code: public static String getElasticSearchBulkHeader(SimpleDataEvent event, String index, String type) {
      StringBuilder builder = new StringBuilder();
      builder.append("{\"index\":{\"_index\":\"");
      builder.append(index);
      builder.append("\",\"_type\":\"");
      builder.append(type);
      builder.append("\",\"_id\":\"");
      builder.append(event.getId());
      builder.append("\"}}");
      return builder.toString();
    }
docs: Constructs ES bulk header for the document.
  
  @param event
  data event
  @param index
  index name
  @param type
  document type
  @return ES bulk header