com.github.jeluard.guayaba.util.concurrent.ConcurrentMaps.java Source code

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/**
 * Copyright 2012 Julien Eluard
 * This project includes software developed by Julien Eluard: https://github.com/jeluard/
 *
 * 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.jeluard.guayaba.util.concurrent;

import com.google.common.base.Preconditions;
import com.google.common.base.Supplier;

import java.util.concurrent.ConcurrentMap;

/**
 * Helper methods for {@link ConcurrentMap}s.
 */
public final class ConcurrentMaps {

    private ConcurrentMaps() {
    }

    /**
     * Returns value associated with key if exists.
     * Otherwise create value using provided {@link Supplier}, insert it map then returns it.
     *
     * TODO improve based on http://blog.boundary.com/2011/05/
     *
     * @param <K>
     * @param <V>
     * @param concurrentMap
     * @param key
     * @param supplier
     * @return previous value if exists; result of {@link Supplier#get()} otherwise
     */
    public static synchronized <K, V> V putIfAbsentAndReturn(final ConcurrentMap<K, V> concurrentMap, final K key,
            final Supplier<V> supplier) {
        Preconditions.checkNotNull(concurrentMap, "null concurrentMap");
        Preconditions.checkNotNull(key, "null key");
        Preconditions.checkNotNull(supplier, "null supplier");

        if (concurrentMap.containsKey(key)) {
            return concurrentMap.get(key);
        }

        final V value = supplier.get();
        concurrentMap.put(key, value);
        return value;
    }

}