storm-client/src/jvm/org/apache/storm/trident/state/map/CachedMap.java

/**
 * 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.storm.trident.state.map;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.storm.trident.util.LRUMap;

/**
 * Useful to layer over a map that communicates with a database. you generally layer opaque map over this over your database store.
 */
public class CachedMap<T> implements IBackingMap<T> {
    LRUMap<List<Object>, T> cache;
    IBackingMap<T> delegate;

    public CachedMap(IBackingMap<T> delegate, int cacheSize) {
        cache = new LRUMap<List<Object>, T>(cacheSize);
        this.delegate = delegate;
    }

    @Override
    public List<T> multiGet(List<List<Object>> keys) {
        Map<List<Object>, T> results = new HashMap<List<Object>, T>();
        List<List<Object>> toGet = new ArrayList<List<Object>>();
        for (List<Object> key : keys) {
            if (cache.containsKey(key)) {
                results.put(key, cache.get(key));
            } else {
                toGet.add(key);
            }
        }

        List<T> fetchedVals = delegate.multiGet(toGet);
        for (int i = 0; i < toGet.size(); i++) {
            List<Object> key = toGet.get(i);
            T val = fetchedVals.get(i);
            cache.put(key, val);
            results.put(key, val);
        }

        List<T> ret = new ArrayList<T>(keys.size());
        for (List<Object> key : keys) {
            ret.add(results.get(key));
        }
        return ret;
    }

    @Override
    public void multiPut(List<List<Object>> keys, List<T> values) {
        cache(keys, values);
        delegate.multiPut(keys, values);
    }

    private void cache(List<List<Object>> keys, List<T> values) {
        for (int i = 0; i < keys.size(); i++) {
            cache.put(keys.get(i), values.get(i));
        }
    }

}