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.
src/main/java/com/alibaba/fastjson/support/jaxrs/FastJsonProvider.java