Write CSV from List of HashMaps with Header using Apache Commons CSV

Question

I have to take an ArrayList of HashMap and create a CSV using Apache Commons CSV. However, it's not writing the values to the right headers. Is there an easy way to have the library automatically place the values to the right headers using the Enum? I don't want to manually assign it as I will be adding more columns.

This is what it's producing:

Here is what I have:

Header.java

public enum Header
{
    FIRST_NAME(),
    LAST_NAME(),
    GENDER();
}

Main

public static void main(String[] args)
{
    List<Map<Header, String>> output = new ArrayList<>();

    Map<Header, String> map = new HashMap<>();
    map.put(Header.FIRST_NAME, "John");
    map.put(Header.LAST_NAME, "Andrew");
    map.put(Header.GENDER, "Male");
    output.add(map);

    Map<Header, String> map2 = new HashMap<>();
    map2.put(Header.FIRST_NAME, "Sally");
    map2.put(Header.LAST_NAME, "Andrew");
    map2.put(Header.GENDER, "Female");
    output.add(map2);

    String outputFile = System.getProperty("java.io.tmpdir")+"test.csv";

    try (
            BufferedWriter writer = Files.newBufferedWriter(Paths.get(outputFile));
            CSVPrinter csvPrinter = new CSVPrinter(writer, CSVFormat.DEFAULT
                    .withHeader(Header.class));)
    {
        csvPrinter.printRecords(output);
        csvPrinter.flush();
    } catch (IOException ex)
    {
        Logger.getLogger(TestCSV.class.getName()).log(Level.SEVERE, null, ex);
    }

}

you man want to use jackson csv or open csv to read csv as java pojo, so you don't have to declare more enums — Holm
– Holm, Commented Mar 15, 2019 at 16:31
Not sure what you mean, as I want to specifically define the headers — trilogy
– trilogy, Commented Mar 15, 2019 at 16:40

Not a JD · Accepted Answer · 2019-03-15 16:36:28Z

4

How about this:

try (BufferedWriter writer = Files.newBufferedWriter(Paths.get(outputFile));
        CSVPrinter csvPrinter = new CSVPrinter(writer, CSVFormat.DEFAULT.withHeader(Header.class));) {
    for (Map<Header, String> row : output) {
        csvPrinter.printRecord(Arrays.asList(Header.values())
                                     .stream()
                                     .map(header -> row.get(header))
                                     .collect(Collectors.toList()));
    }
} catch (IOException ex) {
    Logger.getLogger(TestCSV.class.getName())
          .log(Level.SEVERE, null, ex);
}

answered Mar 15, 2019 at 16:36

Not a JD

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1 Comment

trilogy Over a year ago

Thanks, this looks even better than mine, as the order is taken from the Enum.

trilogy · Accepted Answer · 2019-03-15 16:36:36Z

1

Ok figured it out. I changed the maps to LinkedHashMap to retain order then did this:

   try (BufferedWriter writer = Files.newBufferedWriter(Paths.get(outputFile));
        CSVPrinter csvPrinter = new CSVPrinter(writer, CSVFormat.DEFAULT
        .withHeader(Header.class));)
   {

        for (Map<Header, String> val : output)
        {
            csvPrinter.printRecord(val.values().toArray());
        }

        csvPrinter.flush();

    } catch (IOException ex)
    {
        Logger.getLogger(TestCSV.class.getName()).log(Level.SEVERE, null, ex);
    }

answered Mar 15, 2019 at 16:36

trilogy

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