You can't convert an input stream to an output stream. That's like
asking how to convert a fountain to a wet-vac.

InputStream is used to read data from, and an OutputStream is where
you send data to.  What exactly are you trying to do?

If you have a thread that is writing to an OutputStream and you want to
read the results from an InputStream, either use Piped(In|Out)putStream,
or buffer the whole thing in a BufferedArrayOutputStream and then use
toByteArray followed by a new BufferedArrayInputStream.

If you have a method of some description that requires an InputStream
and you want to feed it through an OutputStream, either create a thread
that copies from input to output, or do the same thing as above with
BufferedArray(In|Out)putStream.

Tom Hawtin