How to split a comma separated String while ignoring escaped commas?

Question

I need to write a extended version of the StringUtils.commaDelimitedListToStringArray function which gets an additional parameter: the escape char.

so calling my:

commaDelimitedListToStringArray("test,test\\,test\\,test,test", "\\")

should return:

["test", "test,test,test", "test"]

My current attempt is to use String.split() to split the String using regular expressions:

String[] array = str.split("[^\\\\],");

But the returned array is:

["tes", "test\,test\,tes", "test"]

Any ideas?

Answer 1

Try:

String array[] = str.split("(?<!\\\\),");

Basically this is saying split on a comma, except where that comma is preceded by two backslashes. This is called a negative lookbehind zero-width assertion.

Answer 2

Don't reinvent the wheel.

Answer 3

The regular expression

[^\\],

means "match a character which is not a backslash followed by a comma" - this is why patterns such as t, are matching, because t is a character which is not a backslash.

I think you need to use some sort of negative lookbehind, to capture a , which is not preceded by a \ without capturing the preceding character, something like

(?<!\\),

(BTW, note that I have purposefully not doubly-escaped the backslashes to make this more readable)

Answer 4

For future reference, here is the complete method i ended up with:

public static String[] commaDelimitedListToStringArray(String str, String escapeChar) {
    // these characters need to be escaped in a regular expression
    String regularExpressionSpecialChars = "/.*+?|()[]{}\\";

    String escapedEscapeChar = escapeChar;

    // if the escape char for our comma separated list needs to be escaped 
    // for the regular expression, escape it using the \ char
    if(regularExpressionSpecialChars.indexOf(escapeChar) != -1) 
        escapedEscapeChar = "\\" + escapeChar;

    // see http://stackoverflow.com/questions/820172/how-to-split-a-comma-separated-string-while-ignoring-escaped-commas
    String[] temp = str.split("(?<!" + escapedEscapeChar + "),", -1);

    // remove the escapeChar for the end result
    String[] result = new String[temp.length];
    for(int i=0; i<temp.length; i++) {
        result[i] = temp[i].replaceAll(escapedEscapeChar + ",", ",");
    }

    return result;
}