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How can I compress my data to save bandwidth when sending across a socket?
Location: http://www.jguru.com/faq/view.jsp?EID=3823
Created: Dec 31, 1999 Modified: 2002-03-25 09:34:57.661
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)
The GZIPInputStream and GZIPOutputStream classes found in the java.util.zip package
compress data with the GZIP file format, as defined by RFC 1952
(ftp://ftp.uu.net/graphics/png/documents/zlib/zdoc-index.html).
See also http://cnrit.tamu.edu/sir_anodos/ for classes to use compression over a
network stream. [User seems to have left university. Anyone know where it went?]
Comments and alternative answers
For more info, see How can I compress/uncompress a...
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7), Oct 1, 2000
For more info, see How can I compress/uncompress a long string or a file (of any
type)?.
Doesn't work so well with live Socket communications.
Author: Andy DePue (http://www.jguru.com/guru/viewbio.jsp?EID=24220), Mar 28, 2001
The short answer above doesn't really help those people who want to add a
compression layer to their socket streams. The reality is, if you wrap your Socket
streams in these compressed streams, you will find that your client or server will
seem to hang. Why? Say you write a byte to a GZip stream... does that mean a byte (or
less than a byte) comes out on the other end right when you write it? Nope. The GZip
streams do not write to the underlying stream until there are enough bytes on the
incoming side to send compressed bytes to the outgoing side. Here is an example:
Client A connects to Server B. They both use the GZip streams to compress their
socket streams. Server B sends a HELLO message to Client A, but Client A never
receives it because the GZip output stream on Server B doesn't have enough data to
compress to output anything. Meanwhile, Server B is waiting for an ACK from Client A,
and never gets it because Client A never got its HELLO message. Nothing else happens.
Again, this is because Server B never sent all the HELLO bytes out of its Socket to
Client A, because the GZip streams hold on to the outgoing data until they have
enough to compress. And calling flush() doesn't help at all. An alternative is not to
wrap the Socket streams in the GZIP streams, but instead individually compress the
pieces you send (in other words, put a GZIP output stream around a
ByteArrayOutputStream, write out your data, close the stream, and then send the
resulting byte array from the ByteArrayOutputStream out the socket). This, of course,
is not very effecient CPU, memory, or compression wise. Anyone else have any ideas on
how to wrap a Socket stream in a GZIP stream and have it actually work?
Re: Doesn't work so well with live Socket communications.
Author: Mark Phillips (http://www.jguru.com/guru/viewbio.jsp?EID=134288), Jul 12, 2002
About a year ago I wrestled with the same problem Andy outlines and failed to solve it.
Nowadays I expect the task is fairly easily accomplished with NIO and ByteBuffers.
You compress your data before loading it into your ByteBuffer for transmission.
Steams be damned, LOL.
--Mark
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Fernando Henrique da Silva wrote:
Olá amigos! Tudo bem?
Estou utilizando uma estrutura cliente-servidor, e estou utilizando
strings para o diálogo entre o cliente e o servidor. Abaixo disso
utilizo a classe GZIPOutputStream e a GZIPInputStream. Ou seja:
GZIPOutputStream gzipout = new
GZIPOutputStream(socket.getOutputStream());
PrintWriter out = new PrintWriter( gzipout );
Teoricamente, após eu escrever a mensagem de um para o outro, eu
devo utilizar a função finish() para finalizar a escrita.
Segundo a documentação, a função finish Finishes writing compressed
data to the output stream without closing the underlying stream e
dispara exceções.
O problema é que sempre ela dispara exceções, e depois disso eu não
consigo mais nem enviar nem receber strings pelos sockets, embora a
conexão não caia.
O que está acontecendo?
Se possível, enviar a resposta também para o email
[EMAIL PROTECTED] mailto:[EMAIL PROTECTED]
Obrigado desde já!
Rael Gugelmin Cunha
graduando
em c.computação
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