序
本文主要研究一下flink DataStream的window coGroup操作
实例
dataStream.coGroup(otherStream)
.where(0).equalTo(1)
.window(TumblingEventTimeWindows.of(Time.seconds(3)))
.apply (new CoGroupFunction () {...});- 这里展示了DataStream的window coGroup操作的基本用法
DataStream.coGroup
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/DataStream.java
@Public
public class DataStream {
//......
public CoGroupedStreams coGroup(DataStream otherStream) {
return new CoGroupedStreams<>(this, otherStream);
}
//......
} - DataStream的coGroup操作创建的是CoGroupedStreams
CoGroupedStreams
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java
@Public
public class CoGroupedStreams {
private final DataStream input1;
private final DataStream input2;
public CoGroupedStreams(DataStream input1, DataStream input2) {
this.input1 = requireNonNull(input1);
this.input2 = requireNonNull(input2);
}
public Where where(KeySelector keySelector) {
Preconditions.checkNotNull(keySelector);
final TypeInformation keyType = TypeExtractor.getKeySelectorTypes(keySelector, input1.getType());
return where(keySelector, keyType);
}
public Where where(KeySelector keySelector, TypeInformation keyType) {
Preconditions.checkNotNull(keySelector);
Preconditions.checkNotNull(keyType);
return new Where<>(input1.clean(keySelector), keyType);
}
//.......
} - CoGroupedStreams提供了where操作，用于指定input1的keySelector，它创建并返回Where对象
Where
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java
@Public
public class Where {
private final KeySelector keySelector1;
private final TypeInformation keyType;
Where(KeySelector keySelector1, TypeInformation keyType) {
this.keySelector1 = keySelector1;
this.keyType = keyType;
}
public EqualTo equalTo(KeySelector keySelector) {
Preconditions.checkNotNull(keySelector);
final TypeInformation otherKey = TypeExtractor.getKeySelectorTypes(keySelector, input2.getType());
return equalTo(keySelector, otherKey);
}
public EqualTo equalTo(KeySelector keySelector, TypeInformation keyType) {
Preconditions.checkNotNull(keySelector);
Preconditions.checkNotNull(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));
}
//......
} - Where对象提供了equalTo操作，用于指定input2的keySelector，它创建并返回EqualTo对象
EqualTo
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java
@Public
public class EqualTo {
private final KeySelector keySelector2;
EqualTo(KeySelector keySelector2) {
this.keySelector2 = requireNonNull(keySelector2);
}
@PublicEvolving
public WithWindow window(WindowAssigner, W> assigner) {
return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType, assigner, null, null, null);
}
} - EqualTo对象提供了window操作，它创建并返回WithWindow对象
WithWindow
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java
@Public
public static class WithWindow {
private final DataStream input1;
private final DataStream input2;
private final KeySelector keySelector1;
private final KeySelector keySelector2;
private final TypeInformation keyType;
private final WindowAssigner, W> windowAssigner;
private final Trigger, ? super W> trigger;
private final Evictor, ? super W> evictor;
private final Time allowedLateness;
private WindowedStream, KEY, W> windowedStream;
protected WithWindow(DataStream input1,
DataStream input2,
KeySelector keySelector1,
KeySelector keySelector2,
TypeInformation keyType,
WindowAssigner, W> windowAssigner,
Trigger, ? super W> trigger,
Evictor, ? 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 trigger(Trigger, ? super W> newTrigger) {
return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
windowAssigner, newTrigger, evictor, allowedLateness);
}
@PublicEvolving
public WithWindow evictor(Evictor, ? super W> newEvictor) {
return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
windowAssigner, trigger, newEvictor, allowedLateness);
}
@PublicEvolving
public WithWindow allowedLateness(Time newLateness) {
return new WithWindow<>(input1, input2, keySelector1, keySelector2, keyType,
windowAssigner, trigger, evictor, newLateness);
}
public DataStream apply(CoGroupFunction function) {
TypeInformation resultType = TypeExtractor.getCoGroupReturnTypes(
function,
input1.getType(),
input2.getType(),
"CoGroup",
false);
return apply(function, resultType);
}
@PublicEvolving
@Deprecated
public SingleOutputStreamOperator with(CoGroupFunction function) {
return (SingleOutputStreamOperator) apply(function);
}
public DataStream apply(CoGroupFunction function, TypeInformation resultType) {
