A transparent stream that updates the associated message digest using
the bits going through the stream.
To complete the message digest computation, call one of the
digest methods on the associated message
digest after your calls to one of this digest input stream's read methods.
It is possible to turn this stream on or off (see on). When it is on, a call to read
results in an update on the message digest. But when it is off,
the message digest is not updated. The default is for the stream
to be on.
Note that digest objects can compute only one digest (see MessageDigest),
so that in order to compute intermediate digests, a caller should
retain a handle onto the digest object, and clone it for each
digest to be computed, leaving the orginal digest untouched.
Reads a byte, and updates the message digest (if the digest
function is on). That is, this method reads a byte from the
input stream, blocking until the byte is actually read. If the
digest function is on (see on), this method
will then call update on the message digest associated
with this stream, passing it the byte read.
Reads into a byte array, and updates the message digest (if the
digest function is on). That is, this method reads up to
len bytes from the input stream into the array
b, starting at offset off. This method
blocks until the data is actually
read. If the digest function is on (see on), this method will then call update
on the message digest associated with this stream, passing it
b - the array into which the data is read.
off - the starting offset into b of where the
data should be placed.
len - the maximum number of bytes to be read from the input
stream into b, starting at offset off.
the actual number of bytes read. This is less than
len if the end of the stream is reached prior to
reading len bytes. -1 is returned if no bytes were
read because the end of the stream had already been reached when
the call was made.