org.apache.beam.sdk.transforms.windowing

Class WindowFn<T,W extends BoundedWindow>

java.lang.Object

org.apache.beam.sdk.transforms.windowing.WindowFn<T,W>

Type Parameters:

T - type of elements being windowed

W - BoundedWindow subclass used to represent the windows used by this WindowFn

All Implemented Interfaces:

Serializable, HasDisplayData

Direct Known Subclasses:

InvalidWindows, NonMergingWindowFn, Sessions

public abstract class WindowFn<T,W extends BoundedWindow>
extends Object
implements Serializable, HasDisplayData

The argument to the Window transform used to assign elements into windows and to determine how windows are merged. See Window for more information on how WindowFns are used and for a library of predefined WindowFns.

Users will generally want to use the predefined WindowFns, but it is also possible to create new subclasses.

To create a custom WindowFn, inherit from this class and override all required methods. If no merging is required, inherit from NonMergingWindowFn instead. If no merging is required and each element is assigned to a single window, inherit from PartitioningWindowFn. Inheriting from the most specific subclass will enable more optimizations in the runner.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	WindowFn.AssignContext Information available when running assignWindows(org.apache.beam.sdk.transforms.windowing.WindowFn<T, W>.AssignContext).
class	WindowFn.MergeContext Information available when running mergeWindows(org.apache.beam.sdk.transforms.windowing.WindowFn<T, W>.MergeContext).

Constructor Summary

Constructors

Constructor and Description
WindowFn()

Method Summary

Modifier and Type	Method and Description
abstract Collection<W>	assignWindows(WindowFn.AssignContext c) Given a timestamp and element, returns the set of windows into which it should be placed.
Instant	getOutputTime(Instant inputTimestamp, W window) Returns the output timestamp to use for data depending on the given inputTimestamp in the specified window.
abstract W	getSideInputWindow(BoundedWindow window) Returns the window of the side input corresponding to the given window of the main input.
abstract boolean	isCompatible(WindowFn<?,?> other) Returns whether this performs the same merging as the given WindowFn.
boolean	isNonMerging() Returns true if this WindowFn never needs to merge any windows.
abstract void	mergeWindows(WindowFn.MergeContext c) Does whatever merging of windows is necessary.
void	populateDisplayData(DisplayData.Builder builder) Register display data for the given transform or component.
abstract Coder<W>	windowCoder() Returns the Coder used for serializing the windows used by this windowFn.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

WindowFn

public WindowFn()

Method Detail

assignWindows

public abstract Collection<W> assignWindows(WindowFn.AssignContext c)
                                     throws Exception

Given a timestamp and element, returns the set of windows into which it should be placed.

Throws:

Exception

mergeWindows

public abstract void mergeWindows(WindowFn.MergeContext c)
                           throws Exception

Does whatever merging of windows is necessary.

See MergeOverlappingIntervalWindows.mergeWindows(org.apache.beam.sdk.transforms.windowing.WindowFn<?, org.apache.beam.sdk.transforms.windowing.IntervalWindow>.MergeContext) for an example of how to override this method.

Throws:

Exception

isCompatible

public abstract boolean isCompatible(WindowFn<?,?> other)

Returns whether this performs the same merging as the given WindowFn.

windowCoder

public abstract Coder<W> windowCoder()

Returns the Coder used for serializing the windows used by this windowFn.

getSideInputWindow

public abstract W getSideInputWindow(BoundedWindow window)

Returns the window of the side input corresponding to the given window of the main input.

Authors of custom WindowFns should override this.

getOutputTime

@Experimental(value=OUTPUT_TIME)
public Instant getOutputTime(Instant inputTimestamp,
                                                              W window)

Returns the output timestamp to use for data depending on the given inputTimestamp in the specified window.

The result of this method must be between inputTimestamp and window.maxTimestamp() (inclusive on both sides).

This function must be monotonic across input timestamps. Specifically, if A < B, then getOutputTime(A, window) <= getOutputTime(B, window).

For a WindowFn that doesn't produce overlapping windows, this can (and typically should) just return inputTimestamp. In the presence of overlapping windows, it is suggested that the result in later overlapping windows is past the end of earlier windows so that the later windows don't prevent the watermark from progressing past the end of the earlier window.

isNonMerging

public boolean isNonMerging()

Returns true if this WindowFn never needs to merge any windows.

populateDisplayData

public void populateDisplayData(DisplayData.Builder builder)

Register display data for the given transform or component.

populateDisplayData(DisplayData.Builder) is invoked by Pipeline runners to collect display data via DisplayData.from(HasDisplayData). Implementations may call super.populateDisplayData(builder) in order to register display data in the current namespace, but should otherwise use subcomponent.populateDisplayData(builder) to use the namespace of the subcomponent.

By default, does not register any display data. Implementors may override this method to provide their own display data.

Specified by:

populateDisplayData in interface HasDisplayData

Parameters:

builder - The builder to populate with display data.

See Also:

HasDisplayData