001/**
002 *
003 * Licensed to the Apache Software Foundation (ASF) under one
004 * or more contributor license agreements.  See the NOTICE file
005 * distributed with this work for additional information
006 * regarding copyright ownership.  The ASF licenses this file
007 * to you under the Apache License, Version 2.0 (the
008 * "License"); you may not use this file except in compliance
009 * with the License.  You may obtain a copy of the License at
010 *
011 * http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing, software
014 * distributed under the License is distributed on an "AS IS" BASIS,
015 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
016 * See the License for the specific language governing permissions and
017 * limitations under the License.
018 */
019
020package org.apache.hadoop.hbase.metrics;
021
022import java.util.ArrayList;
023import java.util.List;
024import java.util.ServiceLoader;
025
026import org.apache.hadoop.hbase.util.ReflectionUtils;
027import org.apache.yetus.audience.InterfaceAudience;
028import org.slf4j.Logger;
029import org.slf4j.LoggerFactory;
030
031import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting;
032
033@InterfaceAudience.Private
034public final class MetricRegistriesLoader {
035  private static final Logger LOG = LoggerFactory.getLogger(MetricRegistries.class);
036
037  private static final String defaultClass
038      = "org.apache.hadoop.hbase.metrics.impl.MetricRegistriesImpl";
039
040  private MetricRegistriesLoader() {
041  }
042
043  /**
044   * Creates a {@link MetricRegistries} instance using the corresponding {@link MetricRegistries}
045   * available to {@link ServiceLoader} on the classpath. If no instance is found, then default
046   * implementation will be loaded.
047   * @return A {@link MetricRegistries} implementation.
048   */
049  public static MetricRegistries load() {
050    List<MetricRegistries> availableImplementations = getDefinedImplemantations();
051    return load(availableImplementations);
052  }
053
054  /**
055   * Creates a {@link MetricRegistries} instance using the corresponding {@link MetricRegistries}
056   * available to {@link ServiceLoader} on the classpath. If no instance is found, then default
057   * implementation will be loaded.
058   * @return A {@link MetricRegistries} implementation.
059   */
060  @VisibleForTesting
061  static MetricRegistries load(List<MetricRegistries> availableImplementations) {
062
063    if (availableImplementations.size() == 1) {
064      // One and only one instance -- what we want/expect
065      MetricRegistries impl = availableImplementations.get(0);
066      LOG.info("Loaded MetricRegistries " + impl.getClass());
067      return impl;
068    } else if (availableImplementations.isEmpty()) {
069      try {
070        return ReflectionUtils.newInstance((Class<MetricRegistries>)Class.forName(defaultClass));
071      } catch (ClassNotFoundException e) {
072        throw new RuntimeException(e);
073      }
074    } else {
075      // Tell the user they're doing something wrong, and choose the first impl.
076      StringBuilder sb = new StringBuilder();
077      for (MetricRegistries factory : availableImplementations) {
078        if (sb.length() > 0) {
079          sb.append(", ");
080        }
081        sb.append(factory.getClass());
082      }
083      LOG.warn("Found multiple MetricRegistries implementations: " + sb
084          + ". Using first found implementation: " + availableImplementations.get(0));
085      return availableImplementations.get(0);
086    }
087  }
088
089  private static List<MetricRegistries> getDefinedImplemantations() {
090    ServiceLoader<MetricRegistries> loader = ServiceLoader.load(MetricRegistries.class);
091    List<MetricRegistries> availableFactories = new ArrayList<>();
092    for (MetricRegistries impl : loader) {
093      availableFactories.add(impl);
094    }
095    return availableFactories;
096  }
097}