@Override
    public Object readFrom(
            Class<Object> type,
            Type genericType,
            Annotation[] annotations,
            MediaType mediaType,
            MultivaluedMap<String, String> httpHeaders,
            InputStream entityStream
    ) throws IOException, WebApplicationException {
        FastJsonConfig config = locateConfigProvider(type, mediaType);
        try (ByteArrayOutputStream baos = new ByteArrayOutputStream()) {
            byte[] buf = new byte[1024 * 64];
            for (; ; ) {
                int len = entityStream.read(buf);
                if (len == -1) {
                    break;
                }
                if (len > 0) {
                    baos.write(buf, 0, len);
                }
            }
            byte[] bytes = baos.toByteArray();
            return JSON.parseObject(bytes, genericType, config.getDateFormat(), config.getReaderFilters(), config.getReaderFeatures());
        } catch (JSONException ex) {
            throw new WebApplicationException(ex);
        }
    }
Method that JAX-RS container calls to deserialize given value.
extension-jaxrs/extension-jaxrs-jakarta/src/main/java/com/alibaba/fastjson2/support/jaxrs/jakarta/FastJson2Provider.java