core/store/src/main/java/org/onlab/onos/store/impl/OptionalCacheLoader.java

package org.onlab.onos.store.impl;

import static com.google.common.base.Preconditions.checkNotNull;

import org.onlab.onos.store.common.StoreService;

import com.google.common.base.Optional;
import com.google.common.cache.CacheLoader;
import com.hazelcast.core.IMap;

/**
 * CacheLoader to wrap Map value with Optional,
 * to handle negative hit on underlying IMap.
 *
 * @param <K> IMap key type after deserialization
 * @param <V> IMap value type after deserialization
 */
public final class OptionalCacheLoader<K, V> extends
        CacheLoader<K, Optional<V>> {

    private final StoreService storeService;
    private IMap<byte[], byte[]> rawMap;

    /**
     * Constructor.
     *
     * @param storeService to use for serialization
     * @param rawMap underlying IMap
     */
    public OptionalCacheLoader(StoreService storeService, IMap<byte[], byte[]> rawMap) {
        this.storeService = checkNotNull(storeService);
        this.rawMap = checkNotNull(rawMap);
    }

    @Override
    public Optional<V> load(K key) throws Exception {
        byte[] keyBytes = storeService.serialize(key);
        byte[] valBytes = rawMap.get(keyBytes);
        if (valBytes == null) {
            return Optional.absent();
        }
        V dev = storeService.deserialize(valBytes);
        return Optional.of(dev);
    }
}