Re: [netcdf-java] How to modify variable in existing netcdf4 file?

• To: netcdf-java@xxxxxxxxxxxxxxxx
• Subject: Re: [netcdf-java] How to modify variable in existing netcdf4 file?
• From: Andreas Imner <andreas.imner@xxxxxxxxx>
• Date: Wed, 7 Apr 2021 16:49:05 +0200

(... continuing since I clicked "Send" to soon)

The NPE occurs because the 'ncfile.getLocation()' returns null

My question is, is this supposed to work and am I doing something wrong?
Or maybe this is not the way you are supposed to work with NetCDF -files
that you want to modify the contents of?

Den ons 7 apr. 2021 kl 16:33 skrev Andreas Imner <andreas.imner@xxxxxxxxx>:

> Hi!
> A am trying to use the Java NetCDF library to modify the data of a
> variable in an existing NetCDF4 file.
>
> I use the 5.4.1 version of the Java library
> I have version 4.7.4_2 of the netcdf C-library installed and it works
> properly.
>
> The problem I get is that when opening the existing file for writing, a
> NPE is thrown.
>
> My code looks something like this...
>
> NetcdfFormatWriter.Builder builder = 
> NetcdfFormatWriter.openExisting("/temp/input.nc").setFormat(NetcdfFileFormat.NETCDF4).setNewFile(false);
> NetcdfFormatWriter writer = builder.build();
>
> But when .build() is called an exception is thrown
>
> Exception in thread "main" java.lang.NullPointerException
>       at ucar.nc2.NetcdfFiles.canonicalizeUriString(NetcdfFiles.java:359)
>       at ucar.nc2.jni.netcdf.Nc4Iosp._open(Nc4Iosp.java:253)
>       at ucar.nc2.jni.netcdf.Nc4Iosp.openForWriting(Nc4Iosp.java:239)
>       at ucar.nc2.write.NetcdfFormatWriter.<init>(NetcdfFormatWriter.java:329)
>       at ucar.nc2.write.NetcdfFormatWriter.<init>(NetcdfFormatWriter.java:49)
>       at 
> ucar.nc2.write.NetcdfFormatWriter$Builder.build(NetcdfFormatWriter.java:261)
>
> Looking at the code in the class Nc4Iosp.java
>
> private void _open(RandomAccessFile raf, NetcdfFile ncfile, boolean readOnly) 
> throws IOException {
>     ...
> String location = NetcdfFiles.canonicalizeUriString(ncfile.getLocation());
>
>
>

• Follow-Ups:
  • Re: [netcdf-java] How to modify variable in existing netcdf4 file?
    • From: John Caron

• References:
  • [netcdf-java] How to modify variable in existing netcdf4 file?
    • From: Andreas Imner