The UriBuilder spec says: Builder methods perform contextual encoding of characters not permitted in the corresponding URI component following the rules of the application/x-www-form-urlencoded media type for query parameters.

Both "" and "%20" are permitted in query parameter values but RESTEasy 1.1.GA encodes "" and skips "%20".

In fact, I don't see the value of contextual encoding for query parameters. In most cases I have parameter values containing any characters like "%", "+", or "{", so I always encode them manually before passing to UriBuilder.queryParam.

An alternative way is to use templates when a build with RESTEASY-266 fixed is released, but this approach is also quite inconvenient when building URLs with many optional parameters.