Package com.yahoo.stream

Class CustomCollectors

java.lang.Object

com.yahoo.stream.CustomCollectors

public class CustomCollectors
extends Object

The purpose of this class is to fill gaps in the Java Collectors api by offering convenient ways to retrieve implementations of Collector.

For example, to get a collector that accumulates elements into a map with predictable iteration order:

     Map<String, Person> idToPerson =
         persons.stream().collect(toLinkedMap(Person::id, Functions.identity());
 

Author:

gjoranv

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	CustomCollectors.DuplicateKeyException

Method Summary

Modifier and Type	Method	Description
static <T> Collector<T,?,Optional<T>>	singleton()	Returns a Collector that returns a singleton, or throws an IllegalArgumentException if there are more than one item.
static <T, K, U, M extends Map<K, U>> Collector<T,?,M>	toCustomMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper, Supplier<M> mapSupplier)	Returns a Collector that accumulates elements into a Map created by the given supplier.
static <T, K, U> Collector<T,?,Map<K,U>>	toLinkedMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper)	Returns a Collector that accumulates elements into a Map that provides insertion order iteration.

Methods inherited from class java.lang.Object

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

Method Details

toLinkedMap

public static <T,
K,
U> Collector<T,?,Map<K,U>> toLinkedMap(Function<? super T,? extends K> keyMapper,
 Function<? super T,? extends U> valueMapper)

Returns a Collector that accumulates elements into a Map that provides insertion order iteration. This a convenience that can be used instead of calling Collectors.toMap(Function, Function, BinaryOperator, Supplier). with a merger that throws upon duplicate keys.

Type Parameters:

T - Type of the input elements.

K - Output type of the key mapping function.

U - Output type of the value mapping function.

Parameters:

keyMapper - Mapping function to produce keys.

valueMapper - Mapping function to produce values.

Returns:

A collector which collects elements into a map with insertion order iteration.

Throws:

CustomCollectors.DuplicateKeyException - If two elements map to the same key.

toCustomMap

public static <T,
K,
U,
M extends Map<K,
U>>
Collector<T,?,M> toCustomMap(Function<? super T,? extends K> keyMapper,
 Function<? super T,? extends U> valueMapper,
 Supplier<M> mapSupplier)

Returns a Collector that accumulates elements into a Map created by the given supplier. This a convenience that can be used instead of calling Collectors.toMap(Function, Function, BinaryOperator, Supplier). with a merger that throws upon duplicate keys.

Type Parameters:

T - Type of the input elements.

K - Output type of the key mapping function.

U - Output type of the value mapping function.

M - Type of the resulting map.

Parameters:

keyMapper - Mapping function to produce keys.

valueMapper - Mapping function to produce values.

mapSupplier - Supplier of a new map.

Returns:

A collector which collects elements into a map created by the given supplier.

Throws:

CustomCollectors.DuplicateKeyException - If two elements map to the same key.

singleton

public static <T> Collector<T,?,Optional<T>> singleton()

Returns a Collector that returns a singleton, or throws an IllegalArgumentException if there are more than one item.

Type Parameters:

T - Type of the input elements.

Returns:

A collector returning an optional element

Throws:

IllegalArgumentException - if there are more than one element