How to differentiate between empty string and null with OpenCSV

Question

This is my code:

CSVReader reader = new CSVReader(isReader);
while ((col = reader.readNext()) != null) {
   String c1 = col[1];
}

this is my csv file:

"a","","c"
"1",,"3"

Is there a way I can differentiate between null and ""? OpenCSV seems to treat everything as non-null String. Can I tell it to treat empty fields as null?

Cary Li · Accepted Answer · 2016-01-12 05:45:34Z

11

Adding to @Gavriel's answer, starting from OpenCSV 3.6 (maybe earlier), I found that strictQuotes doesn't help with returning null anymore.

CSVReaderBuilder has withFieldAsNull() for this purpose.

CSVReader csvReader = new CSVReaderBuilder(csvFileReader)
    .withFieldAsNull(CSVReaderNullFieldIndicator.EMPTY_SEPARATORS)
    .build();

answered Jan 12, 2016 at 5:45

Cary Li

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3 Comments

Olgun Kaya Over a year ago

I believe this must be the correct answer, since most of the reader constructors are Deprecated. By the way the indicator has BOTH option as well which considers both empty seperators and empty quotes as null.

lukass77 Over a year ago

works for me only when set "withFieldAsNull" on CSVParserBuilder , not on CSVReaderBuilder , first create CSVParserBuilder , and with it create CSVReaderBuilder like this - CSVReaderBuilder(new CSVParserBuilder(...)) - (open csv 5.0)

Krusty the Clown Over a year ago

is there a way to do it by column?

lukass77 · Accepted Answer · 2020-03-01 10:38:39Z

7

with open csv 5.0

CSVParser csvParser = new CSVParserBuilder()
                        .withSeparator(",")
                        .withQuoteChar('"')
                        .withFieldAsNull(CSVReaderNullFieldIndicator.BOTH)
                        .build();

                csvReader = new CSVReaderBuilder(new InputStreamReader(...))
                        .withCSVParser(csvParser)
                        .build();

answered Mar 1, 2020 at 10:38

lukass77

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1 Comment

Terrence Wei Over a year ago

shoud use CSVReaderNullFieldIndicator.EMPTY_SEPARATORS instead of CSVReaderNullFieldIndicator.BOTH, then the result will be a,,c and 1,null,3

Andremoniy · Accepted Answer · 2019-08-27 08:31:44Z

3

It is not possible. There is no difference between an empty string and the java specific null in the CSV format's philosophy. The null is an empty reference in the java object memory model. In CSV there aren't any references, but only empty values.

edited Aug 27, 2019 at 8:31

answered Aug 14, 2014 at 6:46

Andremoniy

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4 Comments

Gavriel Over a year ago

There is. In the above csv example I would expect opencsv to notice the difference between ,, and ,"",. I would be OK with the default being convert everything to non-null String, but I would expect to have an optional parameter where I could override the default behavior and let opencsv know that whenever it sees a certain string it should consider it as NULL. But in order for this to work it has to be inside the parser (I can't extend opencsv to add this IMHO) because in the level I get to the data it's already converted to ""

Andremoniy Over a year ago

@Gavriel, according to CSV format, ,, and ,"", are same things.

Gavriel Over a year ago

where is that standard? I thought there is no csv RFC yet

Gavriel Over a year ago

I don't see anything about empty fields there.

Gavriel · Accepted Answer · 2014-08-14 12:07:35Z

2

I found the solution: strictQuotes can be used to get nulls:

CSVReader reader = new CSVReader(isReader, ',', '"', true);
while ((col = reader.readNext()) != null) {
   String c1 = col[1];
   if (null != c1) {
       // ...
   }
}

answered Aug 14, 2014 at 12:07

Gavriel

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