Supercsv Append Rather Than Overwrite?

Is it possible to add new lines to a CSV file, rather than overwrite the last one? Here is my method I call when I want to add a new line: private static void writeWithCsvMapWriter

Solution 1:

Add true to the parameters in new FileWriter:

mapWriter = new CsvMapWriter(new FileWriter(".../writeWithCsvMapWriter.csv", true), CsvPreference.STANDARD_PREFERENCE);

Solution 2:

As frickskit pointed out: the trick is to add true as the second parameter of new FileWriter(), but this will add the header underneath existing rows again as well. Use something in the lines of the following to check for the existence of a header in an existing file first before you decide to write it out.

publicvoidwrite(String fileName, List<Map<String, String>> lines)throws IOException {
    final String[] HEADER = newString[] {
        "Column1",
        "Column2",
        "Column3"
    };

    booleanwriteHeader=true;

    try (ICsvMapReadermapReader=newCsvMapReader(newFileReader(fileName), CsvPreference.STANDARD_PREFERENCE)) {

        final String[] existingHeader = mapReader.getHeader(true);

        if (Arrays.equals(existingHeader, HEADER)) {
            writeHeader = false;
        }
    } catch (FileNotFoundException ex) {}

    try (ICsvMapWritermapWriter=newCsvMapWriter(newFileWriter(fileName, true), CsvPreference.STANDARD_PREFERENCE)) {

        final CellProcessor[] processors = getProcessors();

        if (writeHeader) {
            mapWriter.writeHeader(HEADER);
        }

        for (Map<String, String> entry : lines) {
            mapWriter.write(entry, HEADER, processors);
        }
    }
}