I was trying to follow some instructions today, and it starts with the comment
REM In SQLPlus I manually copy in each line and execute it.
I was looking through the help files and found how to do it in SQL Developer Concepts and Usage->Using the SQL Worksheet->Script Runner.
Basically, you have to precede the file name with an @. For example @C:\MyScript\Script.sql.
You can then run a batch of them this way. Note that the command doesn't seem to like spaces in the file path.