Reverse Proxy: URL paths are incorrectly encoded

When using the reverse proxy, url paths are encoded using the wrong type of encoding. It is using the awfully named java.net.URLEncoder which cannot be used to encode paths within a url.

https://github.com/undertow-io/undertow/blob/master/core/src/main/java/io/undertow/server/handlers/proxy/ProxyHandler.java#L704

What is happening is a proper url such as http://localhost:8080/foo%20bar gets sent across as http://localhost:8080/foo+bar which is incorrect.

An excellent blog post on the different types of url encoding can be found here http://blog.lunatech.com/2009/02/03/what-every-web-developer-must-know-about-url-encoding
[the only thing that post doesn't tell you is how to property encode paths in java, but I believe its as simple as something like new URI(null, null, myPath, null).getRawPath()]