聊聊flink DataStream的join操作

stream.join(otherStream)
    .where(<KeySelector>)
    .equalTo(<KeySelector>)
    .window(<WindowAssigner>)
    .apply(<JoinFunction>)
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• 这里首先调用join，与另外一个stream合并，返回的是JoinedStreams，之后就可以调用JoinedStreams的where操作来构建Where对象构造条件；Where有equalTo操作可以构造EqualTo，而EqualTo有window操作可以构造WithWindow，而WithWindow可以设置windowAssigner、trigger、evictor、allowedLateness，它提供apply操作

DataStream.join

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/DataStream.java

@Public
public class DataStream<T> {
	//......

	/**
	 * Creates a join operation. See {@link JoinedStreams} for an example of how the keys
	 * and window can be specified.
	 */
	public <T2> JoinedStreams<T, T2> join(DataStream<T2> otherStream) {
		return new JoinedStreams<>(this, otherStream);
	}

	//......
}
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• DataStream提供了join方法，用于执行join操作，它返回的是JoinedStreams

JoinedStreams

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/JoinedStreams.java

@Public
public class JoinedStreams<T1, T2> {

	/** The first input stream. */
	private final DataStream<T1> input1;

	/** The second input stream. */
	private final DataStream<T2> input2;

	public JoinedStreams(DataStream<T1> input1, DataStream<T2> input2) {
		this.input1 = requireNonNull(input1);
		this.input2 = requireNonNull(input2);
	}

	public <KEY> Where<KEY> where(KeySelector<T1, KEY> keySelector)  {
		requireNonNull(keySelector);
		final TypeInformation<KEY> keyType = TypeExtractor.getKeySelectorTypes(keySelector, input1.getType());
		return where(keySelector, keyType);
	}

	public <KEY> Where<KEY> where(KeySelector<T1, KEY> keySelector, TypeInformation<KEY> keyType)  {
		requireNonNull(keySelector);
		requireNonNull(keyType);
		return new Where<>(input1.clean(keySelector), keyType);
	}

	//......
}
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• JoinedStreams主要是提供where操作来构建Where对象

Where

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/JoinedStreams.java

@Public
	public class Where<KEY> {

		private final KeySelector<T1, KEY> keySelector1;
		private final TypeInformation<KEY> keyType;

		Where(KeySelector<T1, KEY> keySelector1, TypeInformation<KEY> keyType) {
			this.keySelector1 = keySelector1;
			this.keyType = keyType;
		}

		public EqualTo equalTo(KeySelector<T2, KEY> keySelector)  {
			requireNonNull(keySelector);
			final TypeInformation<KEY> otherKey = TypeExtractor.getKeySelectorTypes(keySelector, input2.getType());
			return equalTo(keySelector, otherKey);
		}

		public EqualTo equalTo(KeySelector<T2, KEY> keySelector, TypeInformation<KEY> keyType)  {
			requireNonNull(keySelector);
			requireNonNull(keyType);

			if (!keyType.equals(this.keyType)) {
				throw new IllegalArgumentException("The keys for the two inputs are not equal: " +
						"first key = " + this.keyType + " , second key = " + keyType);
			}

			return new EqualTo(input2.clean(keySelector));
		}

		//......

	}
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• Where对象主要提供equalTo操作用于构建EqualTo对象

EqualTo

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/JoinedStreams.java

@Public
		public class EqualTo {

			private final KeySelector<T2, KEY> keySelector2;

			EqualTo(KeySelector<T2, KEY> keySelector2) {
				this.keySelector2 = requireNonNull(keySelector2);
			}

			/**
			 * Specifies the window on which the join operation works.
			 */
			@PublicEvolving
			public <W extends Window> WithWindow<T1, T2, KEY, W> window(WindowAssigner<? super TaggedUnion<T1, T2>, W> assigner) {
				return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType, assigner, null, null, null);
			}
		}
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• EqualTo对象提供window操作用于构建WithWindow对象

