jstorm-core/src/main/java/storm/trident/state/CombinerValueUpdater.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 storm.trident.state;

import storm.trident.operation.CombinerAggregator;

public class CombinerValueUpdater implements ValueUpdater<Object> {
    Object arg;
    CombinerAggregator agg;

    public CombinerValueUpdater(CombinerAggregator agg, Object arg) {
        this.agg = agg;
        this.arg = arg;
    }

    @Override
    public Object update(Object stored) {
        if (stored == null)
            return arg;
        else
            return agg.combine(stored, arg);
    }
}