I’m attempting to make a POST request to a FastApi from a Java front-end. I have tried several different things I have found reading online, but I cannot make it work.

Java implementation:

    public JSONObject saveData(JSONObject data) {
    JSONObject jsonResponse;
    try {
        HttpClient client = newHttpClient();

        HttpRequest request = HttpRequest.newBuilder(URI.create(apiUrl + "save_variants"))
                .version(HttpClient.Version.HTTP_2)
                .header("accept", "application/json")
                .POST(HttpRequest.BodyPublishers.ofString(data.toString()))
                .build();

        HttpResponse<String> response =
                client.send(request, HttpResponse.BodyHandlers.ofString());

        String jsonString = response.body().replaceAll("\\","");
        jsonResponse = new JSONObject(jsonString);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }

    System.out.println("Received updated data:" + jsonResponse);

    return jsonResponse;
}

Python FastApi post:

class Item(BaseModel):
    item: str


@app.post("/variants")
async def save_variants(item: Item):
    logger.info(f"Payload:${item}")

    return read_param_json("variant_parameters_original.json")

On FastApi side:

I can’t seem to get the correct data passed to FastApi, or get FastApi to read it correctly – unsure where the problem is exactly.

I tried this: How to make a JSON POST request from Java client to Python FastAPI server?, same error