A Panoply user has been having trouble opening a GRIB dataset due to an exception thrown from somewhere inside the NJ library. The exception is caught and re-thrown by NetcdfFile.open(), but further tracing reveals something going on when Gri1IOSP tries to open the file.
java.io.IOException: java.lang.IllegalArgumentException: Attribute value cannot be null at ucar.nc2.NetcdfFile.open(NetcdfFile.java:425) at ucar.nc2.dataset.NetcdfDataset.openOrAcquireFile(NetcdfDataset.java:699) at ucar.nc2.dataset.NetcdfDataset.openDataset(NetcdfDataset.java:421) at ucar.nc2.dataset.NetcdfDataset.acquireDataset(NetcdfDataset.java:516) at ucar.nc2.dataset.NetcdfDataset.acquireDataset(NetcdfDataset.java:493) at gov.nasa.giss.netcdf.NcDataset.init(NcDataset.java:118) ... more Caused by: java.lang.IllegalArgumentException: Attribute value cannot be null at ucar.nc2.Attribute.setStringValue(Attribute.java:508) at ucar.nc2.Attribute.<init>(Attribute.java:370) at ucar.nc2.grib.grib1.Grib1Iosp.addGroup(Grib1Iosp.java:338) at ucar.nc2.grib.grib1.Grib1Iosp.open(Grib1Iosp.java:160) at ucar.nc2.NetcdfFile.<init>(NetcdfFile.java:1521) at ucar.nc2.NetcdfFile.open(NetcdfFile.java:813) at ucar.nc2.NetcdfFile.open(NetcdfFile.java:422) ... 16 more
I'm at a loss as to what to tell the user, as there's no further info presented about what attribute it is that has a null value. It would be of some help if the exception would also report the name/key of the problem attribute.
A copy of the dataset is currently at http://www.giss.nasa.gov/staff/rschmunk/data/20130917_153410_.grb
Ill add a better error message when i get back.
BTW: I commented last March that I had been having since the start of the year with GRIB temporary files popping up in the same directory as the GRIB file rather than in the cache dir specified by DiskCache.setRootDirectory(). I thought this was "fixed" in 4.3.18 but that was mistaken. On further exploration today, I found that a deliberate change was made in 4.3.15, as described at http://www.unidata.ucar.edu/software/thredds/current/netcdf-java/reference/Caching.html
However, although that webpage states that as of 4.3.15 one should use DiskCache2 class to deal with GRIB files, the section terminates before providing an example of the DiskCache2 options. I did find an example in the source code for the TestGribDiskCache class which gave me the help I needed.
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