quarkusio/quarkus · error · IllegalArgumentException

Unknown JSON Value {kind}

Error message

Unknown JSON Value {kind}

What it means

VertxJson converts jakarta.json values into Vert.x JsonObject/JsonArray by recursively copying entries. Its copy switch handles NULL, TRUE, FALSE, STRING, NUMBER, and OBJECT kinds; if a jakarta.json value has another kind (i.e. ARRAY appearing in the object-entry copy path, or any future/unexpected kind), it throws IllegalArgumentException "Unknown JSON Value <kind>". This indicates a conversion gap, typically when a jakarta.json array is nested inside a JsonObject being converted to a Vert.x JsonObject.

Source

Thrown at extensions/resteasy-reactive/rest-jsonb-common/runtime/src/main/java/io/quarkus/resteasy/reactive/jsonb/common/runtime/serialisers/VertxJson.java:66

                    JsonNumber number = origin.getJsonNumber(key);
                    if (number.isIntegral()) {
                        object.put(key, number.longValue());
                    } else {
                        object.put(key, number.doubleValue());
                    }
                    break;
                case ARRAY:
                    JsonArray array = new JsonArray();
                    copy(array, origin.getJsonArray(key));
                    object.put(key, array);
                    break;
                case OBJECT:
                    JsonObject json = new JsonObject();
                    copy(json, origin.getJsonObject(key));
                    object.put(key, json);
                    break;
                default:
                    throw new IllegalArgumentException("Unknown JSON Value " + kind);
            }
        });
    }

    public static void copy(JsonArray array, jakarta.json.JsonArray origin) {
        for (int i = 0; i < origin.size(); i++) {
            JsonValue value = origin.get(i);
            JsonValue.ValueType kind = value.getValueType();
            switch (kind) {
                case STRING:
                    array.add(origin.getString(i));
                    break;
                case TRUE:
                    array.add(true);
                    break;
                case FALSE:
                    array.add(false);
                    break;

View on GitHub (pinned to e1c734241f)

Solutions

1. Avoid nesting jakarta.json.JsonArray inside a jakarta.json JsonObject passed to VertxJson; build the structure directly as Vert.x JsonObject/JsonArray
2. Convert with jakarta.json's own toString()/reader and parse into Vert.x types (new JsonObject(jsonString)) instead of using VertxJson.copy
3. Upgrade Quarkus — check if a fixed version handles ARRAY in this copy path; if not, file a bug with a reproducer
4. Flatten the payload so object entries are only scalars, nulls, booleans, or nested objects before conversion

Example fix

// before
JsonObject origin = Json.createObjectBuilder().add("tags", Json.createArrayBuilder().add("a")).build();
VertxJson.copy(vertxObject, origin); // throws: Unknown JSON Value ARRAY

// after
io.vertx.core.json.JsonObject v = new io.vertx.core.json.JsonObject(origin.toString());

static void assertNoNestedArrays(jakarta.json.JsonObject o) {
    for (String k : o.keySet()) {
        if (o.get(k) instanceof jakarta.json.JsonArray)
            throw new IllegalArgumentException("Nested jakarta.json arrays are unsupported by VertxJson.copy: " + k);
    }
}

static boolean isVertxCopySafe(jakarta.json.JsonValue v) {
    if (v instanceof jakarta.json.JsonObject o)
        return o.values().stream().noneMatch(x -> x instanceof jakarta.json.JsonArray);
    return !(v instanceof jakarta.json.JsonArray);
}

try {
    VertxJson.copy(target, origin);
} catch (IllegalArgumentException e) {
    if (e.getMessage() != null && e.getMessage().startsWith("Unknown JSON Value")) {
        io.vertx.core.json.JsonObject fallback = new io.vertx.core.json.JsonObject(origin.toString());
    }
}

When it happens

Trigger: Calling the VertxJson serializer/converter on a jakarta.json JsonObject that contains a nested jakarta.json.JsonArray value (the object-copy switch lacks an ARRAY case), producing the error at runtime during request body reading/writing.

Common situations: Using jakarta.json (Json-P) structures with JSON-B/RESTEasy Reactive JSON-B endpoints where nested arrays exist inside objects; differences between Json-P and Vert.x JSON APIs when bridging both JSON stacks in one app; building payloads with Json.createObjectBuilder().add("list", arrayBuilder).

Related errors

• Unknown JSON Value ${kind}
• Cannot create JsonArray
• Cannot create JsonObject
• Unknown JSON Value
• Failed to encode as JSON:

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/b7786921f39c56e6. Report an issue: GitHub.