Parsing CSV input with a RegEx in java

Solution 1:

Operator precedence. Basically there is none. It's all left to right. So the or (|) is applying to the closing quote lookahead and the comma lookahead

Try:

(?:(?<=")([^"]*)(?="))|(?<=,|^)([^,]*)(?=,|$)

Solution 2:

(?:^|,)\s*(?:(?:(?=")"([^"].*?)")|(?:(?!")(.*?)))(?=,|$)

This should do what you want.

Explanation:

(?:^|,)\s*

The pattern should start with a , or beginning of string. Also, ignore all whitespace at the beginning.

Lookahead and see if the rest starts with a quote

(?:(?=")"([^"].*?)")

If it does, then match non-greedily till next quote.

(?:(?!")(.*?))

If it does not begin with a quote, then match non-greedily till next comma or end of string.

(?=,|$)

The pattern should end with a comma or end of string.

Solution 3:

When I started to understand what I had done wrong, I also started to understand how convoluted the lookarounds were making this. I finally realized that I didn't want all the matched text, I wanted specific groups inside of it. I ended up using something very similar to my original RegEx except that I didn't do a lookahead on the closing comma, which I think should be a little more efficient. Here is my final code.

package regex.parser;

import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class CSVParser {

    /*
     * This Pattern will match on either quoted text or text between commas, including
     * whitespace, and accounting for beginning and end of line.
     */
    private final Pattern csvPattern = Pattern.compile("\"([^\"]*)\"|(?<=,|^)([^,]*)(?:,|$)");  
    private ArrayList<String> allMatches = null;    
    private Matcher matcher = null;
    private String match = null;
    private int size;

    public CSVParser() {        
        allMatches = new ArrayList<String>();
        matcher = null;
        match = null;
    }

    public String[] parse(String csvLine) {
        matcher = csvPattern.matcher(csvLine);
        allMatches.clear();
        String match;
        while (matcher.find()) {
            match = matcher.group(1);
            if (match!=null) {
                allMatches.add(match);
            }
            else {
                allMatches.add(matcher.group(2));
            }
        }

        size = allMatches.size();       
        if (size > 0) {
            return allMatches.toArray(new String[size]);
        }
        else {
            return new String[0];
        }           
    }   

    public static void main(String[] args) {        
        String lineinput = "the quick,\"brown, fox jumps\",over,\"the\",,\"lazy dog\"";

        CSVParser myCSV = new CSVParser();
        System.out.println("Testing CSVParser with: \n " + lineinput);
        for (String s : myCSV.parse(lineinput)) {
            System.out.println(s);
        }
    }

}

Solution 4:

I know this isn't what the OP wants, but for other readers, one of the String.replace methods could be used to strip the quotes from each element in the result array of the OPs current regex.