JSON

Artifact: problem-details-jackson. Media type: application/problem+json. Needs Jackson 3.

Setup

Add the artifact next to problem-details-core (same group ID, same version), then register the module once:

JsonMapper mapper = JsonMapper.builder()
    .addModule(new ProblemDetailsModule())
    .build();

That one registration is what teaches Jackson the format — without it you get an ordinary bean dump.

Writing

Fields come out in the RFC's order, missing fields are simply left out, and your custom fields follow in the order you added them. (type is always there — the core fills in about:blank for you.)

{
  "type": "https://example.com/probs/out-of-credit",
  "title": "You do not have enough credit.",
  "detail": "Your current balance is 30, but that costs 50.",
  "instance": "/account/12345/msgs/abc",
  "balance": 30,
  "accounts": ["/account/12345", "/account/67890"]
}

Custom values can be strings, numbers, booleans, lists, or maps, nested as deeply as you like.

Reading

ProblemDetail problem = mapper.readValue(json, ProblemDetail.class);

Reading forgives a lot, by design: a field with the wrong type is skipped as if it weren't there, JSON nulls count as absent, and an out-of-range status is dropped. Unknown fields are never lost — they become extensions, so an older reader still round-trips a newer producer's output without damage.

Values land in natural Java types (strings stay strings, whole numbers become Integer or Long, decimals become Double, arrays become lists, objects become maps), and you read them back through your own keys:

problem.get(ProblemDetailKey.of("balance", Integer.class)) // Optional[30]