Reads body-data
from the current encapsulation
and writes its contents into the output Stream
.
Arbitrary large amounts of data can be processed by this method using a constant size buffer. (see {@link #MultipartStream(InputStream,byte[],int,MultipartStream.ProgressNotifier) constructor}).
@param output The Stream
to write data into. Maybe null, in which case this method is equivalent to {@link #discardBodyData()}.
@return the amount of data written.
@throws MalformedStreamException if the stream ends unexpectedly.
@throws IOException if an i/o error occurs.