the new project specification states that:
You must not use parts of the Java standard library that parse URIs/URLs, neither direct nor indirect. In particular, using the java.net library is not allowed for this project.
java.util.regex.Pattern (link) allowed?
Also there is no URI category yet for the forum.
Indeed, that is allowed. Some tutors even would encourage it.
Would (in theory) writing one huge regex pattern that does the whole parsing for us be valid?
Yes. Good luck! You will need it.
That would be a nightmare to maintain, but you probably know that
Also while in this case it might be possible it is in general not possible to parse arbitrary grammars just using regular expressions (or even regex).
java.util.regex and subpackages are allowed.