You could do this:
InputStream in = new ByteArrayInputStream(string.getBytes("UTF-8"));
Note the UTF-8 encoding. You should specify the character set that you want the bytes encoded into. It's common to choose UTF-8 if you don't specifically need anything else. Otherwise if you select nothing you'll get the default encoding that can vary between systems. From the JavaDoc:
The behavior of this method when this string cannot be encoded in the default charset is unspecified. The CharsetEncoder class should be used when more control over the encoding process is required.