//clean the closure
function = input1.getExecutionEnvironment().clean(function);
UnionTypeInfo unionType = new UnionTypeInfo<>(input1.getType(), input2.getType());
UnionKeySelector unionKeySelector = new UnionKeySelector<>(keySelector1, keySelector2);
DataStream> taggedInput1 = input1
.map(new Input1Tagger())
.setParallelism(input1.getParallelism())
.returns(unionType);
DataStream> taggedInput2 = input2
.map(new Input2Tagger())
.setParallelism(input2.getParallelism())
.returns(unionType);
DataStream> unionStream = taggedInput1.union(taggedInput2);
// we explicitly create the keyed stream to manually pass the key type information in
windowedStream =
new KeyedStream, 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(function), resultType);
}
@PublicEvolving
@Deprecated
public SingleOutputStreamOperator with(CoGroupFunction function, TypeInformation resultType) {
return (SingleOutputStreamOperator) apply(function, resultType);
}
@VisibleForTesting
Time getAllowedLateness() {
return allowedLateness;
}
@VisibleForTesting
WindowedStream, KEY, W> getWindowedStream() {
return windowedStream;
}
} - WithWindow可以设置windowAssigner、trigger、evictor、allowedLateness，它提供apply操作(
with操作被标记为废弃) - apply操作接收CoGroupFunction，它内部是先根据两个keySelector创建UnionKeySelector，然后对两个input stream分别使用Input1Tagger及Input2Tagger进行map转换为TaggedUnion对象的stream，然后执行taggedInput1.union(taggedInput2)得到unionStream，之后使用UnionKeySelector将unionStream转换为KeyedStream，之后在对KeyedStream执行window操作，把原来的windowAssigner、trigger、evictor、allowedLateness都赋值过去，最后将用户定义的CoGroupFunction包装为CoGroupWindowFunction，然后调用windowedStream.apply方法
- 可以看到apply操作内部转化的WindowedStream，其element类型为TaggedUnion；WindowedStream使用的KeyedStream，它的KeySelector为UnionKeySelector；而KeyedStream是基于TaggedUnion类型的DataStream，是taggedInput1.union(taggedInput2)操作而来；而taggedInput1及taggedInput2是对原始input stream进行map操作而来，使用的MapFunction分别是Input1Tagger及Input2Tagger
CoGroupFunction
flink-core-1.7.0-sources.jar!/org/apache/flink/api/common/functions/CoGroupFunction.java
@Public
@FunctionalInterface
public interface CoGroupFunction extends Function, Serializable {
void coGroup(Iterable first, Iterable second, Collector out) throws Exception;
} - CoGroupFunction继承了Function，它定义了coGroup方法，该方法接收两个Iterable类型的element集合
Input1Tagger及Input2Tagger
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java
private static class Input1Tagger implements MapFunction> {
private static final long serialVersionUID = 1L;
@Override
public TaggedUnion map(T1 value) throws Exception {
return TaggedUnion.one(value);
}
}
private static class Input2Tagger implements MapFunction> {
private static final long serialVersionUID = 1L;
@Override
public TaggedUnion map(T2 value) throws Exception {
return TaggedUnion.two(value);
}
} - Input1Tagger及Input2Tagger实现了MapFunction，该map方法返回的类型为TaggedUnion
TaggedUnion
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java
@Internal
public static class TaggedUnion {
private final T1 one;
private final T2 two;
private TaggedUnion(T1 one, T2 two) {
this.one = one;
this.two = two;
}
public boolean isOne() {
return one != null;
}
public boolean isTwo() {
return two != null;
}
public T1 getOne() {
return one;
}
public T2 getTwo() {
return two;
}
public static TaggedUnion one(T1 one) {
return new TaggedUnion<>(one, null);
}
public static TaggedUnion two(T2 two) {
return new TaggedUnion<>(null, two);
}
} - TaggedUnion里头有one、two两个属性，它提供了两个静态工厂方法one及two，可以看到TaggedUnion对象要么one为null，要么two为null，不可能两个同时有值
UnionKeySelector
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java
private static class UnionKeySelector implements KeySelector, KEY> {
private static final long serialVersionUID = 1L;
private final KeySelector keySelector1;
private final KeySelector keySelector2;
public UnionKeySelector(KeySelector keySelector1,
KeySelector keySelector2) {
this.keySelector1 = keySelector1;
this.keySelector2 = keySelector2;
}
@Override
public KEY getKey(TaggedUnion value) throws Exception{
if (value.isOne()) {
return keySelector1.getKey(value.getOne());
} else {
return keySelector2.getKey(value.getTwo());
}
}
} - UnionKeySelector有两个KeySelector属性，它的getKey操作根据TaggedUnion来判断，如果是one，则使用keySelector1.getKey(value.getOne())，否则使用keySelector2.getKey(value.getTwo())
DataStream.union
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/DataStream.java
@Public
public class DataStream {
//......
