Package org.mycore.common

Class MCRStreamUtils

java.lang.Object

org.mycore.common.MCRStreamUtils

public class MCRStreamUtils
extends Object

Helper methods to handle common Stream use cases.

Author:

Thomas Scheffler (yagee)

Constructor Summary

Constructors

Constructor	Description
MCRStreamUtils()

Method Summary

Modifier and Type	Method	Description
static <T> Stream<T>	asStream(Enumeration<T> e)	Transforms an Enumeration in a Stream.
static <T> Stream<T>	concat(Stream<T>... streams)	Concats any number of Streams not just 2 as in Stream.concat(Stream, Stream).
static <T> Predicate<T>	distinctByKey(Function<? super T,?> keyExtractor)	Stream distinct by filter function.
static <T> Stream<T>	flatten(T node, Function<T,Collection<T>> subNodeSupplier, Function<Collection<T>,Stream<T>> streamProvider)	Short circuit for calling flatten(node, subNodeSupplier, subNodeSupplier, t -> true)
static <T> Stream<T>	flatten(T node, Function<T,Collection<T>> subNodeSupplier, Function<Collection<T>,Stream<T>> streamProvider, Predicate<T> filter)	Example:
static <T> Predicate<T>	not(Predicate<T> predicate)	Negates a predicate.

Methods inherited from class java.lang.Object

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

Constructor Details

MCRStreamUtils

public MCRStreamUtils()

Method Details

flatten

public static <T> Stream<T> flatten(T node,
 Function<T,Collection<T>> subNodeSupplier,
 Function<Collection<T>,Stream<T>> streamProvider)

Short circuit for calling flatten(node, subNodeSupplier, subNodeSupplier, t -> true)

Parameters:

node - node that holds kind-of subtree.

subNodeSupplier - a function that delivers subtree items of next level

streamProvider - a function that makes a Stream of a Collection<T>, usually Collection::stream or Collection::parallelStream

Since:

2016.04

See Also:

• flatten(Object, Function, Function, Predicate)

flatten

public static <T> Stream<T> flatten(T node,
 Function<T,Collection<T>> subNodeSupplier,
 Function<Collection<T>,Stream<T>> streamProvider,
 Predicate<T> filter)

Example:

   MCRCategory foo = MCRCategoryDAOFactory.getInstance().getCategory(MCRCategoryID.rootID("foo"), -1);
   Stream<MCRCategory> parentCategories = flatten(foo, MCRCategory::getChildren, true, MCRCategory::hasChildren);
 

Parameters:

node - first node the stream is made of

subNodeSupplier - a function that delivers subtree items of next level

streamProvider - a function that makes a Stream of a Collection<T>, usually Collection::stream or Collection::parallelStream

filter - a predicate that filters the element of the next level

Since:

2016.04

asStream

public static <T> Stream<T> asStream(Enumeration<T> e)

Transforms an Enumeration in a Stream.

Parameters:

e - the enumeration to transform

Returns:

a sequential, ordered Stream of unknown size

concat

@SafeVarargs
public static <T> Stream<T> concat(Stream<T>... streams)

Concats any number of Streams not just 2 as in Stream.concat(Stream, Stream).

Since:

2016.04

distinctByKey

public static <T> Predicate<T> distinctByKey(Function<? super T,?> keyExtractor)

Stream distinct by filter function.

persons.stream().filter(MCRStreamUtils.distinctByKey(p -> p.getName());

It should be noted that for ordered parallel stream this solution does not guarantee which object will be extracted (unlike normal distinct()).

Parameters:

keyExtractor - a compare function

Returns:

a predicate

See Also:

• stackoverflow

not

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

Negates a predicate.

Parameters:

predicate - the predicate to negate

Returns:

the negated predicate

See Also:

• stackoverflow