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本文主要研究一下flink KeyedStream的KeySelector
KeyedStream
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/KeyedStream.java
@Public
public class KeyedStream extends DataStream {
/**
* The key selector that can get the key by which the stream if partitioned from the elements.
*/
private final KeySelector keySelector;
/** The type of the key by which the stream is partitioned. */
private final TypeInformation keyType;
/**
* Creates a new {@link KeyedStream} using the given {@link KeySelector}
* to partition operator state by key.
*
* @param dataStream
* Base stream of data
* @param keySelector
* Function for determining state partitions
*/
public KeyedStream(DataStream dataStream, KeySelector keySelector) {
this(dataStream, keySelector, TypeExtractor.getKeySelectorTypes(keySelector, dataStream.getType()));
}
/**
* Creates a new {@link KeyedStream} using the given {@link KeySelector}
* to partition operator state by key.
*
* @param dataStream
* Base stream of data
* @param keySelector
* Function for determining state partitions
*/
public KeyedStream(DataStream dataStream, KeySelector keySelector, TypeInformation keyType) {
this(
dataStream,
new PartitionTransformation<>(
dataStream.getTransformation(),
new KeyGroupStreamPartitioner<>(keySelector, StreamGraphGenerator.DEFAULT_LOWER_BOUND_MAX_PARALLELISM)),
keySelector,
keyType);
}
/**
* Creates a new {@link KeyedStream} using the given {@link KeySelector} and {@link TypeInformation}
* to partition operator state by key, where the partitioning is defined by a {@link PartitionTransformation}.
*
* @param stream
* Base stream of data
* @param partitionTransformation
* Function that determines how the keys are distributed to downstream operator(s)
* @param keySelector
* Function to extract keys from the base stream
* @param keyType
* Defines the type of the extracted keys
*/
@Internal
KeyedStream(
DataStream stream,
PartitionTransformation partitionTransformation,
KeySelector keySelector,
TypeInformation keyType) {
super(stream.getExecutionEnvironment(), partitionTransformation);
this.keySelector = clean(keySelector);
this.keyType = validateKeyType(keyType);
}
//......
} - 这里可以看到KeyedStream的不同构造器中都需要一个KeySelector类型的参数
KeySelector
flink-core-1.7.0-sources.jar!/org/apache/flink/api/java/functions/KeySelector.java
@Public
@FunctionalInterface
public interface KeySelector extends Function, Serializable {
/**
* User-defined function that deterministically extracts the key from an object.
*
* For example for a class:
*
* public class Word {
* String word;
* int count;
* }
*
* The key extractor could return the word as
* a key to group all Word objects by the String they contain.
*
* The code would look like this
*
* public String getKey(Word w) {
* return w.word;
* }
*
*
* @param value The object to get the key from.
* @return The extracted key.
*
* @throws Exception Throwing an exception will cause the execution of the respective task to fail,
* and trigger recovery or cancellation of the program.
*/
KEY getKey(IN value) throws Exception;
} - KeySelector接口继承了Function接口，定义了getKey方法，用于从IN类型中提取出KEY
DataStream.keyBy
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/DataStream.java
/**
* It creates a new {@link KeyedStream} that uses the provided key for partitioning
* its operator states.
*
* @param key
* The KeySelector to be used for extracting the key for partitioning
* @return The {@link DataStream} with partitioned state (i.e. KeyedStream)
*/
public KeyedStream keyBy(KeySelector key) {
Preconditions.checkNotNull(key);
return new KeyedStream<>(this, clean(key));
}
/**
* It creates a new {@link KeyedStream} that uses the provided key with explicit type information
* for partitioning its operator states.
*
* @param key The KeySelector to be used for extracting the key for partitioning.
* @param keyType The type information describing the key type.
* @return The {@link DataStream} with partitioned state (i.e. KeyedStream)
*/
public KeyedStream keyBy(KeySelector key, TypeInformation keyType) {
Preconditions.checkNotNull(key);
Preconditions.checkNotNull(keyType);
return new KeyedStream<>(this, clean(key), keyType);
}
/**
* Partitions the operator state of a {@link DataStream} by the given key positions.
*
* @param fields
* The position of the fields on which the {@link DataStream}
* will be grouped.
* @return The {@link DataStream} with partitioned state (i.e. KeyedStream)
*/
public KeyedStream keyBy(int... fields) {
if (getType() instanceof BasicArrayTypeInfo || getType() instanceof PrimitiveArrayTypeInfo) {
return keyBy(KeySelectorUtil.getSelectorForArray(fields, getType()));
} else {
return keyBy(new Keys.ExpressionKeys<>(fields, getType()));
}
}
/**
* Partitions the operator state of a {@link DataStream} using field expressions.
* A field expression is either the name of a public field or a getter method with parentheses
* of the {@link DataStream}'s underlying type. A dot can be used to drill
* down into objects, as in {@code "field1.getInnerField2()" }.
*
* @param fields
* One or more field expressions on which the state of the {@link DataStream} operators will be
* partitioned.
