grib/src/main/java/ucar/nc2/grib/collection/GribCollectionMutable.java
private String getIndexFilepathInCache() {
    File indexFile = GribCdmIndex.makeIndexFile(name, directory);
    return GribIndexCache.getFileOrCache(indexFile.getPath()).getPath();
  }
private String getIndexFilepathInCache() {
    File indexFile = GribCdmIndex.makeIndexFile(name, directory);
    return GribIndexCache.getFileOrCache(indexFile.getPath()).getPath();
  }
get index filename

@return index filename; may not exist; may be in disk cache