org.apache.james.util.streams.ImmutableCollectors.java Source code

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 * regarding copyright ownership.  The ASF licenses this file   *
 * to you under the Apache License, Version 2.0 (the            *
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package org.apache.james.util.streams;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collector;

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

public class ImmutableCollectors {

    public static <T> Collector<T, List<T>, ImmutableList<T>> toImmutableList() {
        return Collector.of(ArrayList::new, List::add, (left, right) -> {
            left.addAll(right);
            return left;
        }, ImmutableList::copyOf);
    }

    public static <T> Collector<T, ImmutableSet.Builder<T>, ImmutableSet<T>> toImmutableSet() {
        return Collector.of(ImmutableSet::builder, ImmutableSet.Builder::add, (left, right) -> {
            left.addAll(right.build());
            return left;
        }, ImmutableSet.Builder::build);
    }

    public static <T, K, V> Collector<T, ImmutableMap.Builder<K, V>, ImmutableMap<K, V>> toImmutableMap(
            Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends V> valueMapper) {
        return Collector.of(ImmutableMap::<K, V>builder,
                (acc, v) -> acc.put(keyMapper.apply(v), valueMapper.apply(v)),
                (map1, map2) -> map1.putAll(map2.build()), ImmutableMap.Builder::build);
    }
}