/**
*
* Copyright (c) 2006-2017, Speedment, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License"); You may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.speedment.runtime.core.util;
import com.speedment.common.mapstream.MapStream;
import java.util.*;
import java.util.function.*;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import static com.speedment.common.invariant.NullUtil.requireNonNullElements;
import static com.speedment.runtime.core.util.StaticClassUtil.instanceNotAllowed;
import static java.util.Objects.requireNonNull;
/**
* Utility methods for collecting Speedment streams in various ways.
*
* @author Per Minborg
* @author Emil Forslund
* @since 2.1.0
*/
public final class CollectorUtil {
private static final String NULL_TEXT = " must not be null";
@SafeVarargs
@SuppressWarnings({"unchecked", "varargs"})
public static <T> T of(Supplier<T> supplier, Consumer<T> modifier, Consumer<T>... additionalModifiers) {
requireNonNull(supplier, "supplier" + NULL_TEXT);
requireNonNull(modifier, "modifier" + NULL_TEXT);
requireNonNullElements(additionalModifiers, "additionalModifiers" + NULL_TEXT);
final T result = supplier.get();
modifier.accept(result);
Stream.of(additionalModifiers).forEach((Consumer<T> c) -> {
c.accept(result);
});
return result;
}
public static <I, T> T of(Supplier<I> supplier, Consumer<I> modifier, Function<I, T> finisher) {
Objects.requireNonNull(supplier, "supplier" + NULL_TEXT);
Objects.requireNonNull(modifier, "modifier" + NULL_TEXT);
Objects.requireNonNull(finisher, "finisher" + NULL_TEXT);
final I intermediateResult = supplier.get();
modifier.accept(intermediateResult);
return finisher.apply(intermediateResult);
}
public static <T> Collector<T, Set<T>, Set<T>> toUnmodifiableSet() {
return Collector.of(HashSet::new, Set::add, (left, right) -> {
left.addAll(right);
return left;
}, Collections::unmodifiableSet, Collector.Characteristics.UNORDERED);
}
public static <T> Collector<T, ?, List<T>> toReversedList() {
return Collectors.collectingAndThen(Collectors.toList(), l -> {
Collections.<T>reverse(l);
return l;
});
}
@SafeVarargs
@SuppressWarnings({"unchecked", "varargs"})
public static <T> Set<T> unmodifiableSetOf(T... items) {
requireNonNullElements(items);
return Stream.of(items).collect(toUnmodifiableSet());
}
/**
* Similar to the
* {@link java.util.stream.Collectors#joining(java.lang.CharSequence, java.lang.CharSequence, java.lang.CharSequence) }
* method except that this method surrounds the result with the specified
* {@code prefix} and {@code suffix} even if the stream is empty.
*
* @param delimiter the delimiter to separate the strings
* @param prefix the prefix to put before the result
* @param suffix the suffix to put after the result
* @return a collector for joining string elements
*/
public static Collector<String, ?, String> joinIfNotEmpty(String delimiter, String prefix, String suffix) {
return new CollectorImpl<>(
() -> new StringJoiner(delimiter),
StringJoiner::add,
StringJoiner::merge,
s -> s.length() > 0
? prefix + s + suffix
: s.toString(),
Collections.emptySet()
);
}
/**
* Returns the specified string wrapped as an Optional. If the string was
* null or empty, the Optional will be empty.
*
* @param str the string to wrap
* @return the string wrapped as an optional
*/
public static Optional<String> ifEmpty(String str) {
return Optional.ofNullable(str).filter(s -> !s.isEmpty());
}
/**
* Returns a new {@link MapStream} where the elements have been grouped
* together using the specified function.
*
* @param <T> the stream element type
* @param <C> the type of the key to group by
* @param grouper the function to use for grouping
* @return a {@link MapStream} grouped by key
*/
public static <T, C> Collector<T, ?, MapStream<C, List<T>>> groupBy(Function<T, C> grouper) {
return new CollectorImpl<>(
() -> new GroupHolder<>(grouper),
GroupHolder::add,
GroupHolder::merge,
GroupHolder::finisher,
Collections.emptySet()
);
}
private static class GroupHolder<C, T> {
private final Function<T, C> grouper;
private final Map<C, List<T>> elements;
private final Function<C, List<T>> createList = c -> new ArrayList<>();
public GroupHolder(Function<T, C> grouper) {
this.grouper = grouper;
this.elements = new HashMap<>();
}
public void add(T element) {
final C key = grouper.apply(element);
elements.computeIfAbsent(key, createList)
.add(element);
}
public GroupHolder<C, T> merge(GroupHolder<C, T> holder) {
holder.elements.entrySet().forEach(e
-> elements.computeIfAbsent(e.getKey(), createList)
.addAll(e.getValue())
);
return this;
}
public MapStream<C, List<T>> finisher() {
return MapStream.of(elements);
}
}
/**
* Simple implementation class for {@code Collector}.
*
* @param <T> the type of elements to be collected
* @param <A> the type of the intermediate holder
* @param <R> the type of the result
*/
static class CollectorImpl<T, A, R> implements Collector<T, A, R> {
private final Supplier<A> supplier;
private final BiConsumer<A, T> accumulator;
private final BinaryOperator<A> combiner;
private final Function<A, R> finisher;
private final Set<Collector.Characteristics> characteristics;
CollectorImpl(Supplier<A> supplier,
BiConsumer<A, T> accumulator,
BinaryOperator<A> combiner,
Function<A, R> finisher,
Set<Collector.Characteristics> characteristics) {
this.supplier = supplier;
this.accumulator = accumulator;
this.combiner = combiner;
this.finisher = finisher;
this.characteristics = characteristics;
}
@SuppressWarnings("unchecked")
CollectorImpl(Supplier<A> supplier,
BiConsumer<A, T> accumulator,
BinaryOperator<A> combiner,
Set<Collector.Characteristics> characteristics) {
this(supplier, accumulator, combiner, i -> (R) i, characteristics);
}
@Override
public BiConsumer<A, T> accumulator() {
return accumulator;
}
@Override
public Supplier<A> supplier() {
return supplier;
}
@Override
public BinaryOperator<A> combiner() {
return combiner;
}
@Override
public Function<A, R> finisher() {
return finisher;
}
@Override
public Set<Collector.Characteristics> characteristics() {
return characteristics;
}
}
/**
* Utility classes should not be instantiated.
*/
private CollectorUtil() {
instanceNotAllowed(getClass());
}
}