grib/src/main/java/ucar/nc2/grib/GribIndexCache.java
public static File getExistingFileOrCache(String fileLocation) {
    File result =  getDiskCache2().getExistingFileOrCache(fileLocation);
    if (result == null && Grib.debugGbxIndexOnly && fileLocation.endsWith(".gbx9.ncx4")) { // might create only from gbx9 for debugging
      int length = fileLocation.length();
      String maybeIndexAlreadyExists = fileLocation.substring(0, length-10)+".ncx4";
      result =  getDiskCache2().getExistingFileOrCache(maybeIndexAlreadyExists);
    }
    return result;
  }
public static File getExistingFileOrCache(String fileLocation) {
    File result =  getDiskCache2().getExistingFileOrCache(fileLocation);
    if (result == null && Grib.debugGbxIndexOnly && fileLocation.endsWith(".gbx9.ncx4")) { // might create only from gbx9 for debugging
      int length = fileLocation.length();
      String maybeIndexAlreadyExists = fileLocation.substring(0, length-10)+".ncx4";
      result =  getDiskCache2().getExistingFileOrCache(maybeIndexAlreadyExists);
    }
    return result;
  }
Looking for an existing file, in cache or not

@param fileLocation full path of original index filename
@return existing file if you can find it, else null