writing to a file chunk by chunk

manolakis · 10-24-2014, 01:06 PM

Dear all,

I basically have a TCP client\server where the server sends a big file to the client chunk by chunk. I basically want to ask how is it possible to write to an output file a byte array each time a chunk is received.
An example can be:

Quote:

public class Chunk implements Serializable
{
private byte [] data;
// getters and setters
}

public class Client extends Thread
{

public void run()
{
Chunk chunk = (Chunk) readMessage();
}
}

Thank you.

NevemTeve · 10-24-2014, 01:50 PM

http://docs.oracle.com/javase/7/docs...putStream.html

manolakis · 10-24-2014, 02:01 PM

NevemTeve,

Thanks for your reply. I do not really know on how much I can use a FileOutputStream to write to the file. For instance, I might receive chunks in a random order. I had a thought about FileOutputStream but I am not 100% sure if write(byte[], int, int) will necessarily work. Do you believe that write(byte[], int, int) will necessarily work?

Thank you.

metaschima · 10-24-2014, 02:25 PM

You could create a file full of zeros for the full file size and then write the chunks in the right place as you receive them.

I guess you could also just buffer them, but with large files this will not work.

NevemTeve · 10-25-2014, 12:10 AM

> For instance, I might receive chunks in a random order.

With TCP? How would it be possible? Perhaps you thought of UDP?

manolakis · 10-25-2014, 03:38 AM

NevemTeve,

Once more again thanks for your interest. I would really like to ask you that because I do not have so much experience with TCP sockets programming. Setting the case that a TCP client\server will communicate with the use of Object Messages rather than sending data through a byte stream what I would like to know if there is message delivery guarantee, and if there is any need for acknoledging Object Messages. Therefore, is every message guaranteed to be received. Will Java retransmit itself corrupted messages?

Sincerely,
Emmanouil.

NevemTeve · 10-25-2014, 05:51 AM

I don't know what 'Object Messages' are, but I can tell you what TCP is: full-duplex reliable bytestream between two parties (actually, it is two independent bytestreams). The bytes arrive in the order they were sent (no loss, no duplication, no reorder), but message boundaries aren't reserved.

manolakis · 10-25-2014, 06:32 AM

NevemTeve,

So if i try to send a message of 32Kb, which might be quiet large, does TCP quarantees that the message will be delivered correctly?

NevemTeve · 10-25-2014, 06:57 AM

Actually, there's no messages, only byte-streams: the remote side will receive every byte in the same order you sent them, but not neccessarily in one part: it might first receive one byte, then 30000 bytes, then 767 bytes... (Of course, the connection still might get lost during the transfer.)

manolakis · 10-25-2014, 07:26 AM

I actually used the FileOutputStream that you told me and I can successfully send and write to disk some files. The only that really bothers me is if I try to write a bad chunk (a message altered due to communication problems) to the FileOutputStream I do not really believe that I can overwrite the chunk. The FileOutputStream I think only supports continuous writes of bytes. Do you really know any possible way to specify a method like

Quote:

write(byte [] data, int streamStartOffset)

This should actually write the data starting at specified streamStartOffset. So if I have a file of 1024 bytes, write(data, 0) will indicate that the data will be written starting from index 0.

Really thanks.

NevemTeve · 10-25-2014, 07:40 AM

> write a bad chunk (a message altered due to communication problems)

With TCP? How would it be possible?

Nontheless, there is RandomAccessFile in Java: http://docs.oracle.com/javase/7/docs...ccessFile.html