Using builder to create nested XML

Question

I'm using the Jackson set of classes to read in a CSV file, and convert it to xml, but need some advice on how to add a nested value.

The code I'm using is:

  package reader;

  import java.io.File;
  import java.io.IOException;
  import java.util.List;
  import java.util.Map;

  import com.fasterxml.jackson.databind.MappingIterator;
  import com.fasterxml.jackson.dataformat.csv.CsvMapper;
  import com.fasterxml.jackson.dataformat.csv.CsvSchema;
  import com.fasterxml.jackson.dataformat.xml.XmlMapper;

  public class Mustang
  {

public static void main(String[] args) throws Exception
{

    // Define the input file
    File input = new File("c:\\temp\\all_idocs.csv");
    // Define the output file
    File output = new File("c:\\temp\\all_idocs.xml");

    System.out.println("INFO: Commencing Conversion");

    List<Map<?, ?>> data = readObjectsFromCsv(input); // readObjectsFromCSV(input
                                                        // file name)

    System.out.println(readObjectsFromCsv(input));

    writeAsXml(data, output); // writeAsXml function, to output location

    System.out.println("INFO: Conversion Complete");

}

public static List<Map<?, ?>> readObjectsFromCsv(File file)
        throws IOException
{
    CsvSchema schema = CsvSchema.builder()  
            .addColumn("A0001")
            .addColumn("A0186")
            .addColumn("A0187")
            .addColumn("A0352")
            .addColumn("A0539")
            .addColumn("A0963")
            .addColumn("A1046")
            .addColumn("A0792")
            .addColumn("A0218")
            .addColumn("A0584")
            .addColumn("A0016")
            .addColumn("A0017")
            .addColumn("A0478")
            .addColumn("A0051")
            .addColumn("A0052")
            .addColumn("A0053")
            .addColumn("A0059")
            .addColumn("A0440")
            .addColumn("A0054")
            .addColumn("A0055")
            .addColumn("A0056")
            .addColumn("A0057")
            .addColumn("A0058")
            .addColumn("A1128")
            .addColumn("A0003")
            .addColumn("A0069")
            .addColumn("A0070")
            .addColumn("A0074")
            .addColumn("A0073")
            .addColumn("A0071")
            .addColumn("A0110")
            .addColumn("A0109")
            .addColumn("A0108")
            .build();

    CsvMapper csvMapper = new CsvMapper();
    MappingIterator<Map<?, ?>> mappingIterator = csvMapper
            .reader(Map.class).with(schema).readValues(file);  // Change the "with()" to pull in the schema

    return mappingIterator.readAll();
}

public static void writeAsXml(List<Map<?, ?>> data, File file)
        throws IOException
{
    XmlMapper mapper = new XmlMapper();
    mapper.writeValue(file, data);
}

}

If I run this against a CSV file, I get output similar to this:

<item>
    <A0001>J1000097</A0001>
    <A0186>5028197000004</A0186>
    <A0187>1</A0187>
    <A0352></A0352>
    <A0539>00</A0539>
    <A0963>20050209</A0963>
</item>

I want to see if it's possible to indent/nest some of these attributes, to produce something like this:

<item>
    <A0001>J1000097</A0001>
    <A0186>5028197000004</A0186>
    <A0187>
        <A0352>12</A0352>
        <A0539>00</A0539>
    </A0187>
    <A0963>20050209</A0963>
</item>

I'm assuming I must have to do something within the builder section of the code, but as I'm new to using it, I can't fathom out how.

Answer 1

In this case you may want to process Map after reading it from CSV, but before writing it as XML. You can then add a wrapper around values you want to group. That is, something like:

Map<?,?> value = ... ; // individual row
Map<String,Object> wrapped = new LinkedHashMap<>();
wrapped.put("A0352", value.remove("A0352"));
wrapped.put("A0539", value.remove("A0539"));
value.put("A0187", wrapped);

another possibility would be to use value conversion between Map, and POJO type that uses @JsonUnwrapped to handle grouping. Conversion itself may be done using:

MyPOJO value = mapper.convertValue(map, MyPOJO.class); // and/or reverse

but this approach may become more complicated.