How to find out which line separator BufferedReader#readLine() used to split the line?

Question

I am reading a file via the BufferedReader

String filename = ...
br = new BufferedReader( new FileInputStream(filename));
while (true) {
   String s = br.readLine();
   if (s == null) break;
   ...
}

I need to know if the lines are separated by '\n' or '\r\n' is there way I can find out ?

I don't want to open the FileInputStream so to scan it initially. Ideally I would like to ask the BufferedReader since it must know.

I am happy to override the BufferedReader to hack it but I really don't want to open the filestream twice.

Thanks,

Note: the current line separator (returned by System.getProperty("line.separator") ) can not be used as the file could have been written by another app on another operating system.

Answer 1

To be in phase with the BufferedReader class, you may use the following method that handles \n, \r, \n\r and \r\n end line separators:

public static String retrieveLineSeparator(File file) throws IOException {
    char current;
    String lineSeparator = "";
    FileInputStream fis = new FileInputStream(file);
    try {
        while (fis.available() > 0) {
            current = (char) fis.read();
            if ((current == '\n') || (current == '\r')) {
                lineSeparator += current;
                if (fis.available() > 0) {
                    char next = (char) fis.read();
                    if ((next != current)
                            && ((next == '\r') || (next == '\n'))) {
                        lineSeparator += next;
                    }
                }
                return lineSeparator;
            }
        }
    } finally {
        if (fis!=null) {
            fis.close();
        }
    }
    return null;
}

Answer 2

Maybe you could use Scanner instead.

You can pass regular expressions to Scanner#useDelimiter() to set custom delimiter.

String regex="(\r)?\n";
String filename=....;
Scanner scan = new Scanner(new FileInputStream(filename));
scan.useDelimiter(Pattern.compile(regex));
while (scan.hasNext()) {
    String str= scan.next();
    // todo
}

You could use this code below to convert BufferedReader to Scanner

 new Scanner(bufferedReader);