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

• To: netcdf-java@xxxxxxxxxxxxxxxx
• Subject: [netcdf-java] How to modify variable in existing netcdf4 file?
• From: Andreas Imner <andreas.imner@xxxxxxxxx>
• Date: Wed, 7 Apr 2021 16:33:18 +0200

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());

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