Enhancing Java Stream API
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:
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!
This project is licensed under Apache License, version 2.0
Releases are available in Maven Central
Before updating StreamEx check the migration notes and the full list of changes.
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>Add this snippet to your project's build.gradle dependencies section:
implementation 'one.util:streamex:0.9.0'Pull requests are welcome.
No open issues yet, or sync has not completed.