Ok, but the documentation says different? The C-library is needed like you
say (and I have it installed) and used by Java-library via JNI?
https://docs.unidata.ucar.edu/netcdf-java/current/userguide/writing_netcdf.html
https://docs.unidata.ucar.edu/netcdf-java/current/userguide/netcdf4_c_library.html
And I can create new files by using
NetcdfFormatWriter.openExisting("/temp/input.nc").setFormat(NetcdfFileFormat
.NETCDF4); // note that I dont call "setNewFile(false)"
(This will create a file called "input.nc" but much smaller and containing
variables filled with "garbage" data.. but the file is still written and
readable)
Den ons 7 apr. 2021 kl 19:50 skrev John Caron <jcaron1129@xxxxxxxxx>:
> Hi Andreas:
>
> Netcdf-Java does not support writing or modifying netcdf-4 files. You need
> to use the netcdf-4 C library directly. Sorry.
>
> John
>
> On Wed, Apr 7, 2021 at 8:49 AM Andreas Imner <andreas.imner@xxxxxxxxx>
> wrote:
>
>> (... 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());
>>>
>>>
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