com.github.richardballard.arbeeutils.stream.MoreCollectors Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of arbee-utils Show documentation
A collection of utilities that I find useful across various projects
There is a newer version: 2.0
/*
 * (C) Copyright 2016 Richard Ballard.
 *
 * 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.github.richardballard.arbeeutils.stream;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import net.jcip.annotations.Immutable;
import org.jetbrains.annotations.NotNull;

import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

/**
 * Some extra {@link Collector} implementations for things like guava lists.
 */
@Immutable
public enum MoreCollectors {
    ;

    /**
     * Based on code from here
     */
    @NotNull
    public static  Collector> toImmutableList() {

        final Supplier> supplier = ImmutableList.Builder::new;

        final BiConsumer, T> accumulator = ImmutableList.Builder::add;

        final BinaryOperator> combiner = (l, r) -> l.addAll(r.build());

        final Function, ImmutableList> finisher = ImmutableList.Builder::build;

        return Collector.of(supplier,
                            accumulator,
                            combiner,
                            finisher);
    }

    /**
     * Based on code from here
     */
    @NotNull
    public static  Collector> toImmutableSet() {

        final Supplier> supplier = ImmutableSet.Builder::new;

        final BiConsumer, T> accumulator = ImmutableSet.Builder::add;

        final BinaryOperator> combiner = (l, r) -> l.addAll(r.build());

        final Function, ImmutableSet> finisher = ImmutableSet.Builder::build;

        return Collector.of(supplier,
                            accumulator,
                            combiner,
                            finisher);
    }

    /**
     * Based on code from here
     */
    @NotNull
    public static  Collector>
    toImmutableMap(@NotNull final Function keyMapper,
                   @NotNull final Function valueMapper) {
        assert keyMapper != null;
        assert valueMapper != null;

        final Supplier> supplier = ImmutableMap.Builder::new;

        final BiConsumer, T> accumulator = (b, t) -> b.put(keyMapper.apply(t),
                                                                                      valueMapper.apply(t));

        final BinaryOperator> combiner = (l, r) -> l.putAll(r.build());

        final Function, ImmutableMap> finisher = ImmutableMap.Builder::build;

        return Collector.of(supplier,
                            accumulator,
                            combiner,
                            finisher);
    }
}