I try to generate a .csv file in Java using OpenCSV. I want to generate results without hardcoding.

I have an entity with has fields like: Id, Title, Overview, etc. In List movies I store all data from database.

I want to write this list in .csv without tell headers or other things.

Example.

...writeToCSV(Movie.class) not writeToCSV("ID", "Title', etc)

In first step, I used Apache POI, but he don't work properly.

@Slf4j
@Setter
@NoArgsConstructor
public class CSVHelper {
    private CSVFormat csvFormat;
    private PrintWriter printWriter;
    private CSVPrinter csvPrinter;


    public void writeHeader(Class<?> c) {
        List<String> headers = getHeaders(c);
        try {
            setCsvPrinter(new CSVPrinter(printWriter, csvFormat));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        headers.forEach(header -> {
            try {
                csvPrinter.print(header);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        });
    }

    public void writeToCsv(List<?> list, Class<?> c) {
        writeHeader(c);
        List<String> headers = getHeaders(c);
        try {
            setCsvPrinter(new CSVPrinter(printWriter, csvFormat));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        list.forEach(o -> {
            try {
                csvPrinter.println();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            headers.forEach(header -> {
                try {
                    Method method = c.getMethod("get"   header.substring(0, 1).toUpperCase()   header.substring(1));
                    String value = String.valueOf(method.invoke(o));
                    csvPrinter.print(value);

                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
            });
        });
    }

    private static List<String> getHeaders(Class<?> c) {
        List<Field> fields = List.of(c.getDeclaredFields());
        return fields.stream().map(Field::getName).collect(Collectors.toList());
    }
}

I like to use direct object to method, without any code from me. This code is working but on any change to the entity it does't work.

CodePudding user response：

From the documentation:

The easiest way to write CSV files will in most cases be StatefulBeanToCsv, which is simplest to create with StatefulBeanToCsvBuilder, and which is thus named because there used to be a BeanToCsv.Thankfully, no more.

 // List<MyBean> beans comes from somewhere earlier in your code.
 Writer writer = new FileWriter("yourfile.csv");
 StatefulBeanToCsv beanToCsv = new StatefulBeanToCsvBuilder(writer).build();
 beanToCsv.write(beans);
 writer.close();

Source: http://opencsv.sourceforge.net/#writing_from_a_list_of_beans