrigger().toString()).withLabel("Trigger")); } if (getAccumulationMode() != null) { builder.add(DisplayData.item("accumulationMode", getAccumulationMode().toString()) .withLabel("Accumulation Mode")); } if (getClosingBehavior() != null) { builder.add(DisplayData.item("closingBehavior", getClosingBehavior().toString()) .withLabel("Window Closing Behavior")); } if (getTimestampCombiner() != null) { builder.add(DisplayData.item("timestampCombiner", getTimestampCombiner().toString()) .withLabel("Timestamp Combiner")); } } @Override protected String getKindString() { return "Window.Into()"; } /** * A Primitive {@link PTransform} that assigns windows to elements based on a {@link WindowFn}. * Pipeline authors should use {@link Window} directly instead. */ public static class Assign<T> extends PTransform<PCollection<T>, PCollection<T>> { private final Window<T> original; private final WindowingStrategy<T, ?> updatedStrategy; /** * Create a new {@link Assign} where the output is windowed with the updated {@link * WindowingStrategy}. Windows should be assigned using the {@link WindowFn} returned by {@link * #getWindowFn()}. */ @VisibleForTesting Assign(Window<T> original, WindowingStrategy updatedStrategy) { this.original = original; this.updatedStrategy = updatedStrategy; } @Override public PCollection<T> expand(PCollection<T> input) { return PCollection.createPrimitiveOutputInternal(input.getPipeline(), updatedStrategy, input.isBounded(), input.getCoder()); } @Override public void populateDisplayData(DisplayData.Builder builder) { original.populateDisplayData(builder); } @Nullable public WindowFn<T, ?> getWindowFn() { return updatedStrategy.getWindowFn(); } } /** * Creates a {@code Window} {@code PTransform} that does not change assigned windows, but will * cause windows to be merged again as part of the next {@link * org.apache.beam.sdk.transforms.GroupByKey}. */ public static <T> Remerge<T> remerge() { return new Remerge<>(); } /** * {@code PTransform} that does not change assigned windows, but will cause windows to be merged * again as part of the next {@link org.apache.beam.sdk.transforms.GroupByKey}. */ private static class Remerge<T> extends PTransform<PCollection<T>, PCollection<T>> { @Override public PCollection<T> expand(PCollection<T> input) { WindowingStrategy<?, ?> outputWindowingStrategy = getOutputWindowing(input.getWindowingStrategy()); return input // We first apply a (trivial) transform to the input PCollection to produce a new // PCollection. This ensures that we don't modify the windowing strategy of the input // which may be used elsewhere. .apply("Identity", MapElements.via(new SimpleFunction<T, T>() { @Override public T apply(T element) { return element; } })) // Then we modify the windowing strategy. .setWindowingStrategyInternal(outputWindowingStrategy); } private <W extends BoundedWindow> WindowingStrategy<?, W> getOutputWindowing( WindowingStrategy<?, W> inputStrategy) { if (inputStrategy.getWindowFn() instanceof InvalidWindows) { @SuppressWarnings("unchecked") InvalidWindows<W> invalidWindows = (InvalidWindows<W>) inputStrategy.getWindowFn(); return inputStrategy.withWindowFn(invalidWindows.getOriginalWindowFn()); } else { return inputStrategy; } } } }