code: public void setExportOnlyColumns(final String[] exportOnlyColumns) {
          if (exportOnlyColumns != null) {
              this.exportOnlyColumns = exportOnlyColumns.clone();
          } else {
              this.exportOnlyColumns = null;
          }
      }
docs: When set, only columns contained in the String[] will
  be exported out to Excel.
  
  @param exportOnlyColumns the exportOnlyColumns to set