Why does Java automatically decode / in URI encoded filenames?

Question

I have a servlet that needs to write out files that have a user-configurable name. I am trying to use URI encoding to properly escape special characters, but the JRE appear

Answer 1

The new File(URI) constructs the file based on the path as obtained by URI#getPath() instead of -what you expected- URI#getRawPath(). This look like a feature "by design".

You have 2 options:

1. Run URLEncoder#encode() on fn twice (note: encode(), not encoder()).
2. Use new File(String) instead.