Enhancing Java 8 Streams.

This library defines four classes: StreamEx, IntStreamEx, LongStreamEx, DoubleStreamEx which are fully compatible with Java 8 stream classes and provide many additional useful methods. Also EntryStream class is provided which represents the stream of map entries and provides additional functionality for this case. Finally there are some new useful collectors defined in MoreCollectors class as well as primitive collectors concept.

Full API documentation is available here.

Take a look at the Cheatsheet for brief introduction to the StreamEx!

Before updating StreamEx check the migration notes and full list of changes.

StreamEx library main points are following:

  • Shorter and convenient ways to do the common tasks.
  • Better interoperability with older code.
  • 100% compatibility with original JDK streams.
  • Friendliness for parallel processing: any new feature takes the advantage on parallel streams as much as possible.
  • Performance and minimal overhead. If StreamEx allows to solve the task using less code compared to standard Stream, it should not be significantly slower than the standard way (and sometimes it’s even faster).

Examples

Collector shortcut methods (toList, toSet, groupingBy, joining, etc.)

List<String> userNames = StreamEx.of(users).map(User: :getName).toList();
Map<Role.List<User>> role2users = StreamEx.of(users).groupingBy(User: :getRole);
StreamEx.of(1.2.3).joining("; "); // "1; 2; 3"Copy the code

Selecting stream elements of specific type

public List<Element> elementsOf(NodeList nodeList) {
    return IntStreamEx.range(nodeList.getLength())
      .mapToObj(nodeList: :item).select(Element.class).toList();
}Copy the code

Adding elements to stream

public List<String> getDropDownOptions() {
    return StreamEx.of(users).map(User: :getName).prepend("(none)").toList();
}

public int[] addValue(int[] arr, int value) {
    return IntStreamEx.of(arr).append(value).toArray();
}Copy the code

Removing unwanted elements and using the stream as Iterable:

public void copyNonEmptyLines(Reader reader, Writer writer) throws IOException {
    for(String line : StreamEx.ofLines(reader).remove(String: :isEmpty)) {
        writer.write(line);
        writer.write(System.lineSeparator()); }}Copy the code

Selecting map keys by value predicate:

Map<String.Role> nameToRole;

public Set<String> getEnabledRoleNames() {
    return StreamEx.ofKeys(nameToRole, Role: :isEnabled).toSet();
}Copy the code

Operating on key-value pairs:

public Map<String.List<String>> invert(Map<String.List<String>> map) {
    return EntryStream.of(map).flatMapValues(List: :stream).invert().grouping();
}

public Map<String.String> stringMap(Map<Object.Object> map) {
    return EntryStream.of(map).mapKeys(String: :valueOf)
        .mapValues(String: :valueOf).toMap();
}

Map<String.Group> nameToGroup;

public Map<String.List<User>> getGroupMembers(Collection<String> groupNames) {
    return StreamEx.of(groupNames).mapToEntry(nameToGroup: :get)
        .nonNullValues().mapValues(Group: :getMembers).toMap();
}Copy the code

Pairwise differences:

DoubleStreamEx.of(input).pairMap((a, b) -> b-a).toArray();Copy the code

Support of byte/char/short/float types:

short[] multiply(short[] src, short multiplier) {
    return IntStreamEx.of(src).map(x -> x*multiplier).toShortArray(); 
}Copy the code

Define custom lazy intermediate operation recursively:

static <T> StreamEx<T> scanLeft(StreamEx<T> input, BinaryOperator<T> operator) {
        return input.headTail((head, tail) -> scanLeft(tail.mapFirst(cur -> operator.apply(head, cur)), operator)
                .prepend(head));
}Copy the code

And more!

Installation

Releases are available in Maven Central

Before updating StreamEx check the migration notes and full list of changes.

To use from maven add this snippet to the pom.xml dependencies section:

<dependency>
  <groupId>one.util</groupId>
  <artifactId>streamex</artifactId>
  <version< / a > 0.6.5version>
</dependency>Copy the code

Pull requests are welcome.