WithWindow

/flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/JoinedStreams.java

@Public
	public static class WithWindow<T1, T2, KEY, W extends Window> {

		private final DataStream<T1> input1;
		private final DataStream<T2> input2;

		private final KeySelector<T1, KEY> keySelector1;
		private final KeySelector<T2, KEY> keySelector2;
		private final TypeInformation<KEY> keyType;

		private final WindowAssigner<? super TaggedUnion<T1, T2>, W> windowAssigner;

		private final Trigger<? super TaggedUnion<T1, T2>, ? super W> trigger;

		private final Evictor<? super TaggedUnion<T1, T2>, ? super W> evictor;

		private final Time allowedLateness;

		private CoGroupedStreams.WithWindow<T1, T2, KEY, W> coGroupedWindowedStream;

		@PublicEvolving
		protected WithWindow(DataStream<T1> input1,
				DataStream<T2> input2,
				KeySelector<T1, KEY> keySelector1,
				KeySelector<T2, KEY> keySelector2,
				TypeInformation<KEY> keyType,
				WindowAssigner<? super TaggedUnion<T1, T2>, W> windowAssigner,
				Trigger<? super TaggedUnion<T1, T2>, ? super W> trigger,
				Evictor<? super TaggedUnion<T1, T2>, ? super W> evictor,
				Time allowedLateness) {

			this.input1 = requireNonNull(input1);
			this.input2 = requireNonNull(input2);

			this.keySelector1 = requireNonNull(keySelector1);
			this.keySelector2 = requireNonNull(keySelector2);
			this.keyType = requireNonNull(keyType);

			this.windowAssigner = requireNonNull(windowAssigner);

			this.trigger = trigger;
			this.evictor = evictor;

			this.allowedLateness = allowedLateness;
		}

		@PublicEvolving
		public WithWindow<T1, T2, KEY, W> trigger(Trigger<? super TaggedUnion<T1, T2>, ? super W> newTrigger) {
			return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
					windowAssigner, newTrigger, evictor, allowedLateness);
		}

		@PublicEvolving
		public WithWindow<T1, T2, KEY, W> evictor(Evictor<? super TaggedUnion<T1, T2>, ? super W> newEvictor) {
			return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
					windowAssigner, trigger, newEvictor, allowedLateness);
		}

		@PublicEvolving
		public WithWindow<T1, T2, KEY, W> allowedLateness(Time newLateness) {
			return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
				windowAssigner, trigger, evictor, newLateness);
		}

		public <T> DataStream<T> apply(JoinFunction<T1, T2, T> function) {
			TypeInformation<T> resultType = TypeExtractor.getBinaryOperatorReturnType(
				function,
				JoinFunction.class,
				0,
				1,
				2,
				TypeExtractor.NO_INDEX,
				input1.getType(),
				input2.getType(),
				"Join",
				false);

			return apply(function, resultType);
		}

		@PublicEvolving
		@Deprecated
		public <T> SingleOutputStreamOperator<T> with(JoinFunction<T1, T2, T> function) {
			return (SingleOutputStreamOperator<T>) apply(function);
		}

		public <T> DataStream<T> apply(FlatJoinFunction<T1, T2, T> function, TypeInformation<T> resultType) {
			//clean the closure
			function = input1.getExecutionEnvironment().clean(function);

			coGroupedWindowedStream = input1.coGroup(input2)
				.where(keySelector1)
				.equalTo(keySelector2)
				.window(windowAssigner)
				.trigger(trigger)
				.evictor(evictor)
				.allowedLateness(allowedLateness);

			return coGroupedWindowedStream
					.apply(new FlatJoinCoGroupFunction<>(function), resultType);
		}

		@PublicEvolving
		@Deprecated
		public <T> SingleOutputStreamOperator<T> with(FlatJoinFunction<T1, T2, T> function, TypeInformation<T> resultType) {
			return (SingleOutputStreamOperator<T>) apply(function, resultType);
		}

		public <T> DataStream<T> apply(FlatJoinFunction<T1, T2, T> function) {
			TypeInformation<T> resultType = TypeExtractor.getBinaryOperatorReturnType(
				function,
				FlatJoinFunction.class,
				0,
				1,
				2,
				new int[]{2, 0},
				input1.getType(),
				input2.getType(),
				"Join",
				false);

			return apply(function, resultType);
		}

		@PublicEvolving
		@Deprecated
		public <T> SingleOutputStreamOperator<T> with(FlatJoinFunction<T1, T2, T> function) {
			return (SingleOutputStreamOperator<T>) apply(function);
		}

		public <T> DataStream<T> apply(JoinFunction<T1, T2, T> function, TypeInformation<T> resultType) {
			//clean the closure
			function = input1.getExecutionEnvironment().clean(function);

			coGroupedWindowedStream = input1.coGroup(input2)
				.where(keySelector1)
				.equalTo(keySelector2)
				.window(windowAssigner)
				.trigger(trigger)
				.evictor(evictor)
				.allowedLateness(allowedLateness);

			return coGroupedWindowedStream
					.apply(new JoinCoGroupFunction<>(function), resultType);
		}

