Good and effective CSV/TSV Reader for Java

Question

I am trying to read big CSV and TSV (tab-separated) Files with about 1000000 rows or more. Now I tried to read a TSV containing ~2500000 lines with opencsv, but it throws me an java.lang.NullPointerException. It works with smaller TSV Files with ~250000 lines. So I was wondering if there are any other Libraries that support the reading of huge CSV and TSV Files. Do you have any ideas?

Everybody who is interested in my Code (I shorten it, so Try-Catch is obviously invalid):

InputStreamReader in = null;
CSVReader reader = null;
try {
    in = this.replaceBackSlashes();
    reader = new CSVReader(in, this.seperator, '\"', this.offset);
    ret = reader.readAll();
} finally {
    try {
        reader.close();
    } 
}

Edit: This is the Method where I construct the InputStreamReader:

private InputStreamReader replaceBackSlashes() throws Exception {
        FileInputStream fis = null;
        Scanner in = null;
        try {
            fis = new FileInputStream(this.csvFile);
            in = new Scanner(fis, this.encoding);
            ByteArrayOutputStream out = new ByteArrayOutputStream();

            while (in.hasNext()) {
                String nextLine = in.nextLine().replace("\\", "/");
                // nextLine = nextLine.replaceAll(" ", "");
                nextLine = nextLine.replaceAll("'", "");
                out.write(nextLine.getBytes());
                out.write("\n".getBytes());
            }

            return new InputStreamReader(new ByteArrayInputStream(out.toByteArray()));
        } catch (Exception e) {
            in.close();
            fis.close();
            this.logger.error("Problem at replaceBackSlashes", e);
        }
        throw new Exception();
    }

Answer 1

Do not use a CSV parser to parse TSV inputs. It will break if the TSV has fields with a quote character, for example.

uniVocity-parsers comes with a TSV parser. You can parse a billion rows without problems.

Example to parse a TSV input:

TsvParserSettings settings = new TsvParserSettings();
TsvParser parser = new TsvParser(settings);

// parses all rows in one go.
List<String[]> allRows = parser.parseAll(new FileReader(yourFile));

If your input is so big it can't be kept in memory, do this:

TsvParserSettings settings = new TsvParserSettings();

// all rows parsed from your input will be sent to this processor
ObjectRowProcessor rowProcessor = new ObjectRowProcessor() {
    @Override
    public void rowProcessed(Object[] row, ParsingContext context) {
        //here is the row. Let's just print it.
        System.out.println(Arrays.toString(row));
    }
};
// the ObjectRowProcessor supports conversions from String to whatever you need:
// converts values in columns 2 and 5 to BigDecimal
rowProcessor.convertIndexes(Conversions.toBigDecimal()).set(2, 5);

// converts the values in columns "Description" and "Model". Applies trim and to lowercase to the values in these columns.
rowProcessor.convertFields(Conversions.trim(), Conversions.toLowerCase()).set("Description", "Model");

//configures to use the RowProcessor
settings.setRowProcessor(rowProcessor);

TsvParser parser = new TsvParser(settings);
//parses everything. All rows will be pumped into your RowProcessor.
parser.parse(new FileReader(yourFile));

Disclosure: I am the author of this library. It's open-source and free (Apache V2.0 license).