Java character escaping

Question

While I was programming I found weird behavior for the java String. I am trying to parse a string as command with arguments:

Below is a screenshot of the variables during debug.

This is my code to read the command:

public List<String> readCommand(Sender sender, String command) {
    boolean isInQuote = false;
    List<String> splits = new ArrayList();
    String current = "";
    char[] arr = command.toCharArray();
    for (int i = 0; i < command.toCharArray().length; i++) {
        char c = arr[i];
        if (c == '"') {
        isInQuote = !isInQuote;

        if (!isInQuote) {
            splits.add(current);
            current = "";
        }
        }

        if (isInQuote) {
        current += c;
        } else {
        if (c == ' ' || i == arr.length - 1) {
            if (i == arr.length - 1) {
            current += c;
            }
            splits.add(current);
            current = "";
        } else {
            current += c;
        }
        }
    }

    return splits;
    }

As expected in the tests; the string should be parsed as:

1. "this"
2. "is a test"
3. "now"

instead it is parsed as:

1. "this"
2. "\"is a test"
3. "\""
4. "now"

Why don't the escaped quotes work and what am I doing wrong?

P.S.: I would try to research this subject but I don't know how to call this. Argument parsing with quotes...?

UPDATE: After your help, I discovered another bug which I fixed. The code is fully working now. All that is left now is to remake it :). The \" not working really confused me. http://pastebin.com/AdBUqJvH

Answer 1

First let's simplify your current attempt with:

public static void main(String[] args) throws Exception {
    String data = "this \"is a test\" now \"hello\" goodbye";

    List<String> splits = new ArrayList();
    String current = "";
    boolean inQuote = false;        
    for (int i = 0; i < data.length(); i++) {
        if (data.charAt(i) == ' ' && !inQuote) {
            // Add your current split word and move on to the next character
            splits.add(current);
            current = "";
            continue; 
        } else if (data.charAt(i) == '\"') {
            // Flip the flag whenever you run across a quotation mark
            inQuote = !inQuote;
        }

        // Add current character to string, spaces never get added
        current += data.charAt(i);
    }
    // Add remaining split data from hitting the end of data
    if (!current.isEmpty()) {
        splits.add(current);
    }

    // Display results
    for (String split : splits) {
        System.out.println(split);
    }
}

Results:

this
"is a test"
now
"hello"
goodbye

Regex

Then you can shorten your code with Regex with the following (and the results are the same):

public static void main(String[] args) throws Exception {
    String data = "this \"is a test\" now \"hello\" goodbye";

    Matcher matcher = Pattern.compile("[^\\s\"']+|\"[^\"]*\"|'[^']*'").matcher(data);
    while (matcher.find()) {
        System.out.println(matcher.group());
    }
}

Answer 2

Your code works fine for me . except that the out put is

this "is a test" " now

instead of

this "is a test" now

I made a small change for that

you said you don't the input doesn't always contains '"', but you are hard coding it with '"', so may be the answer by [Igor Sadovnikov] is better?

    public static void main(String[] args) {
        String s = "this \"is a test\" now";
        List<String> commands = readCommand(null, s);
        for (String command : commands) {
            System.out.print(command + " ");
        }
    }

    private static List<String> readCommand(Object sender, String command) {
        boolean isInQuote = false;
        List<String> splits = new ArrayList<String>();
        String current = "";
        char[] arr = command.toCharArray();
        for (int i = 0; i < command.toCharArray().length; i++) {
            char c = arr[i];
            if (c == '"') {
                isInQuote = !isInQuote;

                if (!isInQuote) {
                    //CHANGE HERE  ... added + c
                    splits.add(current + c);
                    current = "";
                }
            }

            if (isInQuote) {
                current += c;
            } else {
                if (c == ' ' || i == arr.length - 1) {
                    if (i == arr.length - 1) {
                        current += c;
                    }
                    splits.add(current);
                    current = "";
                } 
                // --- CHANGE HERE
                else if (c != '"') {
                    current += c;
                }
            }
        }

        return splits;
    }

Answer 3

This is solution for your task.

public static void main(String[] args) {
    List<String> splits = readCommand("this \"is a\" test\" now");
    for(String str : splits) {
            System.out.println("_"+str+"_");
    }
}

public static List<String> readCommand(String command) {
    List<String> list = Arrays.asList(command.split("\""));
    List<String> list2 = new ArrayList<>();
    for(String str : list) {
        str = checkFirst(str);
        str = checkLast(str);
        list2.add(str);
    }
    return list2;
}

private static String checkFirst(String str) {
    if (str.charAt(0) == ' ') {
        str = checkFirst(str.substring(1));
    }
    return str;
}

private static String checkLast(String str) {
    if (str.charAt(str.length() - 1) == ' ') {
        str = checkLast(str.substring(0, str.length() - 1));
    }
    return str;
}