Windows — Window Specification For Time-Windowed Streaming Aggregations

Windows is the abstraction of window specifications that describe windows of fixed size and grace period.

Windows are used in KGroupedStream.windowedBy streaming operator (for time-windowed streaming aggregations).

Table 1. Windows API / Operators
Method Description


long gracePeriodMs()

Grace period (in milliseconds)

New events are added to windows until their grace period ends


long size()

Window size (in milliseconds)


Map<Long, W> windowsFor(final long timestamp)

Returns all the windows that contain the given timestamp, indexed by non-negative window start timestamps.

Used when KStreamWindowAggregateProcessor is requested to process a record

Table 2. Windows
Windows Description



Time-bound window specification for tumbling or hopping windows


Windows takes no arguments when created and simply initializes the internal registries and counters.

Windows is a Java abstract class and cannot be created directly. It is created indirectly when the concrete Windows are.

Windows defines a window maintain duration (aka retention time). The default window maintain duration is 1 day.

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