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!
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 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.