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XML

Artifact: problem-details-xml. Media type: application/problem+xml. Nothing extra to install — reading and writing use the XML support already in the JDK.

String xml = ProblemXml.toXml(problem);
ProblemDetail readBack = ProblemXml.fromXml(xml);

(Streaming variants taking XMLStreamWriter/XMLStreamReader exist for pipelines. Everything reports failures as the checked XMLStreamException — one exception type for all of it.)

What the XML looks like

One child element per field, extensions after the standard ones:

<?xml version="1.0" encoding="UTF-8"?>
<problem xmlns="urn:ietf:rfc:7807">
  <type>https://example.com/probs/out-of-credit</type>
  <title>You do not have enough credit.</title>
  <detail>Your current balance is 30, but that costs 50.</detail>
  <instance>https://example.net/account/12345/msgs/abc</instance>
  <balance>30</balance>
  <accounts>
    <i>https://example.net/account/12345</i>
    <i>https://example.net/account/67890</i>
  </accounts>
</problem>

Two things to know, both inherited from the format itself rather than this library: an element with children is an object, except one whose children are all named i — that's an array. And yes, the namespace really says 7807: the RFC kept it from the older spec it replaced.

Only String, numbers, booleans, lists, and maps can be written — anything else fails fast with a clear error instead of silent garbage. The same goes for field names that aren't valid XML.

Two quirks worth knowing upfront

  1. Numbers come back as strings. XML carries no types, so <balance>30</balance> reads back as "30". Nothing is guessed — which is also what keeps values like "01234" intact. If typed round-trips matter to you, use JSON.
  2. Empty lists and maps have no representation. They write as an empty element and read back as an empty string.

Otherwise reading is as forgiving as the JSON side: bad URIs, bad statuses, and markup where text belongs are skipped; unknown elements become extensions; stray whitespace is trimmed. And hostile input (entity bombs and the like) is rejected — DTDs and external entities stay off.