Records and Jackson

Jackson is a popular library to serialize Java objects to JSON, and since version 2.12 it also supports records!
Let's see how we can use it.

Reading or writing a record

Records are supported out of the box since Jackson 2.12, and work just as their equivalent POJO

record Customer(UUID id, String firstName) {}

can be read from or written as

{
  "id": "7fe05925-18d8-4284-a15c-8af6f33f1d6e",
  "firstName": "John"
}

All normal Jackson options and configuration will be respected.

Annotations like JsonAlias, JsonValue or

Known bugs

Unfortunately, the latest Jackson version at the time of writing - 2.13.4 - has done known bugs or unsupported situations with records. Here I list them and provide work-arounds

Scalar values with @JsonValue

Records provide a natural way to wrap a scalar value, introducing a custom type that serializes to the underlying JSON type.

For example, we might want to restrict valid JSON inputs to positive numbers:

record PositiveInt(@JsonValue int value) {
  @JsonCreator
  PositiveInt {
    if(value <= 0) {
      throw new IllegalArgumentException("value " + value + " must be positive");
    }
  }
}

Unfortunately, due to

TODO: describe BUG

Leaving out components

Adding additional data to serialized JSON

Default values

Validation

Normalization