Ignore Specific Columns Parsing a CSV File with Jackson CSV

Question

My problem is that I need to parse CSV files with arbitrary columns/order into a known domain POJO (say Person). I can identify which columns that I need to process, ignoring the rest.

The option CsvParser.Feature.IGNORE_TRAILING_UNMAPPABLE" seemed to be exactly what I need, but the columns that I need to process are not necessarliy grouped at the start of the CSV file, and I cannot force the user to "re-order" the columns of their uploaded CSV files. Also, sometimes I do not get a header row, but the UI forces the user to identify columns & passes this information over.

For example, I have the following CSV file:

First Name,Last Name,Nickname,DOB,Occupation,Postal Code
Freddy,Benson,Ruprecht,08/14/45,Con Artist,76701
Lawrence,Jamieson,Prince,03/14/33,Con Artist,5201
Janet,Colgate,Jackal,03/13/55,Con Artist,90401

I only need 4 of the 6 columns (First Name, Last Name, DOB, Postal Code), as my Person POJO only includes those fields:

public class Person {
    private String firstName;
    private String lastName;
    private LocalDate dob;
    private String postalCode;
}

I have defined a CsvSchema typed for Person and specify the columns I'm interested in order (First Name, Last Name, IGNORE, DOB, IGNORE2, Postal Code), as I would like to skip columns (Nickname, Occupation). Hoever, the "IGNORE" columns get ignored during mapping in the deserializer, and I end up getting "Nickname" values for "DOB", resulting in invalid values for the DOB field.

Answer 1

My mistake was defining the schema as follows, which apparently strongly couples the schema to the domain POJO:

CsvSchema schema = mapper
    .typedSchemaFor(Person.class)
    .withSkipFirstDataRow(hasHeader)
    .sortedBy(columnOrder.toArray(new String[columnOrder.size()]));

Resolved by defining schema/columns as follows, which seems to loosly couple the schema to the domain POJO:

CsvSchema schema = CsvSchema.builder()
    .addColumn("firstName")
    .addColumn("lastName")
    .addColumn("ignore1")
    .addColumn("dob")
    .addColumn("ignore2")
    .addColumn("postalCode")
    .build();

    CsvMapper mapper = new CsvMapper();
    MappingIterator<Person> personIter = mapper
            .readerFor(Person.class)
            .with(schema)
            .readValues(csvFile);

Answer 2

Ignoring unknown can be achieved as shown below(tested using jackson 2.13):

1. Annotate POJO

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import java.time.LocalDate;

@JsonIgnoreProperties(ignoreUnknown = true) //this is the trick to ignore all undeclared columns
public class Person {
    @JsonProperty("First Name") //declare what's needed
    private String firstName;
    private String lastName;
    private LocalDate dob;
    private String postalCode;
}

2. Configure csvSchema

CsvMapper csvMapper = new CsvMapper();
CsvSchema csvSchema = csvMapper
    .schemaFor(Person.class)
    .withHeader()//header defines the order
    .withColumnReordering(true)//this allows columns to be in any order as long as there is a header
    ;

3. Finally, use it to read csv file

csvMapper.readerFor(Person.class).with(csvSchema).readValues(csvFile)