com.google.cloud.dataflow.sdk.transforms.windowing.Sessions Maven / Gradle / Ivy

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/*
 * Copyright (C) 2015 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.cloud.dataflow.sdk.transforms.windowing;

import com.google.cloud.dataflow.sdk.coders.Coder;

import org.joda.time.Duration;
import org.joda.time.Instant;

import java.util.Arrays;
import java.util.Collection;

/**
 * A {@link WindowFn} windowing values into sessions separated by {@link #gapDuration}-long
 * periods with no elements.
 *
 *  For example, in order to window data into session with at least 10 minute
 * gaps in between them:
 * 
 {@code
 * PCollection pc = ...;
 * PCollection windowed_pc = pc.apply(
 *   Window.into(Sessions.withGapDuration(Duration.standardMinutes(10))));
 * } 
 */
public class Sessions extends WindowFn {
  private static final long serialVersionUID = 0;

  /**
   * Duration of the gaps between sessions.
   */
  private final Duration gapDuration;

  /**
   * Creates a {@code Sessions} {@link WindowFn} with the specified gap duration.
   */
  public static Sessions withGapDuration(Duration gapDuration) {
    return new Sessions(gapDuration);
  }

  /**
   * Creates a {@code Sessions} {@link WindowFn} with the specified gap duration.
   */
  private Sessions(Duration gapDuration) {
    this.gapDuration = gapDuration;
  }

  @Override
  public Collection assignWindows(AssignContext c) {
    // Assign each element into a window from its timestamp until gapDuration in the
    // future.  Overlapping windows (representing elements within gapDuration of
    // each other) will be merged.
    return Arrays.asList(new IntervalWindow(c.timestamp(), gapDuration));
  }

  @Override
  public void mergeWindows(MergeContext c) throws Exception {
    MergeOverlappingIntervalWindows.mergeWindows(c);
  }

  @Override
  public Coder windowCoder() {
    return IntervalWindow.getCoder();
  }

  @Override
  public boolean isCompatible(WindowFn other) {
    return other instanceof Sessions;
  }

  @Override
  public IntervalWindow getSideInputWindow(BoundedWindow window) {
    throw new UnsupportedOperationException("Sessions is not allowed in side inputs");
  }

  public Duration getGapDuration() {
    return gapDuration;
  }

  @Override
  public Instant getOutputTime(Instant inputTimestamp, IntervalWindow window) {
    return inputTimestamp;
  }
}