Recursive object write to flat csv file

Question

I need to write object such

class User {
    UUID id;
    String name;
    Role role;
}

class Role {
    String name;
    LocalDate activeFrom;
    Authority owner;
}

class Authority {
    String name;
}

The tricky think is that csv writing should work recursively throught objects tree. Also need to write LocalDate as a String like 2019-11-05 f.e.;

The resulting csv file should be flat and looks like:

user.id,user.name,user.role.name,user.role.activeFrom,user.role.owner.name

// example values

---

I've tried already OpenCsv:

        StatefulBeanToCsv<User> beanToCsv = new StatefulBeanToCsvBuilder<User>(printWriter).build();
        try {
            beanToCsv.write(users);
        } catch (CsvDataTypeMismatchException | CsvRequiredFieldEmptyException e) {
            e.printStackTrace();
        }
        printWriter.close();

and Univocity parsers:

CsvWriterSettings settings = new CsvWriterSettings();
        ObjectRowWriterProcessor processor = new ObjectRowWriterProcessor();
        settings.setRowWriterProcessor(processor);
        processor.convertType(User.class, );

No luck so far. They can serialize to csv only top level object. Also in OpenCsv I had issue to serialize LocalDate. Can You help me? Advise approach or library?

Answer 1

As I did not get any answer, I will describe my solution. I used library:

http://super-csv.github.io/super-csv/index.html

and extension:

https://super-csv.github.io/super-csv/dozer.html

Code:

import org.supercsv.io.dozer.CsvDozerBeanWriter;
import org.supercsv.prefs.CsvPreference;
import java.io.IOException;
import java.io.Writer;

static final String[] FIELD_MAPPING = new String[]{
    "user.id", "user.name", "user.role.name", "user.role.activeFrom", "user.role.owner.name"
};

    try (var beanWriter = new CsvDozerBeanWriter(printWriter, CsvPreference.STANDARD_PREFERENCE)) {
        beanWriter.configureBeanMapping(User.class, FIELD_MAPPING);
        beanWriter.writeHeader(FIELD_MAPPING);
        for (User user : users) {
            beanWriter.write(user);
        }
    }
    printWriter.close();

https://super-csv.github.io/super-csv/xref-test/org/supercsv/example/dozer/Writing.html

And how You can test it:

@Test
void status_written_in_csv_format() {
    // Setup
    WriteCsvToResponse objectUnderTest = new WriteCsvToResponse ();
    StringWriter stringWriter = new StringWriter();
    PrintWriter printWriter = new PrintWriter(stringWriter);

    // Given
    Status status = ...

    // When
    objectUnderTest.writeStatus(printWriter, status);

    // Then
    String actualCsv = stringWriter.toString();
    assertThat(actualCsv.split("\n"))
       .as("Produced CSV")
       .containsExactly(
         "id,storeId,status",
         "42,142,OK");
}

How to test a method using a PrintWriter?

Answer 2

On univocity-parsers, without any mappings, you can simply annotate the nested objects with @Nested and it will work.

class User {
    ...

    @Nested
    Role role;
}