com.google.cloud.dataflow.sdk.transforms.windowing

Class WindowFn<T,W extends BoundedWindow>

java.lang.Object

com.google.cloud.dataflow.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

Direct Known Subclasses:

InvalidWindows, NonMergingWindowFn, Sessions

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

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. TODO: Describe how to properly create WindowFns.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	WindowFn.AssignContext Information available when running assignWindows(com.google.cloud.dataflow.sdk.transforms.windowing.WindowFn<T, W>.AssignContext).
class	WindowFn.MergeContext Information available when running mergeWindows(com.google.cloud.dataflow.sdk.transforms.windowing.WindowFn<T, W>.MergeContext).

Constructor Summary

Constructors

Constructor and Description
WindowFn()

Method Summary

Modifier and Type	Method and Description
boolean	assignsToSingleWindow() Returns true if this WindowFn assigns each element to a single window.
abstract Collection<W>	assignWindows(WindowFn.AssignContext c) Given a timestamp and element, returns the set of windows into which it should be placed.
abstract org.joda.time.Instant	getOutputTime(org.joda.time.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.
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(com.google.cloud.dataflow.sdk.transforms.windowing.WindowFn<?, com.google.cloud.dataflow.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

public abstract org.joda.time.Instant getOutputTime(org.joda.time.Instant inputTimestamp,
                                                    W window)

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

The result must be between inputTimestamp and window.maxTimestamp() (inclusive on both sides). If this WindowFn doesn't produce overlapping windows, this can (and typically should) just return inputTimestamp. If this does produce 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.

Each KV<K, Iterable<V>> produced from a GroupByKey will be output at a timestamp that is the minimum of getOutputTime applied to the timestamp of all of the non-late KV<K, V> that were used as input to the GroupByKey. The watermark is also prevented from advancing past this minimum timestamp until after the KV<K, Iterable<V>> has been output.

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

isNonMerging

public boolean isNonMerging()

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

assignsToSingleWindow

public boolean assignsToSingleWindow()

Returns true if this WindowFn assigns each element to a single window.