聊聊flink的Session Window

@PublicEvolving
public abstract class MergingWindowAssigner<T, W extends Window> extends WindowAssigner<T, W> {
    private static final long serialVersionUID = 1L;
​
    /**
     * Determines which windows (if any) should be merged.
     *
     * @param windows The window candidates.
     * @param callback A callback that can be invoked to signal which windows should be merged.
     */
    public abstract void mergeWindows(Collection<W> windows, MergeCallback<W> callback);
​
    /**
     * Callback to be used in {@link #mergeWindows(Collection, MergeCallback)} for specifying which
     * windows should be merged.
     */
    public interface MergeCallback<W> {
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        /**
         * Specifies that the given windows should be merged into the result window.
         *
         * @param toBeMerged The list of windows that should be merged into one window.
         * @param mergeResult The resulting merged window.
         */
        void merge(Collection<W> toBeMerged, W mergeResult);
    }
}

public class EventTimeSessionWindows extends MergingWindowAssigner<Object, TimeWindow> {
    private static final long serialVersionUID = 1L;
​
    protected long sessionTimeout;
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    protected EventTimeSessionWindows(long sessionTimeout) {
        if (sessionTimeout <= 0) {
            throw new IllegalArgumentException("EventTimeSessionWindows parameters must satisfy 0 < size");
        }
​
        this.sessionTimeout = sessionTimeout;
    }
​
    @Override
    public Collection<TimeWindow> assignWindows(Object element, long timestamp, WindowAssignerContext context) {
        return Collections.singletonList(new TimeWindow(timestamp, timestamp + sessionTimeout));
    }
​
    @Override
    public Trigger<Object, TimeWindow> getDefaultTrigger(StreamExecutionEnvironment env) {
        return EventTimeTrigger.create();
    }
​
    @Override
    public String toString() {
        return "EventTimeSessionWindows(" + sessionTimeout + ")";
    }
​
    /**
     * Creates a new {@code SessionWindows} {@link WindowAssigner} that assigns
     * elements to sessions based on the element timestamp.
     *
     * @param size The session timeout, i.e. the time gap between sessions
     * @return The policy.
     */
    public static EventTimeSessionWindows withGap(Time size) {
        return new EventTimeSessionWindows(size.toMilliseconds());
    }
​
    /**
     * Creates a new {@code SessionWindows} {@link WindowAssigner} that assigns
     * elements to sessions based on the element timestamp.
     *
     * @param sessionWindowTimeGapExtractor The extractor to use to extract the time gap from the input elements
     * @return The policy.
     */
    @PublicEvolving
    public static <T> DynamicEventTimeSessionWindows<T> withDynamicGap(SessionWindowTimeGapExtractor<T> sessionWindowTimeGapExtractor) {
        return new DynamicEventTimeSessionWindows<>(sessionWindowTimeGapExtractor);
    }
​
    @Override
    public TypeSerializer<TimeWindow> getWindowSerializer(ExecutionConfig executionConfig) {
        return new TimeWindow.Serializer();
    }
​
    @Override
    public boolean isEventTime() {
        return true;
    }
​
    /**
     * Merge overlapping {@link TimeWindow}s.
     */
    public void mergeWindows(Collection<TimeWindow> windows, MergingWindowAssigner.MergeCallback<TimeWindow> c) {
        TimeWindow.mergeWindows(windows, c);
    }
​
}

public class ProcessingTimeSessionWindows extends MergingWindowAssigner<Object, TimeWindow> {
    private static final long serialVersionUID = 1L;
​
    protected long sessionTimeout;
​
    protected ProcessingTimeSessionWindows(long sessionTimeout) {
        if (sessionTimeout <= 0) {
            throw new IllegalArgumentException("ProcessingTimeSessionWindows parameters must satisfy 0 < size");
        }
​
        this.sessionTimeout = sessionTimeout;
    }
​
    @Override
    public Collection<TimeWindow> assignWindows(Object element, long timestamp, WindowAssignerContext context) {
        long currentProcessingTime = context.getCurrentProcessingTime();
        return Collections.singletonList(new TimeWindow(currentProcessingTime, currentProcessingTime + sessionTimeout));
    }
​
    @Override
    public Trigger<Object, TimeWindow> getDefaultTrigger(StreamExecutionEnvironment env) {
        return ProcessingTimeTrigger.create();
    }
​
    @Override
    public String toString() {
        return "ProcessingTimeSessionWindows(" + sessionTimeout + ")";
    }
​
    /**
     * Creates a new {@code SessionWindows} {@link WindowAssigner} that assigns
     * elements to sessions based on the element timestamp.
     *
     * @param size The session timeout, i.e. the time gap between sessions
     * @return The policy.
     */
    public static ProcessingTimeSessionWindows withGap(Time size) {
        return new ProcessingTimeSessionWindows(size.toMilliseconds());
    }
​
    /**
     * Creates a new {@code SessionWindows} {@link WindowAssigner} that assigns
     * elements to sessions based on the element timestamp.
     *
     * @param sessionWindowTimeGapExtractor The extractor to use to extract the time gap from the input elements
     * @return The policy.
     */
    @PublicEvolving
    public static <T> DynamicProcessingTimeSessionWindows<T> withDynamicGap(SessionWindowTimeGapExtractor<T> sessionWindowTimeGapExtractor) {
        return new DynamicProcessingTimeSessionWindows<>(sessionWindowTimeGapExtractor);
    }
​
    @Override
    public TypeSerializer<TimeWindow> getWindowSerializer(ExecutionConfig executionConfig) {
        return new TimeWindow.Serializer();
    }
​
    @Override
    public boolean isEventTime() {
        return false;
    }
​
    /**
     * Merge overlapping {@link TimeWindow}s.
     */
    public void mergeWindows(Collection<TimeWindow> windows, MergeCallback<TimeWindow> c) {
        TimeWindow.mergeWindows(windows, c);
    }
​
}

