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
031@InterfaceAudience.Private
032public final class MetricRegistriesLoader {
033  private static final Logger LOG = LoggerFactory.getLogger(MetricRegistries.class);
034
035  private static final String defaultClass
036      = "org.apache.hadoop.hbase.metrics.impl.MetricRegistriesImpl";
037
038  private MetricRegistriesLoader() {
039  }
040
041  /**
042   * Creates a {@link MetricRegistries} instance using the corresponding {@link MetricRegistries}
043   * available to {@link ServiceLoader} on the classpath. If no instance is found, then default
044   * implementation will be loaded.
045   * @return A {@link MetricRegistries} implementation.
046   */
047  public static MetricRegistries load() {
048    List<MetricRegistries> availableImplementations = getDefinedImplemantations();
049    return load(availableImplementations);
050  }
051
052  /**
053   * Creates a {@link MetricRegistries} instance using the corresponding {@link MetricRegistries}
054   * available to {@link ServiceLoader} on the classpath. If no instance is found, then default
055   * implementation will be loaded.
056   * @return A {@link MetricRegistries} implementation.
057   */
058  static MetricRegistries load(List<MetricRegistries> availableImplementations) {
059
060    if (availableImplementations.size() == 1) {
061      // One and only one instance -- what we want/expect
062      MetricRegistries impl = availableImplementations.get(0);
063      LOG.info("Loaded MetricRegistries " + impl.getClass());
064      return impl;
065    } else if (availableImplementations.isEmpty()) {
066      try {
067        return ReflectionUtils.newInstance((Class<MetricRegistries>)Class.forName(defaultClass));
068      } catch (ClassNotFoundException e) {
069        throw new RuntimeException(e);
070      }
071    } else {
072      // Tell the user they're doing something wrong, and choose the first impl.
073      StringBuilder sb = new StringBuilder();
074      for (MetricRegistries factory : availableImplementations) {
075        if (sb.length() > 0) {
076          sb.append(", ");
077        }
078        sb.append(factory.getClass());
079      }
080      LOG.warn("Found multiple MetricRegistries implementations: " + sb
081          + ". Using first found implementation: " + availableImplementations.get(0));
082      return availableImplementations.get(0);
083    }
084  }
085
086  private static List<MetricRegistries> getDefinedImplemantations() {
087    ServiceLoader<MetricRegistries> loader = ServiceLoader.load(MetricRegistries.class);
088    List<MetricRegistries> availableFactories = new ArrayList<>();
089    for (MetricRegistries impl : loader) {
090      availableFactories.add(impl);
091    }
092    return availableFactories;
093  }
094}