聊聊flink的Global Window

序

本文主要研究一下flink的Global Window

GlobalWindow

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/windowing/windows/GlobalWindow.java

@PublicEvolving
public class GlobalWindow extends Window {

	private static final GlobalWindow INSTANCE = new GlobalWindow();

	private GlobalWindow() { }

	public static GlobalWindow get() {
		return INSTANCE;
	}

	@Override
	public long maxTimestamp() {
		return Long.MAX_VALUE;
	}

	@Override
	public boolean equals(Object o) {
		return this == o || !(o == null || getClass() != o.getClass());
	}

	@Override
	public int hashCode() {
		return 0;
	}

	@Override
	public String toString() {
		return "GlobalWindow";
	}

	/**
	 * A {@link TypeSerializer} for {@link GlobalWindow}.
	 */
	public static class Serializer extends TypeSerializerSingleton<GlobalWindow> {
		private static final long serialVersionUID = 1L;

		@Override
		public boolean isImmutableType() {
			return true;
		}

		@Override
		public GlobalWindow createInstance() {
			return GlobalWindow.INSTANCE;
		}

		@Override
		public GlobalWindow copy(GlobalWindow from) {
			return from;
		}

		@Override
		public GlobalWindow copy(GlobalWindow from, GlobalWindow reuse) {
			return from;
		}

		@Override
		public int getLength() {
			return 0;
		}

		@Override
		public void serialize(GlobalWindow record, DataOutputView target) throws IOException {
			target.writeByte(0);
		}

		@Override
		public GlobalWindow deserialize(DataInputView source) throws IOException {
			source.readByte();
			return GlobalWindow.INSTANCE;
		}

		@Override
		public GlobalWindow deserialize(GlobalWindow reuse,
				DataInputView source) throws IOException {
			source.readByte();
			return GlobalWindow.INSTANCE;
		}

		@Override
		public void copy(DataInputView source, DataOutputView target) throws IOException {
			source.readByte();
			target.writeByte(0);
		}

		@Override
		public boolean canEqual(Object obj) {
			return obj instanceof Serializer;
		}
	}
}
复制代码

• GlobalWindow继承了Window，它的maxTimestamp方法与TimeWindow不同，TimeWindow有start和end属性，其maxTimestamp方法返回的是end-1；而GlobalWindow的maxTimestamp方法返回的是Long.MAX_VALUE；GlobalWindow定义了自己的Serializer

GlobalWindows

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/windowing/assigners/GlobalWindows.java

@PublicEvolving
public class GlobalWindows extends WindowAssigner<Object, GlobalWindow> {
	private static final long serialVersionUID = 1L;

	private GlobalWindows() {}

	@Override
	public Collection<GlobalWindow> assignWindows(Object element, long timestamp, WindowAssignerContext context) {
		return Collections.singletonList(GlobalWindow.get());
	}

	@Override
	public Trigger<Object, GlobalWindow> getDefaultTrigger(StreamExecutionEnvironment env) {
		return new NeverTrigger();
	}

	@Override
	public String toString() {
		return "GlobalWindows()";
	}

	/**
	 * Creates a new {@code GlobalWindows} {@link WindowAssigner} that assigns
	 * all elements to the same {@link GlobalWindow}.
	 *
	 * @return The global window policy.
	 */
	public static GlobalWindows create() {
		return new GlobalWindows();
	}

	/**
	 * A trigger that never fires, as default Trigger for GlobalWindows.
	 */
	@Internal
	public static class NeverTrigger extends Trigger<Object, GlobalWindow> {
		private static final long serialVersionUID = 1L;

		@Override
		public TriggerResult onElement(Object element, long timestamp, GlobalWindow window, TriggerContext ctx) {
			return TriggerResult.CONTINUE;
		}

		@Override
		public TriggerResult onEventTime(long time, GlobalWindow window, TriggerContext ctx) {
			return TriggerResult.CONTINUE;
		}

		@Override
		public TriggerResult onProcessingTime(long time, GlobalWindow window, TriggerContext ctx) {
			return TriggerResult.CONTINUE;
		}

		@Override
		public void clear(GlobalWindow window, TriggerContext ctx) throws Exception {}

		@Override
		public void onMerge(GlobalWindow window, OnMergeContext ctx) {
		}
	}

	@Override
	public TypeSerializer<GlobalWindow> getWindowSerializer(ExecutionConfig executionConfig) {
		return new GlobalWindow.Serializer();
	}

	@Override
	public boolean isEventTime() {
		return false;
	}
}
复制代码

• GlobalWindows继承了WindowAssigner，key类型为Object，窗口类型为GlobalWindow
• assignWindows方法返回的是GlobalWindow；getDefaultTrigger方法返回的是NeverTrigger；getWindowSerializer返回的是GlobalWindow.Serializer()；isEventTime返回的为false
• NeverTrigger继承了Trigger，其onElement、onProcessingTime、onProcessingTime返回的TriggerResult均为TriggerResult.CONTINUE

小结

• GlobalWindows继承了WindowAssigner，key类型为Object，窗口类型为GlobalWindow；GlobalWindow继承了Window，它的maxTimestamp方法与TimeWindow不同，TimeWindow有start和end属性，其maxTimestamp方法返回的是end-1；而GlobalWindow的maxTimestamp方法返回的是Long.MAX_VALUE；GlobalWindow定义了自己的Serializer
• GlobalWindows的assignWindows方法返回的是GlobalWindow；getDefaultTrigger方法返回的是NeverTrigger；getWindowSerializer返回的是GlobalWindow.Serializer()；isEventTime返回的为false
• NeverTrigger继承了Trigger，其onElement、onProcessingTime、onProcessingTime返回的TriggerResult均为TriggerResult.CONTINUE；该行为就是不做任何触发操作；如果需要触发操作，则需要在定义window操作时设置自定义的trigger，覆盖GlobalWindows默认的NeverTrigger

doc

• Global Windows