org.apache.druid.server.lookup.cache.polling.OnHeapPollingCache.java Source code

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Here is the source code for org.apache.druid.server.lookup.cache.polling.OnHeapPollingCache.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.druid.server.lookup.cache.polling;

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

import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;

public class OnHeapPollingCache<K, V> implements PollingCache<K, V> {
    private final ImmutableMap<K, V> immutableMap;
    private final ImmutableMap<V, List<K>> immutableReverseMap;

    public OnHeapPollingCache(Iterable<Map.Entry<K, V>> entries) {

        if (entries == null) {
            immutableMap = ImmutableMap.of();
            immutableReverseMap = ImmutableMap.of();
        } else {
            ImmutableSet.Builder<V> setOfValuesBuilder = ImmutableSet.builder();
            ImmutableMap.Builder<K, V> mapBuilder = ImmutableMap.builder();
            for (Map.Entry<K, V> entry : entries) {
                setOfValuesBuilder.add(entry.getValue());
                mapBuilder.put(entry.getKey(), entry.getValue());
            }
            final Set<V> setOfValues = setOfValuesBuilder.build();
            immutableMap = mapBuilder.build();
            immutableReverseMap = ImmutableMap
                    .copyOf(Maps.asMap(setOfValues, val -> immutableMap.keySet().stream().filter(key -> {
                        V retVal = immutableMap.get(key);
                        return retVal != null && retVal.equals(val);
                    }).collect(Collectors.toList())));
        }

    }

    @Override
    public V get(K key) {
        return immutableMap.get(key);
    }

    @Override
    public List<K> getKeys(final V value) {
        final List<K> listOfKeys = immutableReverseMap.get(value);
        if (listOfKeys == null) {
            return Collections.emptyList();
        }
        return listOfKeys;
    }

    @Override
    public void close() {
        //noop
    }

    public static class OnHeapPollingCacheProvider<K, V> implements PollingCacheFactory<K, V> {
        @Override
        public PollingCache makeOf(Iterable<Map.Entry<K, V>> entries) {
            return new OnHeapPollingCache(entries);
        }
    }
}