Package 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:
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:

  • Constructor Details

    • WindowFn

      public WindowFn()

  • Method Details

    • assignWindows

      public abstract Collection<W> assignWindows(WindowFn<T,W>.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<T,W>.MergeContext c) throws Exception
      Does whatever merging of windows is necessary.

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

      Throws:
      Exception

    • isCompatible

      @Deprecated public abstract boolean isCompatible(WindowFn<?,?> other)
      Deprecated.
      please override verifyCompatibility to throw a useful error message; we will remove isCompatible at version 3.0.0
      Returns whether this performs the same merging as the given WindowFn.

    • verifyCompatibility

      public void verifyCompatibility(WindowFn<?,?> other) throws IncompatibleWindowException
      Throw IncompatibleWindowException if this WindowFn does not perform the same merging as the given $WindowFn.
      Throws:
      IncompatibleWindowException - if compared WindowFns are not compatible.

    • windowCoder

      public abstract Coder<W> windowCoder()
      Returns the Coder used for serializing the windows used by this windowFn.

    • getDefaultWindowMappingFn

      public abstract WindowMappingFn<W> getDefaultWindowMappingFn()
      Returns the default WindowMappingFn to use to map main input windows to side input windows. This should accept arbitrary main input windows, and produce a BoundedWindow that can be produced by this WindowFn.

    • isNonMerging

      public boolean isNonMerging()
      Returns true if this WindowFn never needs to merge any windows.

    • assignsToOneWindow

      public boolean assignsToOneWindow()
      Returns true if this WindowFn always assigns an element to exactly one window.

      If this varies per-element, or cannot be determined, conservatively return false.

      By default, returns false.

    • getWindowTypeDescriptor

      public TypeDescriptor<W> getWindowTypeDescriptor()
      Returns a TypeDescriptor capturing what is known statically about the window type of this WindowFn instance's most-derived class.

      In the normal case of a concrete WindowFn subclass with no generic type parameters of its own (including anonymous inner classes), this will be a complete non-generic type.

    • 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: