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.

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(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.
Instant	getOutputTime(Instant inputTimestamp, W window) Deprecated. Implement getOutputTimeFn() to return either the appropriate ElementaryOutputTimeFn or a custom OutputTimeFn extending OutputTimeFn.Defaults.
OutputTimeFn<? super W>	getOutputTimeFn() Provides a default implementation for WindowingStrategy.getOutputTimeFn().
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

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

Deprecated. Implement getOutputTimeFn() to return either the appropriate ElementaryOutputTimeFn or a custom OutputTimeFn extending OutputTimeFn.Defaults.

getOutputTimeFn

@Experimental(value=OUTPUT_TIME)
public OutputTimeFn<? super W> getOutputTimeFn()

Provides a default implementation for WindowingStrategy.getOutputTimeFn(). See the full specification there.

If this WindowFn doesn't produce overlapping windows, this need not (and probably should not) override any of the default implementations in OutputTimeFn.Defaults.

If this WindowFn does produce overlapping windows that can be predicted here, 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.

For example, a timestamp in a sliding window should be moved past the beginning of the next sliding window. See SlidingWindows.getOutputTimeFn().

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.