@Override
    public Object readFrom(
            Class<Object> type,
            Type genericType,
            Annotation[] annotations,
            MediaType mediaType,
            MultivaluedMap<String, String> httpHeaders,
            InputStream entityStream
    ) throws IOException, WebApplicationException {
        try {
            FastJsonConfig fastJsonConfig = locateConfigProvider(type, mediaType);

            return JSON.parseObject(entityStream,
                    fastJsonConfig.getCharset(),
                    genericType,
                    fastJsonConfig.getParserConfig(),
                    fastJsonConfig.getParseProcess(),
                    JSON.DEFAULT_PARSER_FEATURE,
                    fastJsonConfig.getFeatures());
        } catch (JSONException ex) {
            throw new WebApplicationException(ex);
        }
    }
Method that JAX-RS container calls to deserialize given value.
fastjson1-compatible/src/main/java/com/alibaba/fastjson/support/jaxrs/FastJsonProvider.java