		@PublicEvolving
		@Deprecated
		public <T> SingleOutputStreamOperator<T> with(JoinFunction<T1, T2, T> function, TypeInformation<T> resultType) {
			return (SingleOutputStreamOperator<T>) apply(function, resultType);
		}

		@VisibleForTesting
		Time getAllowedLateness() {
			return allowedLateness;
		}

		@VisibleForTesting
		CoGroupedStreams.WithWindow<T1, T2, KEY, W> getCoGroupedWindowedStream() {
			return coGroupedWindowedStream;
		}
	}
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with操作被标记为废弃
JoinFunction使用JoinCoGroupFunction包装，FlatJoinFunction使用FlatJoinCoGroupFunction包装

JoinFunction

flink-core-1.7.0-sources.jar!/org/apache/flink/api/common/functions/JoinFunction.java

@Public
@FunctionalInterface
public interface JoinFunction<IN1, IN2, OUT> extends Function, Serializable {

	/**
	 * The join method, called once per joined pair of elements.
	 *
	 * @param first The element from first input.
	 * @param second The element from second input.
	 * @return The resulting element.
	 *
	 * @throws Exception This method may throw exceptions. Throwing an exception will cause the operation
	 *                   to fail and may trigger recovery.
	 */
	OUT join(IN1 first, IN2 second) throws Exception;
}
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• JoinFunction继承了Function、Serializable，它定义了join操作，默认是inner join的语义，如果需要outer join，可以使用CoGroupFunction

FlatJoinFunction

flink-core-1.7.0-sources.jar!/org/apache/flink/api/common/functions/FlatJoinFunction.java

@Public
@FunctionalInterface
public interface FlatJoinFunction<IN1, IN2, OUT> extends Function, Serializable {

	/**
	 * The join method, called once per joined pair of elements.
	 *
	 * @param first The element from first input.
	 * @param second The element from second input.
	 * @param out The collector used to return zero, one, or more elements.
	 *
	 * @throws Exception This method may throw exceptions. Throwing an exception will cause the operation
	 *                   to fail and may trigger recovery.
	 */
	void join (IN1 first, IN2 second, Collector<OUT> out) throws Exception;
}
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• FlatJoinFunction继承了Function、Serializable，它定义了join操作，默认是inner join的语义，如果需要outer join，可以使用CoGroupFunction；与JoinFunction的join方法不同，FlatJoinFunction的join方法多了Collector参数，可以用来发射0条、1条或者多条数据，所以是Flat命名

CoGroupedStreams

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java

@Public
public class CoGroupedStreams<T1, T2> {
	//......

@Public
	public static class WithWindow<T1, T2, KEY, W extends Window> {
		private final DataStream<T1> input1;
		private final DataStream<T2> input2;

		private final KeySelector<T1, KEY> keySelector1;
		private final KeySelector<T2, KEY> keySelector2;

		private final TypeInformation<KEY> keyType;

		private final WindowAssigner<? super TaggedUnion<T1, T2>, W> windowAssigner;

		private final Trigger<? super TaggedUnion<T1, T2>, ? super W> trigger;

		private final Evictor<? super TaggedUnion<T1, T2>, ? super W> evictor;

		private final Time allowedLateness;

		private WindowedStream<TaggedUnion<T1, T2>, KEY, W> windowedStream;

		protected WithWindow(DataStream<T1> input1,
				DataStream<T2> input2,
				KeySelector<T1, KEY> keySelector1,
				KeySelector<T2, KEY> keySelector2,
				TypeInformation<KEY> keyType,
				WindowAssigner<? super TaggedUnion<T1, T2>, W> windowAssigner,
				Trigger<? super TaggedUnion<T1, T2>, ? super W> trigger,
				Evictor<? super TaggedUnion<T1, T2>, ? super W> evictor,
				Time allowedLateness) {
			this.input1 = input1;
			this.input2 = input2;

			this.keySelector1 = keySelector1;
			this.keySelector2 = keySelector2;
			this.keyType = keyType;

			this.windowAssigner = windowAssigner;
			this.trigger = trigger;
			this.evictor = evictor;

			this.allowedLateness = allowedLateness;
		}

		@PublicEvolving
		public WithWindow<T1, T2, KEY, W> trigger(Trigger<? super TaggedUnion<T1, T2>, ? super W> newTrigger) {
			return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
					windowAssigner, newTrigger, evictor, allowedLateness);
		}

