How to alias prefixed CSV columns to a Map with SimpleFlatMapper?

Question

Background

Using SimpleFlatMapper sfm-csv 6.0.3

Example CSV:

|------|-------------|----------------|----------------|------------------|
| name | reference # | pf.first thing | pf.secondThing | pf.another.thing |
|======|=============|================|================|==================|
| foo  | eb2e23c0d6a | a value here   |                | another value    |
|------|-------------|----------------|----------------|------------------|
| bar  | 0a4bba4c1d0 | values         | all            | throughout       |
|------|-------------|----------------|----------------|------------------|

Pojo

class Item {

    private String name;
    private String reference;
    private Map<String, String> prefixedFields;

    // ... builder, getters, etc.

}

Simplified code

final CsvMapper<Item> mapper = CsvMapperFactory.newInstance()
    .addAlias("name", "itemName")
    .addAlias("reference #", "reference")
    .newMapper(Item.class);

return CsvParser.mapWith(mapper)
    .stream(file, items -> items.collect(List.collector()));

Problem

As is, the Map is coming back null. I'm trying to get to a point where:

firstRowItem.getPrefixedFields() == ImmutableMap.of(
    "first thing", "a value here",
    "another.thing", "another value")

secondRowItem.getPrefixedFields() == ImmutableMap.of(
    "first thing", "values",
    "secondThing", "all",
    "another.thing", "throughout")

The "pf." prefix is set in stone, and everything works if the property is named "pf":

class Item {
    // ...
    private Map<String, String> pf;
    // ...
}

but I'd like for the property to be named "prefixedFields" instead of "pf".

Attempts at resolution

The SimpleFlatMapper docs on property mapping shows how to match the "pf." prefix, but doesn't cover aliasing a Map:

.addColumnProperty(
    col -> col.getName().startsWith("pf."),
    MapTypeProperty.KEY_VALUE)

.addAlias only accepts String params, so something like this doesn't work:

.addAlias("pf.", "prefixedFields")

score 1 · Accepted Answer · answered Apr 05 '19 at 18:42

A comment on a GitHub issue from the project owner got me on the right track.

addColumnProperty accepts varargs of Object. You can pass in a RenameProperty, which accepts either a String param for simple column renaming or a Function<String, String> renameFunction. Put those together like so:

final CsvMapper<Item> mapper = CsvMapperFactory.newInstance()
    .addAlias("name", "itemName")
    .addAlias("reference #", "reference")
    .addColumnProperty(
        column -> column.getName().startsWith("pf."),
        new RenameProperty(columnName -> columnName.replace("pf.", "prefixedFields_")))
    .newMapper(Item.class);