@PublicEvolving
public interface SessionWindowTimeGapExtractor<T> extends Serializable {
    /**
     * Extracts the session time gap.
     * @param element The input element.
     * @return The session time gap in milliseconds.
     */
    long extract(T element);
}

@PublicEvolving
public class DynamicEventTimeSessionWindows<T> extends MergingWindowAssigner<T, TimeWindow> {
    private static final long serialVersionUID = 1L;
​
    protected SessionWindowTimeGapExtractor<T> sessionWindowTimeGapExtractor;
​
    protected DynamicEventTimeSessionWindows(SessionWindowTimeGapExtractor<T> sessionWindowTimeGapExtractor) {
        this.sessionWindowTimeGapExtractor = sessionWindowTimeGapExtractor;
    }
​
    @Override
    public Collection<TimeWindow> assignWindows(T element, long timestamp, WindowAssignerContext context) {
        long sessionTimeout = sessionWindowTimeGapExtractor.extract(element);
        if (sessionTimeout <= 0) {
            throw new IllegalArgumentException("Dynamic session time gap must satisfy 0 < gap");
        }
        return Collections.singletonList(new TimeWindow(timestamp, timestamp + sessionTimeout));
    }
​
    @SuppressWarnings("unchecked")
    @Override
    public Trigger<T, TimeWindow> getDefaultTrigger(StreamExecutionEnvironment env) {
        return (Trigger<T, TimeWindow>) EventTimeTrigger.create();
    }
​
    @Override
    public String toString() {
        return "DynamicEventTimeSessionWindows()";
    }
​
    /**
     * Creates a new {@code SessionWindows} {@link WindowAssigner} that assigns
     * elements to sessions based on the element timestamp.
     *
     * @param sessionWindowTimeGapExtractor The extractor to use to extract the time gap from the input elements
     * @return The policy.
     */
    public static <T> DynamicEventTimeSessionWindows<T> withDynamicGap(SessionWindowTimeGapExtractor<T> sessionWindowTimeGapExtractor) {
        return new DynamicEventTimeSessionWindows<>(sessionWindowTimeGapExtractor);
    }
​
    @Override
    public TypeSerializer<TimeWindow> getWindowSerializer(ExecutionConfig executionConfig) {
        return new TimeWindow.Serializer();
    }
​
    @Override
    public boolean isEventTime() {
        return true;
    }
​
    /**
     * Merge overlapping {@link TimeWindow}s.
     */
    public void mergeWindows(Collection<TimeWindow> windows, MergeCallback<TimeWindow> c) {
        TimeWindow.mergeWindows(windows, c);
    }
​
}

@PublicEvolving
public class DynamicProcessingTimeSessionWindows<T> extends MergingWindowAssigner<T, TimeWindow> {
    private static final long serialVersionUID = 1L;
​
    protected SessionWindowTimeGapExtractor<T> sessionWindowTimeGapExtractor;
​
    protected DynamicProcessingTimeSessionWindows(SessionWindowTimeGapExtractor<T> sessionWindowTimeGapExtractor) {
        this.sessionWindowTimeGapExtractor = sessionWindowTimeGapExtractor;
    }
​
    @Override
    public Collection<TimeWindow> assignWindows(T element, long timestamp, WindowAssignerContext context) {
        long currentProcessingTime = context.getCurrentProcessingTime();
        long sessionTimeout = sessionWindowTimeGapExtractor.extract(element);
        if (sessionTimeout <= 0) {
            throw new IllegalArgumentException("Dynamic session time gap must satisfy 0 < gap");
        }
        return Collections.singletonList(new TimeWindow(currentProcessingTime, currentProcessingTime + sessionTimeout));
    }
​
    @SuppressWarnings("unchecked")
    @Override
    public Trigger<T, TimeWindow> getDefaultTrigger(StreamExecutionEnvironment env) {
        return (Trigger<T, TimeWindow>) ProcessingTimeTrigger.create();
    }
​
    @Override
    public String toString() {
        return "DynamicProcessingTimeSessionWindows()";
    }
​
    /**
     * Creates a new {@code SessionWindows} {@link WindowAssigner} that assigns
     * elements to sessions based on the element timestamp.
     *
     * @param sessionWindowTimeGapExtractor The extractor to use to extract the time gap from the input elements
     * @return The policy.
     */
    public static <T> DynamicProcessingTimeSessionWindows<T> withDynamicGap(SessionWindowTimeGapExtractor<T> sessionWindowTimeGapExtractor) {
        return new DynamicProcessingTimeSessionWindows<>(sessionWindowTimeGapExtractor);
    }
​
    @Override
    public TypeSerializer<TimeWindow> getWindowSerializer(ExecutionConfig executionConfig) {
        return new TimeWindow.Serializer();
    }
​
    @Override
    public boolean isEventTime() {
        return false;
    }
​
    /**
     * Merge overlapping {@link TimeWindow}s.
     */
    public void mergeWindows(Collection<TimeWindow> windows, MergeCallback<TimeWindow> c) {
        TimeWindow.mergeWindows(windows, c);
    }
​
}