com.fatboyindustrial.omnium.ImmutableCollectors.java Source code

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Here is the source code for com.fatboyindustrial.omnium.ImmutableCollectors.java

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/*
 * Copyright 2015 Greg Kopff
 * All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package com.fatboyindustrial.omnium;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ImmutableSortedMap;
import com.google.common.collect.ImmutableSortedSet;

import javax.annotation.concurrent.Immutable;
import java.util.function.Function;
import java.util.stream.Collector;

import static java.util.stream.Collector.Characteristics.UNORDERED;

/**
 * A set of collectors that return Guava immutable collections.
 */
@Immutable
public class ImmutableCollectors {
    /**
     * Gets a collector that returns an {@link ImmutableList}.
     * @param <T> The type of element in the list.
     * @return The collector.
     */
    public static <T> Collector<T, ImmutableList.Builder<T>, ImmutableList<T>> toImmutableList() {
        return Collector.of(ImmutableList::builder, (list, entry) -> list.add(entry),
                (builder1, builder2) -> builder1.addAll(builder2.build()), ImmutableList.Builder::build);
    }

    /**
     * Gets a collector that returns an {@link ImmutableSet}.
     * @param <T> The type of element in the set.
     * @return The collector.
     */
    public static <T> Collector<T, ImmutableSet.Builder<T>, ImmutableSet<T>> toImmutableSet() {
        return Collector.of(ImmutableSet::builder, (set, entry) -> set.add(entry),
                (builder1, builder2) -> builder1.addAll(builder2.build()), ImmutableSet.Builder::build, UNORDERED);
    }

    /**
     * Gets a collector that returns an {@link ImmutableSortedSet}.
     * @param <T> The type of element in the set.
     * @return The collector.
     */
    public static <T extends Comparable<T>> Collector<T, ImmutableSortedSet.Builder<T>, ImmutableSortedSet<T>> toImmutableSortedSet() {
        return Collector.of(ImmutableSortedSet::naturalOrder, (set, entry) -> set.add(entry),
                (builder1, builder2) -> builder1.addAll(builder2.build()), ImmutableSortedSet.Builder::build,
                UNORDERED);
    }

    /**
     * Gets a collector that returns an {@link ImmutableMap}.
     * @param <T> The original element type.
     * @param <K> The key type.
     * @param <V> The value type.
     * @param keyMapper Function to transform {@code T} to {@code K}.
     * @param valueMapper Function to transform {@code T} to {@code V}.
     * @return The collector.
     */
    public static <T, K, V> Collector<T, ImmutableMap.Builder<K, V>, ImmutableMap<K, V>> toImmutableMap(
            final Function<? super T, ? extends K> keyMapper, final Function<? super T, ? extends V> valueMapper) {
        return Collector.of(ImmutableMap::builder,
                (map, entry) -> map.put(keyMapper.apply(entry), valueMapper.apply(entry)),
                (builder1, builder2) -> builder1.putAll(builder2.build()), ImmutableMap.Builder::build, UNORDERED);
    }

    /**
     * Gets a collector that returns an {@link ImmutableMap}, with the stream element used as the key,
     * and the value computed using the supplied value mapper.
     * @param <T> The original element type.
     * @param <V> The value type.
     * @param valueMapper Function to transform {@code T} to {@code V}.
     * @return The collector.
     */
    public static <T, V> Collector<T, ImmutableMap.Builder<T, V>, ImmutableMap<T, V>> asKeyToImmutableMap(
            final Function<? super T, ? extends V> valueMapper) {
        return toImmutableMap(Function.identity(), valueMapper);
    }

    /**
     * Gets a collector that returns an {@link ImmutableMap}, with the stream element used as the value,
     * and the key computed using the supplied key mapper.
     * @param <T> The original element type.
     * @param <K> The key type.
     * @param keyMapper Function to transform {@code T} to {@code K}.
     * @return The collector.
     */
    public static <T, K> Collector<T, ImmutableMap.Builder<K, T>, ImmutableMap<K, T>> asValueToImmutableMap(
            final Function<? super T, ? extends K> keyMapper) {
        return toImmutableMap(keyMapper, Function.identity());
    }

    /**
     * Gets a collector that returns an {@link ImmutableSortedMap}.
     * @param <T> The original element type.
     * @param <K> The key type.
     * @param <V> The value type.
     * @param keyMapper Function to transform {@code T} to {@code K}.
     * @param valueMapper Function to transform {@code T} to {@code V}.
     * @return The collector.
     */
    public static <T, K extends Comparable<K>, V> Collector<T, ImmutableSortedMap.Builder<K, V>, ImmutableSortedMap<K, V>> toImmutableSortedMap(
            final Function<? super T, ? extends K> keyMapper, final Function<? super T, ? extends V> valueMapper) {
        return Collector.of(ImmutableSortedMap::naturalOrder,
                (map, entry) -> map.put(keyMapper.apply(entry), valueMapper.apply(entry)),
                (builder1, builder2) -> builder1.putAll(builder2.build()), ImmutableSortedMap.Builder::build,
                UNORDERED);
    }
}