Use java.io.StringReader: return new StringReader(string);.
Next time you need a reader, you can check the “Direct known subclasses” of the Reader class. Same goes for InputStream, etc. The place to start is the javadoc – it contains quite a lot of useful information.
But for your task at hand, you’d better follow Jon Lin’ advice of simply using a FileReader. There is no need to go through String. (For that, my advice from the previous paragraph applies as well)