Jackson JSON parsing top-level map into records

Java 14 added the record type and Jackson JSON works great with them.

I hit an edge case where I needed to parse a JSON structure where the top level was an object with arbitrary keys.

I also didn't want to read into a Map but rather a record that mapped each keyed entry into a record each.

Here's a contrived example JSON I wanted to parse:

{ "Some Child's Name": { "age": 5 }, "Some Adult's Name": { "age": 21 } } 

The @JsonAnySetter annotation (1) on a Map field got me most of the way, but the final piece of the solution was to pre-instantiate the map at (2).

Here are the final record declarations that can accommodate the JSON above:

record People( @JsonAnySetter // (1) Map<String, Person> people ) { public People { people = new HashMap<>(); // (2) } } record Person( int age ) { } 

For example, following use of an ObjectMapper ...

final People people = objectMapper.readValue(""" { "Some Child's Name": { "age": 5 }, "Some Adult's Name": { "age": 21 } }""", People.class); System.out.println(people); 

outputs

People[people={Some Adult's Name=Person[age=21], Some Child's Name=Person[age=5]}]