com.yahoo.bard.webservice.util

Class StreamUtils

java.lang.Object

com.yahoo.bard.webservice.util.StreamUtils

public class StreamUtils
extends Object

Utils for dealing with streams.

Constructor Summary

Constructors

Constructor and Description
StreamUtils()

Method Summary

Modifier and Type	Method and Description
static <T> Set<T>	append(Set<T> set, T value) Copy a set, add a value to it and return the new set.
static <T> Predicate<T>	not(Predicate<T> predicate) Negate the given predicate.
static <T> Set<T>	setMerge(Set<T> a, Set<T> b) Merge two sets without modifying either.
static <T> BinaryOperator<T>	throwingMerger() Returns a merge function, suitable for use in Map.merge() or toMap(), which always throws IllegalStateException.
static <S,K,M extends Map<K,S>> Collector<S,?,M>	toDictionary(Function<? super S,? extends K> keyMapper, Supplier<M> mapSupplier) Return a collector that creates a dictionary using the given key function and the given map supplier.
static <S,K> Collector<S,?,LinkedHashMap<K,S>>	toLinkedDictionary(Function<? super S,? extends K> keyMapper) Return a collector that creates a LinkedHashMap dictionary using the given key function.
static <S,K,V> Collector<S,?,LinkedHashMap<K,V>>	toLinkedMap(Function<? super S,? extends K> keyMapper, Function<? super S,? extends V> valueMapper) Return a collector that creates a LinkedHashMap using the given key and value functions.
static <S,K,V,M extends Map<K,V>> Collector<S,?,M>	toMap(Function<? super S,? extends K> keyMapper, Function<? super S,? extends V> valueMapper, Supplier<M> mapSupplier) Return a collector that creates a Map using the given key and value functions.
static <T> Set<T>	toUnmodifiableSet(Stream<T> values) Collect a stream into an unmodifiable set preserving first-in ordering.
static <T,R> Function<T,R>	uncheckedCast(Class<R> targetType) Return a function that can be used to do unchecked casts without generating a compiler warning.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

StreamUtils

public StreamUtils()

Method Detail

throwingMerger

public static <T> BinaryOperator<T> throwingMerger()

Returns a merge function, suitable for use in Map.merge() or toMap(), which always throws IllegalStateException. This can be used to enforce the assumption that the elements being collected are distinct.

Type Parameters:

T - the type of input arguments to the merge function

Returns:

a merge function which always throw IllegalStateException

See Also:

Collectors.throwingMerger()

toLinkedMap

public static <S,K,V> Collector<S,?,LinkedHashMap<K,V>> toLinkedMap(Function<? super S,? extends K> keyMapper,
                                                                    Function<? super S,? extends V> valueMapper)

Return a collector that creates a LinkedHashMap using the given key and value functions. This collector assumes the elements being collected are distinct.

Type Parameters:

S - Type of the objects being collected

K - Type of the keys

V - Type of the values

Parameters:

keyMapper - Mapping function for the key

valueMapper - Mapping function for the value

Returns:

a collector that creates a LinkedHashMap using the given key and value functions.

Throws:

IllegalStateException - if multiple values are associated with the same key

See Also:

Collectors.toMap(Function, Function, BinaryOperator, java.util.function.Supplier)

toMap

public static <S,K,V,M extends Map<K,V>> Collector<S,?,M> toMap(Function<? super S,? extends K> keyMapper,
                                                                Function<? super S,? extends V> valueMapper,
                                                                Supplier<M> mapSupplier)

Return a collector that creates a Map using the given key and value functions. This collector assumes the elements being collected are distinct.

The concrete type of the Map being created is given by a Supplier.

Type Parameters:

S - Type of the objects being collected

K - Type of the keys

V - Type of the values

M - The type of Map being collected into

Parameters:

keyMapper - Mapping function for the key

valueMapper - Mapping function for the value

mapSupplier - A Supplier which provides a new, empty Map into which the results will be inserted

Returns:

a collector that creates a Map using the given key and value functions

Throws:

IllegalStateException - if multiple values are associated with the same key

See Also:

Collectors.toMap(Function, Function, BinaryOperator, java.util.function.Supplier)

toLinkedDictionary

public static <S,K> Collector<S,?,LinkedHashMap<K,S>> toLinkedDictionary(Function<? super S,? extends K> keyMapper)

Return a collector that creates a LinkedHashMap dictionary using the given key function. This collector assumes the elements being collected are distinct.

Type Parameters:

S - Type of the objects being collected and the values of the dictionary / map

K - Type of the keys

Parameters:

keyMapper - Mapping function for the key

Returns:

a collector that creates a LinkedHashMap dictionary using the given key function.

Throws:

IllegalStateException - if multiple values are associated with the same key

See Also:

Collectors.toMap(Function, Function, BinaryOperator, java.util.function.Supplier)

toDictionary

public static <S,K,M extends Map<K,S>> Collector<S,?,M> toDictionary(Function<? super S,? extends K> keyMapper,
                                                                     Supplier<M> mapSupplier)

Return a collector that creates a dictionary using the given key function and the given map supplier. This collector assumes the elements being collected are distinct.

Type Parameters:

S - Type of the objects being collected and the values of the dictionary / map

K - Type of the keys

M - The type of Map being collected into

Parameters:

keyMapper - Mapping function for the key

mapSupplier - A Supplier which provides a new, empty Map into which the results will be inserted

Returns:

a Collector that creates a dictionary using the given key function and the given map supplier

Throws:

IllegalStateException - if multiple values are associated with the same key

See Also:

Collectors.toMap(Function, Function, BinaryOperator, java.util.function.Supplier)

toUnmodifiableSet

public static <T> Set<T> toUnmodifiableSet(Stream<T> values)

Collect a stream into an unmodifiable set preserving first-in ordering.

Type Parameters:

T - The type of the value stream

Parameters:

values - The stream of values to be collected

Returns:

An unmodifiable copy of a linked hash set view of the stream

not

public static <T> Predicate<T> not(Predicate<T> predicate)

Negate the given predicate.

Type Parameters:

T - Type of the predicate being negated

Parameters:

predicate - Predicate to negate

Returns:

the negated predicate

uncheckedCast

public static <T,R> Function<T,R> uncheckedCast(Class<R> targetType)

Return a function that can be used to do unchecked casts without generating a compiler warning.

Essentially the same as annotating the cast with @SuppressWarnings("unchecked"), which you can't do inside a stream.

Type Parameters:

T - Operand type (type of function parameter)

R - Cast type

Parameters:

targetType - Class to cast the operand (function parameter) to. Used only to set the generic type

Returns:

The function that will do the cast

append

public static <T> Set<T> append(Set<T> set,
                                T value)

Copy a set, add a value to it and return the new set.

Type Parameters:

T - The type of the set

Parameters:

set - The original set being copied.

value - The value being appended to the set.

Returns:

the new set containing the additional value

setMerge

public static <T> Set<T> setMerge(Set<T> a,
                                  Set<T> b)

Merge two sets without modifying either. This method implements BinaryOperator for use in stream reductions.

Type Parameters:

T - The type of the underlying sets

Parameters:

a - One input set

b - Another input set

Returns:

A new set containing the values of the original sets