HMCL-dev/HMCL · error · JsonParseException

json.toString()

Error message

json.toString()

What it means

The Gson deserializer for JavaLocalFiles.Local requires the JSON element to be an object; a JsonParseException wrapping json.toString() is thrown when the element is an array, string, number, boolean, or null. This is a shape guard before reading the polymorphic `type` discriminator. It indicates corrupt or malformed data in a file describing a local Java installation entry.

Solutions

1. Open the JSON file and fix the malformed entry so it is an object with a `type` field ("file", "directory", or "link").
2. Restore the file from backup or delete it so the library regenerates defaults.
3. Validate the whole file with a JSON linter/schema check before loading it in the app.
4. If generating such files programmatically, always serialize through JavaLocalFiles.Serializer rather than writing raw JSON.

Example fix

// before
"java": "path/to/jdk"
// after
"java": { "type": "file", "sha1": "...", "size": 12345 }

JsonElement el = JsonParser.parseString(raw);
if (!el.isJsonObject()) {
    throw new IllegalArgumentException("entry must be a JSON object, got: " + el);
}

try {
    Local local = gson.fromJson(raw, JavaLocalFiles.Local.class);
} catch (JsonParseException e) {
    LOG.warning("Malformed local-java entry (must be an object with type): " + e.getMessage());
    // skip entry or restore from backup
}

When it happens

Trigger: Gson deserializing a JSON value that is not an object (e.g. a bare string, array, or null literal) into type JavaLocalFiles.Local via the Serializer.deserialize adapter.

Common situations: A hand-edited or corrupted java-related JSON file (java repositories / custom runtime lists) where an entry was replaced by a scalar or array; an older schema version that stored entries differently; a truncation or merge conflict that broke the JSON structure.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Config is not an object:
• Protected payload is not a
• Expected JsonObject but got
• PortablePath must be a string: " + in.peek()
• this.getClass() + " cannot be deserialized to " + type

AI-assisted analysis of HMCL-dev/HMCL@24702dc5a0 (2026-09-10). Data as JSON: /api/errors/b0696511cd9bb954. Report an issue: GitHub.

Appendix: source

Thrown at HMCL/src/main/java/org/jackhuang/hmcl/java/JavaLocalFiles.java:98

    public static class Serializer implements JsonSerializer<Local>, JsonDeserializer<Local> {

        @Override
        public JsonElement serialize(Local src, Type typeOfSrc, JsonSerializationContext context) {
            JsonObject obj = new JsonObject();
            obj.addProperty("type", src.getType());
            if (src instanceof LocalFile) {
                obj.addProperty("sha1", ((LocalFile) src).getSha1());
                obj.addProperty("size", ((LocalFile) src).getSize());
            } else if (src instanceof LocalLink) {
                obj.addProperty("target", ((LocalLink) src).getTarget());
            }
            return obj;
        }

        @Override
        public Local deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
            if (!json.isJsonObject())
                throw new JsonParseException(json.toString());

            JsonObject obj = json.getAsJsonObject();
            if (!obj.has("type"))
                throw new JsonParseException(json.toString());

            String type = obj.getAsJsonPrimitive("type").getAsString();

            try {
                switch (type) {
                    case "file": {
                        String sha1 = obj.getAsJsonPrimitive("sha1").getAsString();
                        long size = obj.getAsJsonPrimitive("size").getAsLong();
                        return new LocalFile(sha1, size);
                    }
                    case "directory": {
                        return new LocalDirectory();
                    }
                    case "link": {

View on GitHub (pinned to 24702dc5a0)