hadoop EmptyIOStatistics 源码
haddop EmptyIOStatistics 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/statistics/impl/EmptyIOStatistics.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.hadoop.fs.statistics.impl;
import java.util.Map;
import org.apache.hadoop.fs.statistics.IOStatistics;
import org.apache.hadoop.fs.statistics.MeanStatistic;
import static java.util.Collections.emptyMap;
/**
* An empty IO Statistics implementation for classes which always
* want to return a non-null set of statistics.
*/
final class EmptyIOStatistics extends AbstractIOStatisticsImpl {
/**
* The sole instance of this class.
*/
private static final EmptyIOStatistics INSTANCE = new EmptyIOStatistics();
private EmptyIOStatistics() {
}
@Override
public Map<String, Long> counters() {
return emptyMap();
}
@Override
public Map<String, Long> gauges() {
return emptyMap();
}
@Override
public Map<String, Long> minimums() {
return emptyMap();
}
@Override
public Map<String, Long> maximums() {
return emptyMap();
}
@Override
public Map<String, MeanStatistic> meanStatistics() {
return emptyMap();
}
/**
* Get the single instance of this class.
* @return a shared, empty instance.
*/
public static IOStatistics getInstance() {
return INSTANCE;
}
}
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