SuperCSV append rather than overwrite?

问题

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() throws Exception 
{
    final String[] header = new String[] { "Engineer", "Time/Date", "Project", "Test ID", "Data Centre", "Data Hall", "Row", "Grille", "I/S" };

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd_HH:mm:ss");
    String currentDateandTime = sdf.format(new Date());

    final Map<String, Object> NewRow = new HashMap<String, Object>();
    NewRow.put(header[0], Name.getText().toString());
    NewRow.put(header[1], currentDateandTime);
    NewRow.put(header[2], "Expect");
    NewRow.put(header[3], TestID.getText());
    NewRow.put(header[4], DataCentre.getText());
    NewRow.put(header[5], DataHall.getText());
    NewRow.put(header[6], Row.getText());
    NewRow.put(header[7], Grille.getText());
    NewRow.put(header[8], IS.getText());

    ICsvMapWriter mapWriter = null;

    try 
    {
        mapWriter = new CsvMapWriter(new FileWriter("data/data/" + PACKAGE_NAME +"/writeWithCsvMapWriter.csv"), CsvPreference.STANDARD_PREFERENCE);

        final CellProcessor[] processors = getProcessors();

        mapWriter.writeHeader(header);
        mapWriter.write(NewRow, header, processors);  
    }
    finally 
    {
        if( mapWriter != null ) 
        {
            mapWriter.close();
        }
    }
}

Thanks

回答1:

Add true to the parameters in new FileWriter:

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

回答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.

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

    boolean writeHeader = true;

    try (ICsvMapReader mapReader = new CsvMapReader(new FileReader(fileName), CsvPreference.STANDARD_PREFERENCE)) {

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

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

    try (ICsvMapWriter mapWriter = new CsvMapWriter(new FileWriter(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);
        }
    }
}

来源：https://stackoverflow.com/questions/15729977/supercsv-append-rather-than-overwrite

标签

java

android

csv

supercsv