^M characters showing in CSV file generated using opencsv.CSVWriter

Csv writing Code

private void writeReversalPendingCsv(List<String[]> elements) throws IOException {
	BufferedWriter writer = null;
	CSVWriter csvWriter = null;
	String fileName = null;
    ..
    writer = new BufferedWriter(new FileWriter(filePath));
			Character sep = new Character('|');
			csvWriter = new CSVWriter(writer,
					sep,
					new Character('
private void writeReversalPendingCsv(List<String[]> elements) throws IOException {
BufferedWriter writer = null;
CSVWriter csvWriter = null;
String fileName = null;
..
writer = new BufferedWriter(new FileWriter(filePath));
Character sep = new Character('|');
csvWriter = new CSVWriter(writer,
sep,
new Character('\0'),
CSVWriter.DEFAULT_ESCAPE_CHARACTER,
CSVWriter.DEFAULT_LINE_END);
for (String[] row : elements) {
csvWriter.writeNext(row);
}
'),
					CSVWriter.DEFAULT_ESCAPE_CHARACTER,
					CSVWriter.DEFAULT_LINE_END);
            for (String[] row : elements) {
			     csvWriter.writeNext(row);
		    }

Csv in vim mode -

2|value|hello^M
2|value2|hello2

CSV reading

Before this writing part, I also read a csv of the same format.

Scanner scanner = new Scanner(file.getInputStream());
			List<String[]> reversalPending = new ArrayList<>();
			scanner.useDelimiter("\\n");
			int totalRows = 0;
			while (scanner.hasNext()) {
                   ..
                   String line = scanner.next();
				   String[] arr = line.split("\\|");
                   .. processing 
                   if(processing fails) {
                       reversalPending.add(arr);
                       writeReversalPendingCsv(reversalPending);
                   }
            }

I process each row and depending on some condition, take these rows and write them into a csv file.

So, my overall logic is -

• read csv file
• process each row
• dump unprocessed rows into csv file.

If I use the csv file from output of csv writing and feed in the same flow, the processing works but I get an extra ^M -

2|value|hello^M^M
2|value2|hello2

Should I prevent this? How, if so?

in vim ^M is used to display \r carriage return character (see this for other "weird looking characters").

\r\n is used by windows as "line ending", while unix uses just \n.

what is happening here is that your input file uses \r\n as line ending, the \r is not getting "eaten" by Scanner and ends up in the strings because you specify only \n as delimiter.

setting \r\n as delimiter fixes the issue or better \r?\n since input of useDelimiter() is a regex, ? after \r means that \r is optional and in this way it will work properly with both files written from windows and files written from unix-like systems.

scanner.useDelimiter("\r?\n");