Long story short, I need to convert a dll to be a Java class file so it will be portable. Is this feasible?

I had the idea of taking a C# compiler written in C# and turning it to be a C# compiler written in Java, so it'd be portable. The C# compiler is opensource, so I can hack around with it as much as I'd like

Or would it be easier to take the .csc files and convert them to be .java files? Or simply go line-by-line and re-write it all?