Parsing comma-separated values containing quoted commas and newlines

Question

I have string with some special characters. The aim is to retrieve String[] of each line (, separated) You have special character “ where you can have /n and ,

Answer 1

Try this:

String source = "Alpha,Beta,Gama,\"23-5-2013,TOM\",TOTO,\"Julie, KameL\n"
              + "Titi\",God,\" timmy, tomy,tony,\n"
              + "tini\".";

Pattern p = Pattern.compile("(([^\"][^,]*)|\"([^\"]*)\"),?");
Matcher m = p.matcher(source);

while(m.find())
{
    if(m.group(2) != null)
        System.out.println( m.group(2).replace("\n", "") );
    else if(m.group(3) != null)
        System.out.println( m.group(3).replace("\n", "") );
}

If it matches a string without quotes, the result is returned in group 2. Strings with quotes are returned in group 3. Hence i needed a distinction in the while-block. You might find a prettier way.

Output:
Alpha
Beta
Gama
23-5-2013,TOM
TOTO
Julie, KameLTiti
God
timmy, tomy,tony,tini
.

Answer 2

Description

Consider the following powershell example of a universal regex tested on a Java parser which requires no extra processing to reassemble the data parts. The first matching group will match a quote, then carry that to the end of the match so that you're assured to capture the entire value between but not including the quotes. I also don't capture the commas unless they were embedded a quote delimited substring.

(?:^|,\s{0,})(["]?)\s{0,}((?:.|\n|\r)*?)\1(?=[,]\s{0,}|$)

Example

$Matches = @()
$String = 'Alpha,Beta,Gama,"23-5-2013,TOM",TOTO,"Julie, KameL\n
Titi",God,"timmy, \n
tomy,tony,tini"'
$Regex = '(?:^|,\s{0,})(["]?)\s{0,}((?:.|\n|\r)*?)\1(?=[,]\s{0,}|$)'

Write-Host start with 
write-host $String
Write-Host
Write-Host found
([regex]"(?i)(?m)$Regex").matches($String) | foreach {
    write-host "key at $($_.Groups[1].Index) = '$($_.Groups[1].Value)'`t= value at $($_.Groups[2].Index) = '$($_.Groups[2].Value)'"
    } # next match

Yields

start with
Alpha,Beta,Gama,"23-5-2013,TOM",TOTO,"Julie, KameL\n
Titi",God,"timmy, \n
tomy,tony,tini"

found
key at 0 = ''   = value at 0 = 'Alpha'
key at 6 = ''   = value at 6 = 'Beta'
key at 11 = ''  = value at 11 = 'Gama'
key at 16 = '"' = value at 17 = '23-5-2013,TOM'
key at 32 = ''  = value at 32 = 'TOTO'
key at 37 = '"' = value at 38 = 'Julie, KameL\n
Titi'
key at 60 = ''  = value at 60 = 'God'
key at 64 = '"' = value at 65 = 'timmy, \n
tomy,tony,tini'

Summary

• (?: start non capture group
• ^ require start of string
• | or
• ,\s{0,} a comma followed by any number of white space
• ) close the non capture group
• ( start capture group 1
• ["]? consume a quote if it exists, I like doing it this way incase you want to include other characters then a quote
• ) close capture group 1
• \s{0,} consume any spaces if they exist, this means you don't need to trim the value later
• ( start capture group 2
• (?:.|\n|\r)*? capture all characters including a new line, non greedy
• ) close capture group 2
• \1 if there was a quote it would be stored in group 1, so if there was one then require it here
• (?= start zero assertion look ahead
• [,]\s{0,} must have a comma followed by optional whitespace
• | or
• $ end of the string
• ) close the zero assertion look ahead

Answer 3

See this related answer for a decent Java-compatible regex for parsing CSV.

It recognizes:

• Newlines (after values or inside quoted values)
• Quoted values containing escaped double-quotes like ""this""

In short, you will use this pattern: (?:,|\n|^)("(?:(?:"")*[^"]*)*"|[^",\n]*|(?:\n|$))

Then collect each Matcher group(1) in a find() loop.

---

Note: Although I have posted this answer here about a "decent" regex I discovered, just to save people searching for one, it is by no means robust. I still agree with this answer by user "fgv": a CSV Parser is preferrable.

Answer 4

Parsing CSV is a whole lot harder than one would imagine at first sight, and that's why your best option is to use a well-designed and tested library to do that work for you. Two libraries are opencsv and supercsv, and many others. Have a look at both and use the one that's the best fit to your requirements and style.