private FieldSelector buildFieldSelectors(DocumentMapper docMapper, String... fields) {
    if (fields == null) {
      return docMapper.sourceMapper().fieldSelector();
    }

    // don't load anything
    if (fields.length == 0) {
      return null;
    }

    FieldMappersFieldSelector fieldSelector = null;
    for (String fieldName : fields) {
      FieldMappers x = docMapper.mappers().smartName(fieldName);
      if (x != null && x.mapper().stored()) {
        if (fieldSelector == null) {
          fieldSelector = new FieldMappersFieldSelector();
        }
        fieldSelector.add(x);
      }
    }

    return fieldSelector;
  }
  @Override
  protected GetResponse shardOperation(GetRequest request, int shardId)
      throws ElasticSearchException {
    IndexService indexService = indicesService.indexServiceSafe(request.index());
    BloomCache bloomCache = indexService.cache().bloomCache();
    IndexShard indexShard = indexService.shardSafe(shardId);

    DocumentMapper docMapper = indexService.mapperService().documentMapper(request.type());
    if (docMapper == null) {
      throw new TypeMissingException(new Index(request.index()), request.type());
    }

    if (request.refresh()) {
      indexShard.refresh(new Engine.Refresh(false));
    }

    Engine.Searcher searcher = indexShard.searcher();
    boolean exists = false;
    byte[] source = null;
    Map<String, GetField> fields = null;
    long version = -1;
    try {
      UidField.DocIdAndVersion docIdAndVersion =
          loadCurrentVersionFromIndex(
              bloomCache, searcher, docMapper.uidMapper().term(request.type(), request.id()));
      if (docIdAndVersion != null && docIdAndVersion.docId != Lucene.NO_DOC) {
        if (docIdAndVersion.version > 0) {
          version = docIdAndVersion.version;
        }
        exists = true;
        FieldSelector fieldSelector = buildFieldSelectors(docMapper, request.fields());
        if (fieldSelector != null) {
          Document doc = docIdAndVersion.reader.document(docIdAndVersion.docId, fieldSelector);
          source = extractSource(doc, docMapper);

          for (Object oField : doc.getFields()) {
            Fieldable field = (Fieldable) oField;
            String name = field.name();
            Object value = null;
            FieldMappers fieldMappers = docMapper.mappers().indexName(field.name());
            if (fieldMappers != null) {
              FieldMapper mapper = fieldMappers.mapper();
              if (mapper != null) {
                name = mapper.names().fullName();
                value = mapper.valueForSearch(field);
              }
            }
            if (value == null) {
              if (field.isBinary()) {
                value = field.getBinaryValue();
              } else {
                value = field.stringValue();
              }
            }

            if (fields == null) {
              fields = newHashMapWithExpectedSize(2);
            }

            GetField getField = fields.get(name);
            if (getField == null) {
              getField = new GetField(name, new ArrayList<Object>(2));
              fields.put(name, getField);
            }
            getField.values().add(value);
          }
        }

        // now, go and do the script thingy if needed
        if (request.fields() != null && request.fields().length > 0) {
          SearchLookup searchLookup = null;
          for (String field : request.fields()) {
            String script = null;
            if (field.contains("_source.") || field.contains("doc[")) {
              script = field;
            } else {
              FieldMappers x = docMapper.mappers().smartName(field);
              if (x != null && !x.mapper().stored()) {
                script = "_source." + x.mapper().names().fullName();
              }
            }
            if (script != null) {
              if (searchLookup == null) {
                searchLookup =
                    new SearchLookup(
                        indexService.mapperService(), indexService.cache().fieldData());
              }
              SearchScript searchScript = scriptService.search(searchLookup, "mvel", script, null);
              searchScript.setNextReader(docIdAndVersion.reader);
              searchScript.setNextDocId(docIdAndVersion.docId);

              try {
                Object value = searchScript.run();
                if (fields == null) {
                  fields = newHashMapWithExpectedSize(2);
                }
                GetField getField = fields.get(field);
                if (getField == null) {
                  getField = new GetField(field, new ArrayList<Object>(2));
                  fields.put(field, getField);
                }
                getField.values().add(value);
              } catch (RuntimeException e) {
                if (logger.isTraceEnabled()) {
                  logger.trace("failed to execute get request script field [{}]", e, script);
                }
                // ignore
              }
            }
          }
        }
      }
    } catch (IOException e) {
      throw new ElasticSearchException(
          "Failed to get type [" + request.type() + "] and id [" + request.id() + "]", e);
    } finally {
      searcher.release();
    }
    return new GetResponse(
        request.index(), request.type(), request.id(), version, exists, source, fields);
  }