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:

java.io.Serializable

Direct Known Subclasses:

InvalidWindows, NonMergingWindowFn, Sessions

public abstract class WindowFn<T,W extends BoundedWindow>
extends java.lang.Object
implements java.io.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

Methods

Modifier and Type	Method and Description
abstract java.util.Collection<W>	assignWindows(WindowFn.AssignContext c) Given a timestamp and element, returns the set of windows into which it should be placed.
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.
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 java.util.Collection<W> assignWindows(WindowFn.AssignContext c)
                                                                     throws java.lang.Exception

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

Throws:

java.lang.Exception

mergeWindows

public abstract void mergeWindows(WindowFn.MergeContext c)
                           throws java.lang.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:

java.lang.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 W getSideInputWindow(BoundedWindow window)

Returns the window of the side input corresponding to the given window of the main input. By default, this runs assignWindows over a non-existent element whose timestamp is the maxTimestamp() of the input window.

For example, if both the main and side inputs are windowed by FixedWindows, the side input corresponding to a particular main input element will be the one in the same window as that element.

Authors of custom WindowFns should override this if that is not the desired behavior for side inputs with their WindowFn.