How to lose time with something you can't see...

While working I encounter a strange exception:

java.net.URISyntaxException: Illegal character in query at index 79: http:// ...

Strange, because there was no special character in my URL. The index 79 was here:

&v4003=
  ^

I couldn't figure out what the problem was... Then I decided to try something out:

System.out.println(URLEncoder.encode("v4003=", "UTF-8"));

And the output was

v%E2%80%8B4003%3D

So, what is this %E2%80%8B? After so many years I learned for the first time that this is the zero width space character. A very devious character, really!

So, how did this character came in my URL? It was a result of (of course) a copy paste from the google docs. I was too lazy to write 4000 with the keyboard. And laziness is something that always creates strange problems.