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Registry

Artifact: problem-details-registry. Before inventing an error type, check whether a reusable one already exists — that's what this module is for.

Look one up

ProblemTypeRegistry registry = new ProblemTypeRegistry(); // starts with about:blank
Optional<ProblemType> known = registry.lookup("https://example.com/probs/out-of-credit");

For the built-in ones there's an even shorter path:

ProblemTypes.lookup("about:blank");

Add your own

Nothing suitable? Mint a stable URI under your own control, give it a title and a status, point at your docs — and register it so the rest of your code finds it in one place:

registry.register(
    ProblemType.of("https://example.com/probs/out-of-credit",
        "You do not have enough credit.", 403, "https://example.com/docs/probs"));

Each entry holds the type URI, a short title, the recommended status (empty when there is none, like about:blank), and a reference to wherever it's documented.

Three things the registry guarantees so you can share it across your app:

  • Typos can't shadow entries. Registering an already-known URI fails loudly instead of quietly replacing something — possibly someone else's standard type.
  • Registries don't leak into each other. Each instance is independent, and the shared ProblemTypes lookup is read-only.
  • Threads are fine. Lookups and registrations can race safely.

One subtlety about about:blank: its registered title, "See HTTP Status Code", is an instruction, not a title. When you use that type, set the title to your response's status phrase (Not Found for a 404, in the client's language if you like) — that's what the RFC asks for.