How to write ArrayList<Object> to a csv file

Question

I have a ArrayList<Metadata> and i want to know if there is a Java API for working with CSV files which has a write method which accepts a ArrayList<> as parameter similar to LinqToCsv in .Net. As i know OpenCSV is available but the CsvWriter class doesn't accept a collection. My Metadata Class is

public class Metadata{
    private String page;
    private String document;
    private String loan;
    private String type;
}

ArrayList<Metadata> record = new ArrayList<Metadata>();

once i populate the record, i want to write each row into a csv file. Please suggest.

Answer 1

Surely there'll be a heap of APIs that will do this for you, but why not do it yourself for such a simple case? It will save you a dependency, which is a good thing for any project of any size.

Create a toCsvRow() method in Metadata that joins the strings separated by a comma.

public String toCsvRow() {
    return Stream.of(page, document, loan, type)
            .map(value -> value.replaceAll("\"", "\"\""))
            .map(value -> Stream.of("\"", ",").anyMatch(value::contains) ? "\"" + value + "\"" : value)
            .collect(Collectors.joining(","));
}

Collect the result of this method for every Metadata object separated by a new line.

String recordAsCsv = record.stream()
        .map(Metadata::toCsvRow)
        .collect(Collectors.joining(System.getProperty("line.separator")));

---

EDIT Should you not be so fortunate as to have Java 8 and the Stream API at your disposal, this would be almost as simple using a traditional List.

public String toCsvRow() {
    String csvRow = "";
    for (String value : Arrays.asList(page, document, loan, type)) {
        String processed = value;
        if (value.contains("\"") || value.contains(",")) {
            processed = "\"" + value.replaceAll("\"", "\"\"") + "\"";
        }
        csvRow += "," + processed;
    }
    return csvRow.substring(1);
}

Answer 2

通过使用CSVWriter ，您可以将ArrayList转换为数组，并将其传递给writer。

csvWriter.writeNext(record.toArray(new String[record.size()]));

Answer 3

If you have an ArrayList of Objects (Metadata in your case) you would use the BeanToCSV instead of the CSVWriter.

You can look at the BeanToCSVTest in the opencsv source code for examples of how to use it.