content: /*
   * 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.distributedlog.net;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import org.apache.bookkeeper.net.DNSToSwitchMapping;
  import org.apache.commons.lang3.StringUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  
  /**
   * Abstract DNS resolver for bookkeeper ensemble placement.
   */
  public abstract class DNSResolver implements DNSToSwitchMapping {
      static final Logger LOG = LoggerFactory.getLogger(DNSResolver.class);
  
      protected final ConcurrentMap<String, String> domainNameToNetworkLocation =
              new ConcurrentHashMap<String, String>();
  
      protected final ConcurrentMap<String, String> hostNameToRegion =
          new ConcurrentHashMap<String, String>();
  
      /**
       * Construct the default dns resolver without host-region overrides.
       */
      public DNSResolver() {
          this("");
      }
  
      /**
       * Construct the dns resolver with host-region overrides.
       *
       *  <p><i>hostRegionOverrides</i> is a string of pairs of host-region mapping
       * (host:region) separated by ';'. during dns resolution, the host will be resolved
       * to override region. example: <i>host1:region1;host2:region2;...</i>
       *
       * @param hostRegionOverrides
       *          pairs of host-region mapping separated by ';'
       */
      public DNSResolver(String hostRegionOverrides) {
          if (StringUtils.isNotBlank(hostRegionOverrides)) {
              // Host Region Overrides are of the form
              // HN1:R1;HN2:R2;...
              String[] overrides = hostRegionOverrides.split(";");
  
              for (String override : overrides) {
                  String[] parts = override.split(":");
                  if (parts.length != 2) {
                      LOG.warn("Incorrect override specified : {}", override);
                  } else {
                      hostNameToRegion.putIfAbsent(parts[0], parts[1]);
                  }
              }
          } // otherwise, no overrides were specified
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public List<String> resolve(List<String> names) {
          List<String> networkLocations = new ArrayList<String>(names.size());
          for (String name : names) {
              networkLocations.add(resolve(name));
          }
          return networkLocations;
      }
  
      private String resolve(String domainName) {
          String networkLocation = domainNameToNetworkLocation.get(domainName);
          if (null == networkLocation) {
              networkLocation = resolveToNetworkLocation(domainName);
              domainNameToNetworkLocation.put(domainName, networkLocation);
          }
          return networkLocation;
      }
  
      /**
       * Resolve the <code>domainName</code> to its network location.
       *
       * @param domainName
       *          domain name
       * @return the network location of <i>domainName</i>
       */
      protected abstract String resolveToNetworkLocation(String domainName);
  
      /**
       * {@inheritDoc}
       */
      @Override
      public void reloadCachedMappings() {
          domainNameToNetworkLocation.clear();
      }
  }
  