Count.java example

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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.flink.graph.asm.dataset;

import org.apache.flink.api.common.accumulators.LongCounter;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.graph.AnalyticHelper;

import java.io.IOException;

/**
 * Count the number of elements in a {@link DataSet}.
 *
 * @param <T> element type
 */
public class Count<T>
extends AbstractDataSetAnalytic<T, Long> {

	private static final String COUNT = "count";

	private CountHelper<T> countHelper;

	@Override
	public Count<T> run(DataSet<T> input)
			throws Exception {
		super.run(input);

		countHelper = new CountHelper<>();

		input
			.output(countHelper)
				.name("Count");

		return this;
	}

	@Override
	public Long getResult() {
		return countHelper.getAccumulator(env, COUNT);
	}

	/**
	 * Helper class to count elements.
	 *
	 * @param <U> element type
	 */
	private static class CountHelper<U>
	extends AnalyticHelper<U> {
		private long count;

		@Override
		public void writeRecord(U record) throws IOException {
			count++;
		}

		@Override
		public void close() throws IOException {
			addAccumulator(COUNT, new LongCounter(count));
		}
	}
}