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