		@PublicEvolving
		public WithWindow<T1, T2, KEY, W> evictor(Evictor<? super TaggedUnion<T1, T2>, ? super W> newEvictor) {
			return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
					windowAssigner, trigger, newEvictor, allowedLateness);
		}

		@PublicEvolving
		public WithWindow<T1, T2, KEY, W> allowedLateness(Time newLateness) {
			return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
					windowAssigner, trigger, evictor, newLateness);
		}

		public <T> DataStream<T> apply(CoGroupFunction<T1, T2, T> function) {

			TypeInformation<T> resultType = TypeExtractor.getCoGroupReturnTypes(
				function,
				input1.getType(),
				input2.getType(),
				"CoGroup",
				false);

			return apply(function, resultType);
		}

		public <T> DataStream<T> apply(CoGroupFunction<T1, T2, T> function, TypeInformation<T> resultType) {
			//clean the closure
			function = input1.getExecutionEnvironment().clean(function);

			UnionTypeInfo<T1, T2> unionType = new UnionTypeInfo<>(input1.getType(), input2.getType());
			UnionKeySelector<T1, T2, KEY> unionKeySelector = new UnionKeySelector<>(keySelector1, keySelector2);

			DataStream<TaggedUnion<T1, T2>> taggedInput1 = input1
					.map(new Input1Tagger<T1, T2>())
					.setParallelism(input1.getParallelism())
					.returns(unionType);
			DataStream<TaggedUnion<T1, T2>> taggedInput2 = input2
					.map(new Input2Tagger<T1, T2>())
					.setParallelism(input2.getParallelism())
					.returns(unionType);

			DataStream<TaggedUnion<T1, T2>> unionStream = taggedInput1.union(taggedInput2);

			// we explicitly create the keyed stream to manually pass the key type information in
			windowedStream =
					new KeyedStream<TaggedUnion<T1, T2>, KEY>(unionStream, unionKeySelector, keyType)
					.window(windowAssigner);

			if (trigger != null) {
				windowedStream.trigger(trigger);
			}
			if (evictor != null) {
				windowedStream.evictor(evictor);
			}
			if (allowedLateness != null) {
				windowedStream.allowedLateness(allowedLateness);
			}

			return windowedStream.apply(new CoGroupWindowFunction<T1, T2, T, KEY, W>(function), resultType);
		}

		//......

	}

	//......
}
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• CoGroupedStreams的整体类结构跟JoinedStreams很像，CoGroupedStreams提供where操作来构建Where对象；Where对象主要提供equalTo操作用于构建EqualTo对象；EqualTo对象提供window操作用于构建WithWindow对象；WithWindow可以设置windowAssigner、trigger、evictor、allowedLateness，它提供apply操作；其中一个不同的地方是CoGroupedStreams定义的WithWindow对象的apply操作接收的Function是CoGroupFunction类型，而JoinedStreams定义的WithWindow对象的apply操作接收的Function类型是JoinFunction或FlatJoinFunction

CoGroupFunction

flink-core-1.7.0-sources.jar!/org/apache/flink/api/common/functions/CoGroupFunction.java

@Public
@FunctionalInterface
public interface CoGroupFunction<IN1, IN2, O> extends Function, Serializable {

	/**
	 * This method must be implemented to provide a user implementation of a
	 * coGroup. It is called for each pair of element groups where the elements share the
	 * same key.
	 *
	 * @param first The records from the first input.
	 * @param second The records from the second.
	 * @param out A collector to return elements.
	 *
	 * @throws Exception The function may throw Exceptions, which will cause the program to cancel,
	 *                   and may trigger the recovery logic.
	 */
	void coGroup(Iterable<IN1> first, Iterable<IN2> second, Collector<O> out) throws Exception;
}
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• CoGroupFunction继承了Function、Serializable，它定义了coGroup操作，可以用来实现outer join，其参数使用的是Iterable，而JoinFunction与FlatJoinFunction的join参数使用的是单个对象类型

