grib/src/main/java/ucar/nc2/grib/collection/Grib2Iosp.java
@Override
  public boolean isValidFile(RandomAccessFile raf) throws IOException {
    if (raf instanceof HTTPRandomAccessFile) { // only do remote if memory resident
      if (raf.length() > raf.getBufferSize())
        return false;

    } else {                                  // wont accept remote index
      GribCdmIndex.GribCollectionType type = GribCdmIndex.getType(raf);
      if (type == GribCdmIndex.GribCollectionType.GRIB2) return true;
      if (type == GribCdmIndex.GribCollectionType.Partition2) return true;
    }

    // check for GRIB2 data file
    return Grib2RecordScanner.isValidFile(raf);
  }
@Override
  public boolean isValidFile(RandomAccessFile raf) throws IOException {
    if (raf instanceof HTTPRandomAccessFile) { // only do remote if memory resident
      if (raf.length() > raf.getBufferSize())
        return false;

    } else {                                  // wont accept remote index
      GribCdmIndex.GribCollectionType type = GribCdmIndex.getType(raf);
      if (type == GribCdmIndex.GribCollectionType.GRIB2) return true;
      if (type == GribCdmIndex.GribCollectionType.Partition2) return true;
    }

    // check for GRIB2 data file
    return Grib2RecordScanner.isValidFile(raf);
  }
accept grib2 or ncx files