JDBC Blob helper class & streaming uploaded data into PG

Does anybody have a JDBC Blob helper class so we can use the
setBlob()/getBlob() calls in JDBC for PG 8.3? It would be a class that
implements the java.sql.Blob interface.

Does anybody have any code samples of how I'd go about reading a file in
blocks, compressing the block and then streaming that block into a Blob
(LO)? We are starting to process very large files uploaded in a web app
and so it's no longer possible to keep it all in memory before it's
stored in PG.

The pseudo-code is something like:

while ( hasMoreHttpPostData )
{
read chunk from HTTP POST
compress chunk
write chunk to DB
}

If possible, we'd like to use a streaming cipher (for encryption) and
GZIP to write the compressed data and a Blob to store to the database.

Do these APIs support writing chunks, or must we actually loop through
each byte (which seems painfully slow).

Thanks,
David