* @return The {@link DataStream} with partitioned state (i.e. KeyedStream)
**/
public KeyedStream keyBy(String... fields) {
return keyBy(new Keys.ExpressionKeys<>(fields, getType()));
}
private KeyedStream keyBy(Keys keys) {
return new KeyedStream<>(this, clean(KeySelectorUtil.getSelectorForKeys(keys,
getType(), getExecutionConfig())));
} - DataStream的keyBy方法用于将DataStream转换为KeyedStream，该方法有不同的重载
- 一个是支持变长int数组，这个通常用于简单tuple类型，int为tuple的小标，从0开始，如果是多个int，表示是组合key，比如keyBy(0,1)表示要用tuple的第一个和第二个字段作为key；
- 一个是支持变长String数组，这个通常用于复杂tuple类型及POJO类型，对于POJO，String用于指定字段名，也支持对象/tuple嵌套属性，比如user.zip，对于对象类型的tuple，f0表示该tuple的第一个字段
- 一个是支持KeySelector，通过Key Selector Function可以自由指定key，比如从对象提取然后做些处理
- keyBy(int... fields)及keyBy(String... fields)里头均有调用到私有的keyBy(Keys
keys)方法，由于KeyedStream的构造器都需要KeySelector参数，所以该方法最后也是通过KeySelectorUtil.getSelectorForKeys将Keys转换为KeySelector对象
Keys.ExpressionKeys
flink-core-1.7.0-sources.jar!/org/apache/flink/api/common/operators/Keys.java
/**
* Represents (nested) field access through string and integer-based keys
*/
public static class ExpressionKeys extends Keys {
public static final String SELECT_ALL_CHAR = "*";
public static final String SELECT_ALL_CHAR_SCALA = "_";
private static final Pattern WILD_CARD_REGEX = Pattern.compile("[\\.]?("
+ "\\" + SELECT_ALL_CHAR + "|"
+ "\\" + SELECT_ALL_CHAR_SCALA +")$");
// Flattened fields representing keys fields
private List keyFields;
private TypeInformation[] originalKeyTypes;
//......
/**
* Create String-based (nested) field expression keys on a composite type.
*/
public ExpressionKeys(String[] keyExpressions, TypeInformation type) {
checkNotNull(keyExpressions, "Field expression cannot be null.");
this.keyFields = new ArrayList<>(keyExpressions.length);
if (type instanceof CompositeType){
CompositeType cType = (CompositeType) type;
this.originalKeyTypes = new TypeInformation[keyExpressions.length];
// extract the keys on their flat position
for (int i = 0; i < keyExpressions.length; i++) {
String keyExpr = keyExpressions[i];
if (keyExpr == null) {
throw new InvalidProgramException("Expression key may not be null.");
}
// strip off whitespace
keyExpr = keyExpr.trim();
List flatFields = cType.getFlatFields(keyExpr);
if (flatFields.size() == 0) {
throw new InvalidProgramException("Unable to extract key from expression '" + keyExpr + "' on key " + cType);
}
// check if all nested fields can be used as keys
for (FlatFieldDescriptor field : flatFields) {
if (!field.getType().isKeyType()) {
throw new InvalidProgramException("This type (" + field.getType() + ") cannot be used as key.");
}
}
// add flat fields to key fields
keyFields.addAll(flatFields);
String strippedKeyExpr = WILD_CARD_REGEX.matcher(keyExpr).replaceAll("");
if (strippedKeyExpr.isEmpty()) {
this.originalKeyTypes[i] = type;
} else {
this.originalKeyTypes[i] = cType.getTypeAt(strippedKeyExpr);
}
}
}
else {
if (!type.isKeyType()) {
throw new InvalidProgramException("This type (" + type + ") cannot be used as key.");
}
// check that all key expressions are valid
for (String keyExpr : keyExpressions) {
if (keyExpr == null) {
throw new InvalidProgramException("Expression key may not be null.");
}
// strip off whitespace
keyExpr = keyExpr.trim();
// check that full type is addressed
if (!(SELECT_ALL_CHAR.equals(keyExpr) || SELECT_ALL_CHAR_SCALA.equals(keyExpr))) {
throw new InvalidProgramException(
"Field expression must be equal to '" + SELECT_ALL_CHAR + "' or '" + SELECT_ALL_CHAR_SCALA + "' for non-composite types.");
}
// add full type as key
keyFields.add(new FlatFieldDescriptor(0, type));
}
this.originalKeyTypes = new TypeInformation[] {type};
}
}
//......
} - ExpressionKeys是Keys里头的一个静态类，它继承了Keys对象；keyBy(int... fields)及keyBy(String... fields)里头均有通过new Keys.ExpressionKeys，将fields转换为Keys.ExpressionKeys，最后调用私有的keyBy(Keys
keys)方法
KeySelectorUtil.getSelectorForKeys
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/util/keys/KeySelectorUtil.java
@Internal
public final class KeySelectorUtil {
public static KeySelector getSelectorForKeys(Keys keys, TypeInformation typeInfo, ExecutionConfig executionConfig) {
if (!(typeInfo instanceof CompositeType)) {
throw new InvalidTypesException(
"This key operation requires a composite type such as Tuples, POJOs, or Case Classes.");
}
CompositeType compositeType = (CompositeType) typeInfo;
int[] logicalKeyPositions = keys.computeLogicalKeyPositions();
int numKeyFields = logicalKeyPositions.length;
TypeInformation[] typeInfos = keys.getKeyFieldTypes();
// use ascending order here, the code paths for that are usually a slight bit faster
boolean[] orders = new boolean[numKeyFields];
for (int i = 0; i < numKeyFields; i++) {
orders[i] = true;
}
TypeComparator comparator = compositeType.createComparator(logicalKeyPositions, orders, 0, executionConfig);
return new ComparableKeySelector<>(comparator, numKeyFields, new TupleTypeInfo<>(typeInfos));
}
//......
} - KeySelectorUtil.getSelectorForKeys方法用于将Keys转换为KeySelector类型
小结
- KeyedStream的不同构造器中都需要一个KeySelector参数
- DataStream的keyBy方法有不同的重载，支持变长int数组，变长String数组以及KeySelector类型
- keyBy(int... fields)及keyBy(String... fields)里头均有通过new Keys.ExpressionKeys，将fields转换为Keys.ExpressionKeys，最后调用私有的keyBy(Keys
keys)方法，该方法通过调用KeySelectorUtil.getSelectorForKeys方法将Keys转换为KeySelector类型
doc
- Specifying Keys