streamex

StreamEx 0.9.0

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

Full API documentation is available here.

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

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

StreamEx main points are the following:

• Shorter and convenient ways to do common tasks.
• Better interoperability with older code.
• 100% compatibility with the original JDK streams.
• Friendliness for parallel processing: any new feature takes advantage of parallel streams as much as possible.
• Performance and minimal overhead. Whenever StreamEx allows solving a task using less code compared to the standard JDK Stream API, 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"

Selecting stream elements of a specific type

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

Adding elements to a 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();
}

Removing unwanted elements and using a stream as an 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());
    }
}

Selecting map keys by value predicate:

Map<String, Role> nameToRole;

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

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();
}

Pairwise differences:

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

Support for byte/char/short/float types:

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

Define a 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));
}

And more!

License

This project is licensed under Apache License, version 2.0

Installation

Releases are available in Maven Central

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

Maven

Add this snippet to your project's pom.xml dependencies section:

<dependency>
  <groupId>one.util</groupId>
  <artifactId>streamex</artifactId>
  <version>0.9.0</version>
</dependency>

Gradle

Add this snippet to your project's build.gradle dependencies section:

implementation 'one.util:streamex:0.9.0'

Pull requests are welcome.