WindowFn (Google Cloud Dataflow SDK 1.9.1 API)

Google Cloud Dataflow SDK for Java, version 1.9.1

Warning: Dataflow SDK 1.x for Java is unsupported as of October 16, 2018. After August 12, 2020, you can use unsupported SDKs temporarily while you upgrade your pipelines. For more information, see Using an unsupported SDK.

For information on migrating from the 1.x SDK, see Migrating from Dataflow SDK 1.x for Java.

Note: If you are using Cloud Dataflow SDK version 2.x, see the Apache Beam API reference documentation.

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:

  HasDisplayData, Serializable

  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(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

    All Methods Instance Methods Abstract Methods Concrete Methods Deprecated Methods 

    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 one of the appropriate OutputTimeFns, 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.
    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(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 one of the appropriate OutputTimeFns, 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.

    • 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