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]}]
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