@SafeVarargs
public final DataStream union(DataStream... streams) {
List> unionedTransforms = new ArrayList<>();
unionedTransforms.add(this.transformation);
for (DataStream newStream : streams) {
if (!getType().equals(newStream.getType())) {
throw new IllegalArgumentException("Cannot union streams of different types: "
+ getType() + " and " + newStream.getType());
}
unionedTransforms.add(newStream.getTransformation());
}
return new DataStream<>(this.environment, new UnionTransformation<>(unionedTransforms));
}
//......
} - DataStream的union操作，使用UnionTransformation创建了一个新的DataStream；注意union操作需要两个stream使用相同类型的element，这就是为什么WithWindow的apply操作对两个input stream分别使用Input1Tagger及Input2Tagger进行map转换为TaggedUnion对象来统一两个stream的element类型的原因
CoGroupWindowFunction
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java
private static class CoGroupWindowFunction
extends WrappingFunction>
implements WindowFunction, T, KEY, W> {
private static final long serialVersionUID = 1L;
public CoGroupWindowFunction(CoGroupFunction userFunction) {
super(userFunction);
}
@Override
public void apply(KEY key,
W window,
Iterable> values,
Collector out) throws Exception {
List oneValues = new ArrayList<>();
List twoValues = new ArrayList<>();
for (TaggedUnion val: values) {
if (val.isOne()) {
oneValues.add(val.getOne());
} else {
twoValues.add(val.getTwo());
}
}
wrappedFunction.coGroup(oneValues, twoValues, out);
}
} - CoGroupWindowFunction继承了WrappingFunction(
WrappingFunction继承了AbstractRichFunction，覆盖了父类的open、close、setRuntimeContext方法，用于管理wrappedFunction)，实现了WindowFunction接口，其apply方法对TaggedUnion类型的Iterable数据进行拆解，分别拆分到oneValues及twoValues中，然后调用用户定义的CoGroupFunction的coGroup方法
小结
- DataStream提供了coGroup方法，用于执行window coGroup操作，它返回的是CoGroupedStreams；CoGroupedStreams主要是提供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
- CoGroupedStreams的WithWindow对象的apply操作接收CoGroupFunction，它内部是先根据两个keySelector创建UnionKeySelector，然后对两个input stream分别使用Input1Tagger及Input2Tagger进行map转换为TaggedUnion对象的stream，然后执行taggedInput1.union(taggedInput2)得到unionStream，之后使用UnionKeySelector将unionStream转换为KeyedStream，之后在对KeyedStream执行window操作，把原来的windowAssigner、trigger、evictor、allowedLateness都赋值过去，最后将用户定义的CoGroupFunction包装为CoGroupWindowFunction，然后调用windowedStream.apply方法
- CoGroupedStreams的WithWindow对象的apply操作借助了DataStream的union操作类合并两个stream，然后转换为KeyedStream，这里关键的两个类分别是TaggedUnion及UnionKeySelector；TaggedUnion里头有one、two两个属性，它提供了两个静态工厂方法one及two，可以看到TaggedUnion对象要么one为null，要么two为null，不可能两个同时有值；UnionKeySelector有两个KeySelector属性，它的getKey操作根据TaggedUnion来判断，如果是one，则使用keySelector1.getKey(value.getOne())，否则使用keySelector2.getKey(value.getTwo())(
借助TaggedUnion类统一两个stream的element类型，然后好执行union操作) - CoGroupWindowFunction继承了WrappingFunction(
WrappingFunction继承了AbstractRichFunction，覆盖了父类的open、close、setRuntimeContext方法，用于管理wrappedFunction)，实现了WindowFunction接口，其apply方法对TaggedUnion类型的Iterable数据进行拆解，分别拆分到oneValues及twoValues中，然后调用用户定义的CoGroupFunction的coGroup方法 - CoGroupFunction继承了Function，它定义了coGroup方法，该方法接收两个Iterable类型的element集合；JoinedStreams的WithWindow对象的apply方法内部将JoinFunction或者FlatJoinFunction包装为CoGroupFunction(JoinFunction使用JoinCoGroupFunction包装，FlatJoinFunction使用FlatJoinCoGroupFunction包装)，然后去调用CoGroupedStreams的WithWindow的apply方法；而JoinCoGroupFunction及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JoinFunction或FlatJoinFunction的join方法(
这里的操作对集合为空的情况不做任何操作，因而实现的就是inner join效果；用户使用coGroup操作可以自定义CoGroupFunction实现outer join)
doc
- DataStream Transformations
- 聊聊flink DataStream的join操作
- Apache Flink using coGroup to achieve left-outer join