Question

I’m not strong in regex, so any help would be appreciated.

I need to parse such strings:

["text", "text", ["text",["text"]],"text"]

And output should be (4 strings):

text, text, ["text",["text"]], text

I’ve tried this pattern (\\[[^\\[,^\\]]*\\])|(\"([^\"]*)\"):

String data="\"aa\", \"aaa\", [\"bb\", [\"1\",\"2\"]], [cc]";
Pattern p=Pattern.compile("(\\[[^\\[,^\\]]*\\])|(\"([^\"]*)\")");

But output is (quotes themselves in output are not so critical):

"aa", "aaa", "bb", "1", "2", [cc]

How to improve my regex?

Answer 1

I’m not sure regex are able to do that kind of stuff on their own. Here is a way to do it though:

// data string
String input = "\"aa\", \"a, aa\", [\"bb\", [\"1\", \"2\"]], [cc], [\"dd\", [\"5\"]]";
System.out.println(input);

// char that can't ever be within the data string
char tempReplacement = '#';
// escape strings containing commas, e.g "hello, world", ["x, y", 42]
while(input.matches(".*\"[^\"\\[\\]]+,[^\"\\[\\]]+\".*")) {
    input = input.replaceAll("(\"[^\"\\[\\]]+),([^\"\\[\\]]+\")", "$1" + tempReplacement + "$2");
}
// while there are "[*,*]" substrings
while(input.matches(".*\\[[^\\]]+,[^\\]]+\\].*")) {
    // replace the nested "," chars by the replacement char
    input = input.replaceAll("(\\[[^\\]]+),([^\\]]+\\])", "$1" + tempReplacement + "$2");
}

// split the string by the remaining "," (i.e. those non nested)
String[] split = input.split(",");

List<String> output = new LinkedList<String>();
for(String s : split) {
    // replace all the replacement chars by a ","
    s = s.replaceAll(tempReplacement + "", ",");
    s = s.trim();
    output.add(s);
}

// syso
System.out.println("SPLIT:");
for(String s : output) {
    System.out.println("\t" + s);
}

Output:

"aa", "a, aa", ["bb", ["1", "2"]], [cc], ["dd", ["5"]]
SPLIT:
    "aa"
    "a, aa"
    ["bb", ["1","2"]]
    [cc]
    ["dd", ["5"]]

PS: the code seems complex ’cause commented. Here is a more concise version:

public static List<String> split(String input, char tempReplacement) {
    while(input.matches(".*\"[^\"\\[\\]]+,[^\"\\[\\]]+\".*")) {
        input = input.replaceAll("(\"[^\"\\[\\]]+),([^\"\\[\\]]+\")", "$1" + tempReplacement + "$2");
    }
    while(input.matches(".*\\[[^\\]]+,[^\\]]+\\].*")) {
        input = input.replaceAll("(\\[[^\\]]+),([^\\]]+\\])", "$1" + tempReplacement + "$2");
    }
    String[] split = input.split(",");
    List<String> output = new LinkedList<String>();
    for(String s : split) {
        output.add(s.replaceAll(tempReplacement + "", ",").trim());
    }
    return output;
}

Call:

String input = "\"aa\", \"a, aa\", [\"bb\", [\"1\", \"2\"]], [cc], [\"dd\", [\"5\"]]";
List<String> output = split(input, '#');