WrappingFunction

flink-java-1.7.0-sources.jar!/org/apache/flink/api/java/operators/translation/WrappingFunction.java

@Internal
public abstract class WrappingFunction<T extends Function> extends AbstractRichFunction {

	private static final long serialVersionUID = 1L;

	protected T wrappedFunction;

	protected WrappingFunction(T wrappedFunction) {
		this.wrappedFunction = wrappedFunction;
	}

	@Override
	public void open(Configuration parameters) throws Exception {
		FunctionUtils.openFunction(this.wrappedFunction, parameters);
	}

	@Override
	public void close() throws Exception {
		FunctionUtils.closeFunction(this.wrappedFunction);
	}

	@Override
	public void setRuntimeContext(RuntimeContext t) {
		super.setRuntimeContext(t);

		FunctionUtils.setFunctionRuntimeContext(this.wrappedFunction, t);
	}

	public T getWrappedFunction () {
		return this.wrappedFunction;
	}
}
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• WrappingFunction继承了AbstractRichFunction，这里它覆盖了父类的open、close、setRuntimeContext方法，用于管理wrappedFunction

JoinCoGroupFunction

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/JoinedStreams.java

/**
	 * CoGroup function that does a nested-loop join to get the join result.
	 */
	private static class JoinCoGroupFunction<T1, T2, T>
			extends WrappingFunction<JoinFunction<T1, T2, T>>
			implements CoGroupFunction<T1, T2, T> {
		private static final long serialVersionUID = 1L;

		public JoinCoGroupFunction(JoinFunction<T1, T2, T> wrappedFunction) {
			super(wrappedFunction);
		}

		@Override
		public void coGroup(Iterable<T1> first, Iterable<T2> second, Collector<T> out) throws Exception {
			for (T1 val1: first) {
				for (T2 val2: second) {
					out.collect(wrappedFunction.join(val1, val2));
				}
			}
		}
	}
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• JoinCoGroupFunction继承了WrappingFunction，同时实现CoGroupFunction接口定义的coGroup方法，默认是遍历第一个集合，对其每个元素遍历第二个集合，挨个执行wrappedFunction.join，然后发射join数据
• JoinedStreams定义了私有静态类JoinCoGroupFunction，JoinedStreams的WithWindow对象的apply方法内部使用它将JoinFunction进行包装，然后去调用CoGroupedStreams的WithWindow的apply方法
• JoinFunction定义的join方法，接收的是两个对象类型参数，而JoinCoGroupFunction定义的coGroup方法，接收的两个Iterable类型参数

FlatJoinCoGroupFunction

flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/JoinedStreams.java

/**
	 * CoGroup function that does a nested-loop join to get the join result. (FlatJoin version)
	 */
	private static class FlatJoinCoGroupFunction<T1, T2, T>
			extends WrappingFunction<FlatJoinFunction<T1, T2, T>>
			implements CoGroupFunction<T1, T2, T> {
		private static final long serialVersionUID = 1L;

		public FlatJoinCoGroupFunction(FlatJoinFunction<T1, T2, T> wrappedFunction) {
			super(wrappedFunction);
		}

		@Override
		public void coGroup(Iterable<T1> first, Iterable<T2> second, Collector<T> out) throws Exception {
			for (T1 val1: first) {
				for (T2 val2: second) {
					wrappedFunction.join(val1, val2, out);
				}
			}
		}
	}
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• FlatJoinCoGroupFunction继承了WrappingFunction，同时实现CoGroupFunction接口定义的coGroup方法，默认是遍历第一个集合，对其每个元素遍历第二个集合，挨个执行wrappedFunction.join，然后发射join数据
• JoinedStreams定义了私有静态类FlatJoinCoGroupFunction，JoinedStreams的WithWindow对象的apply方法内部使用它将FlatJoinFunction进行包装，然后去调用CoGroupedStreams的WithWindow的apply方法
• FlatJoinFunction定义的join方法，接收的是两个对象类型参数，而FlatJoinCoGroupFunction定义的coGroup方法，接收的两个Iterable类型参数