mbryzhko/stream-utils

A collection of utilities for Java 8 Streams

com.conductor.stream.utils

This repo contains common utilities for dealing with streams. It is intended to be very light weight, and has no external dependencies.

Usage

These utilities are published to maven central. To use them, simply add the following dependency:

<dependency>
    <groupId>com.conductor</groupId>
    <artifactId>stream-utils</artifactId>
    <version>${LATEST_VERSION}</version>
</dependency>

Utilities

For convenience, there are static functions around all of the useful utilities in this repo. Here are the utilities currently supported:

StreamUtils

These are a series of utilities that can be used on any stream.

StreamUtils.buffer

Takes a stream, and chunks it up by a given size.

Sample Usage

Stream<List<Integer>> chunkedStream = StreamUtils.buffer(Stream.of(1, 2, 3, 4), 2);
assertEquals(chunkedStream, Stream.of(Arrays.asList(1, 2), Arrays.asList(3, 4));

StreamUtils.noCombiner

A convenience lambda for a Stream Collector that doesn't allow the combine method to be called.

Sample Usage

String combined = Stream.of(1, 2, 3)
    .collect(
        StringBuilder::new,
        StringBuilder::append,
        StreamUtils.noCombiner()
    ).toString();
assertEquals("123", combined);

StreamUtils.switchIfEmpty

Takes in a stream, and a supplier for an alternate stream to be used if the given stream is empty.

Sample Usage

Stream<Integer> stream = StreamUtils.switchIfEmpty(Stream.empty(), () -> Stream.of(1, 2, 3));
assertEquals(stream, Stream.of(1, 2, 3));

OrderedStreamUtils

These are a series of utilities that can be used on an ordered stream.

OrderedStreamUtils.groupBy

Takes a stream, and chunks it up by a given key, obtained by the inputted function. Assumes the stream is ordered by that key.

Sample Usage

Stream<List<Integer>> groupedStream = OrderedStreamUtils.groupBy(Stream.of(1, 3, 5, 2, 4), (i) -> i % 2);
assertEquals(groupedStream, Stream.of(Arrays.asList(1, 3, 5), Arrays.asList(2, 4));

OrderedStreamUtils.aggregate

Takes a stream, and chunks it up by a given key, obtained by the inputted function. Assumes the stream is ordered by that key. It then takes the list, and transforms it into an object, given the provided aggregation function.

Sample Usage

Stream<String> aggregatedStream = OrderedStreamUtils.aggregate(
    Stream.of(1, 3, 5, 2, 4),
    (i) -> i % 2,
    List::toString
);
assertEquals(aggregatedStream, Stream.of(Arrays.asList(1, 3, 5).toString(), Arrays.asList(2, 4).toString());

OrderedStreamUtils.sortedMerge

Takes a collection of streams, and merges them together, using either the provided comparator function, or the natural ordering of the items.

Sample Usage

Stream<Integer> mergedStream = OrderedStreamUtils.sortedMerge(Arrays.asList(
    Stream.of(1, 4, 7),
    Stream.of(2, 5, 8),
    Stream.of(3, 6, 9)
));
assertEquals(mergedStream, Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9);

or

Stream<Integer> mergedStream = OrderedStreamUtils.sortedMerge(Arrays.asList(
    Stream.of(1, 4, 7),
    Stream.of(2, 5, 8),
    Stream.of(3, 6, 9)
), Comparators.<Integer>naturalOrder().reversed());
assertEquals(mergedStream, Stream.of(3, 2, 1, 6, 5, 4, 9, 8, 7);

OrderedStreamUtils.join

Takes in two sorted streams, and joins them together, using the provided keying functions and comparator to determine order, the given join function to merge the two items, and the join type desired (full, inner, and left).

Sample Usage

Stream<Integer> joinedStream = OrderedStreamUtils.join(
        Stream.of(1, 2, 3),
        Stream.of(1, 2, 3),
        Comparator.naturalOrder(),
        Function.identity(),
        Function.identity(),
        (num1, num2) -> num1 + num2,
        JoinType.OUTER
);
assertEquals(joinedStream, Stream.of(2, 4, 6));

There is also a builder for convenience.

Stream<Integer> joinedStream = OrderedStreamUtils.join(JoinBuilder.builder()
        .setLeftHandSide(Stream.of(1, 2, 3))
        .setRightHandSide(Stream.of(1, 2, 3))
        .setOrdering(Comparator.naturalOrder())
        .setLeftHandKeyingFunction(Function.identity())
        .setRightHandKeyingFunction(Function.identity())
        .setJoinFunction((num1, num2) -> num1 + num2)
        .setJoinType(JoinType.OUTER)
);
assertEquals(joinedStream, Stream.of(2, 4, 6));