grib/src/main/java/ucar/nc2/grib/GribIndexCache.java
public static File getFileOrCache(String fileLocation) {
    File result = getExistingFileOrCache(fileLocation);
    if (result != null) return result;
    return getDiskCache2().getFile(fileLocation);
  }
public static File getFileOrCache(String fileLocation) {
    File result = getExistingFileOrCache(fileLocation);
    if (result != null) return result;
    return getDiskCache2().getFile(fileLocation);
  }
Get index file, may be in cache directory, may not exist

@param fileLocation full path of original index filename
@return File, possibly in cache, may or may not exist