public IndexMetaData build() {
      MapBuilder<String, AliasMetaData> tmpAliases = aliases;
      Settings tmpSettings = settings;

      // For backward compatibility
      String[] legacyAliases = settings.getAsArray("index.aliases");
      if (legacyAliases.length > 0) {
        tmpAliases = MapBuilder.newMapBuilder();
        for (String alias : legacyAliases) {
          AliasMetaData aliasMd = AliasMetaData.newAliasMetaDataBuilder(alias).build();
          tmpAliases.put(alias, aliasMd);
        }
        tmpAliases.putAll(aliases.immutableMap());
        // Remove index.aliases from settings once they are migrated to the new data structure
        tmpSettings =
            ImmutableSettings.settingsBuilder().put(settings).putArray("index.aliases").build();
      }

      // update default mapping on the MappingMetaData
      if (mappings.containsKey(MapperService.DEFAULT_MAPPING)) {
        MappingMetaData defaultMapping = mappings.get(MapperService.DEFAULT_MAPPING);
        for (MappingMetaData mappingMetaData : mappings.map().values()) {
          mappingMetaData.updateDefaultMapping(defaultMapping);
        }
      }

      return new IndexMetaData(
          index,
          version,
          state,
          tmpSettings,
          mappings.immutableMap(),
          tmpAliases.immutableMap(),
          customs.immutableMap());
    }
 public Builder putAlias(AliasMetaData aliasMetaData) {
   aliases.put(aliasMetaData.alias(), aliasMetaData);
   return this;
 }