How to write bean to CSV using OpenCSV without converting to String[]?

Question

I have a large array of a bean that needs to be written to a CSV file. I am trying to use OpenCSV but all the examples I see on the web ask me to convert the bean (POJO) that I have to a string array. I don't want to do this since this would mean I will have to go through the million beans and convert each of those beans to String[] which would be a very memory-expensive process.

This is the piece of code I have right now for doing this:

private static void writeRowsToCsv(Path filePath, List<MyBean> rows)
        throws IOException {

    StringWriter writer = new StringWriter();
    CSVWriter csvWriter = new CSVWriter(writer, '#', '\'');
    ColumnPositionMappingStrategy mappingStrategy =
            new ColumnPositionMappingStrategy();
    mappingStrategy.setType(MyBean.class);
    List<String[]> rowsInStringArray = convertBeanToStringArray(rows)
    csvWriter.writeAll(rowsInStringArray);
}

Is there a way I can avoid the conversion to String[] and use the list of beans that I have to write to a CSV file?

Solution 1

You call writeNext() in a loop, converting one bean at a time. Not memory-expensive at all.

Solution 2

Jobin, seriously, if you are using OpenCSV then use the BeanToCsv or the newer StatefulBeanToCsv. It will save your sanity.

private static void writeRowsToCsv(Path filePath, List<MyBean> rows)
        throws IOException {

    StringWriter writer = new StringWriter();
    ColumnPositionMappingStrategy mappingStrategy =
            new ColumnPositionMappingStrategy();
    mappingStrategy.setType(MyBean.class);

    StatefulBeanToCsvBuilder<MyBean> builder = new StatefulBeanToCsvBuilder(writer);
    StatefulBeanToCsv beanWriter = builder
              .withMappingStrategy(mappingStrategy)
              .withSeparator('#')
              .withQuotechar('\'')
              .build();

    beanWriter.write(rows);
}

Comments

[ledlogic]

The constructor StatefulBeanToCsvBuilder(CSVWriter) does not exist.

[Scott Conway]

ledlogic - you are absolutely correct. I corrected my code example above as the StatefulBeanToCsv creates a CSVWriter based on values passed in from the builder but it does not take a CSVWriter directly. Not exactly sure what I was thinking back in May but thank you for pointing that out because who knows how long that would have stayed there.

[Bharath]

this is the easier way to do it.