Read CSV with Scanner()

Please stop writing faulty CSV parsers!

I've seen hundreds of CSV parsers and so called tutorials for them online.

Nearly every one of them gets it wrong!

This wouldn't be such a bad thing as it doesn't affect me but people who try to write CSV readers and get it wrong tend to write CSV writers, too. And get them wrong as well. And these ones I have to write parsers for.

Please keep in mind that CSV (in order of increasing not so obviousness):

1. can have quoting characters around values
2. can have other quoting characters than "
3. can even have other quoting characters than " and '
4. can have no quoting characters at all
5. can even have quoting characters on some values and none on others
6. can have other separators than , and ;
7. can have whitespace between seperators and (quoted) values
8. can have other charsets than ascii
9. should have the same number of values in each row, but doesn't always
10. can contain empty fields, either quoted: "foo","","bar" or not: "foo",,"bar"
11. can contain newlines in values
12. can not contain newlines in values if they are not delimited
13. can not contain newlines between values
14. can have the delimiting character within the value if properly escaped
15. does not use backslash to escape delimiters but...
16. uses the quoting character itself to escape it, e.g. Frodo's Ring will be 'Frodo''s Ring'
17. can have the quoting character at beginning or end of value, or even as only character ("foo""", """bar", """")
18. can even have the quoted character within the not quoted value; this one is not escaped

If you think this is obvious not a problem, then think again. I've seen every single one of these items implemented wrongly. Even in major software packages. (e.g. Office-Suites, CRM Systems)

There are good and correctly working out-of-the-box CSV readers and writers out there:

• opencsv
• Ostermiller Java Utilities
• Apache Commons CSV

If you insist on writing your own at least read the (very short) RFC for CSV.

scanner.useDelimiter(",");

This should work.

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;


public class TestScanner {

    public static void main(String[] args) throws FileNotFoundException {
        Scanner scanner = new Scanner(new File("/Users/pankaj/abc.csv"));
        scanner.useDelimiter(",");
        while(scanner.hasNext()){
            System.out.print(scanner.next()+"|");
        }
        scanner.close();
    }

}

For CSV File:

a,b,c d,e
1,2,3 4,5
X,Y,Z A,B

Output is:

a|b|c d|e
1|2|3 4|5
X|Y|Z A|B|

Scanner.next() does not read a newline but reads the next token, delimited by whitespace (by default, if useDelimiter() was not used to change the delimiter pattern). To read a line use Scanner.nextLine().

Once you read a single line you can use String.split(",") to separate the line into fields. This enables identification of lines that do not consist of the required number of fields. Using useDelimiter(","); would ignore the line-based structure of the file (each line consists of a list of fields separated by a comma). For example:

while (inputStream.hasNextLine())
{
    String line = inputStream.nextLine();
    String[] fields = line.split(",");
    if (fields.length >= 4) // At least one address specified.
    {
        for (String field: fields) System.out.print(field + "|");
        System.out.println();
    }
    else
    {
        System.err.println("Invalid record: " + line);
    }
}

As already mentioned, using a CSV library is recommended. For one, this (and useDelimiter(",") solution) will not correctly handle quoted identifiers containing , characters.