Java Networking help to understand sockets

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14 comments, last by Canvas 11 years, 2 months ago
Multicast does not work over the Internet, just an FYI.
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ah ok :) maybe why I can't get any information about it, well here is a quick question, Looking at this link here http://docs.oracle.com/javase/tutorial/networking/sockets/clientServer.html it has the code for a server that will commuicate with a user and an upgraded version to handle multiple users, I have ran the code and commented it and at last I'm finaling starting to understand it, but just one little tiny bit I'm still a little confused with, the client and server both have input and output streams of some sort, the server has hold of the clients what? output stream or input stream? and what does the client have a hold of on the server? the servers output stream or input stream? I just can't figure out which stream is used for what :), they seem quite equal.

My Java is very rusty. I would assume that the client has an output stream that writes to a socket. The server will then have another, connected, socket, which it reads from using an input stream. To return data (over TCP sockets,) the server would then have an output stream connected to the same server-side socket. Finally, data that the server writes ends up received on the client socket, and read from that socket by the client through an InputStream.
enum Bool { True, False, FileNotFound };

the server has hold of the clients what? output stream or input stream? and what does the client have a hold of on the server? the servers output stream or input stream?

Don't get confused here. The Java Server Socket library is a wrapper for using TCP/IP networking communication. Any socket, whether a client or server socket, has both an input stream and an output stream. It reads data "in" from the input stream and writes data "out" to the output stream. But the server or client doesn't hold a stream from the other code. You can write a client that talks to a Google server and gets the home page. You have no idea what language or operating system Google is using, and that's the point. The TCP/IP protocol handles all that crap for you so you can just write code. And all the (really) low level code is wrapped up in the ServerSocket library.

If you write data to an output stream, then the server would need to read from the output stream if is held a reference to the same stream. But it doesn't work that way, because that would get really difficult. It is client output the input? This stuff's hard enough without something like that to worry about.

Start you server, and accept() a connection, which will block waiting for someone to connect.
Start your client, and try to connect to the server.
The server's accept() will return, and allow the client to connect.
Now the server reads some data. Since there is no data to read (because the client hasn't sent anything) it will block.

Then the client will be connected, and can send data. After sending data, the client will attempt to read() the response, which will block.
The Server will get the request, do something with it, and return a response. The server then tries to read some more data().

The client then reads the response. And so one. I suggest trying to get a simple client that connects to www.google.com and pulls some data before trying to write the server too. Once you know you've got the client working, if it is broke, it's the server.

Have Fun!

I think, therefore I am. I think? - "George Carlin"
My Website: Indie Game Programming

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And I almost forgot. When you run into a problem, and the client/server isn't working, what then?

http://www.wireshark.org/

Trust me, spend the afternoon learning to use this. It will pay for itself 10 times over smile.png

I think, therefore I am. I think? - "George Carlin"
My Website: Indie Game Programming

My Twitter: https://twitter.com/indieprogram

My Book: http://amzn.com/1305076532

Glass_Knife that is awesome mate :), well we have been given a pong game which needs to be converted so, I understand most of it now, but yea, still the inputStream and outputStream is alittle confusing, but I'm going to do some hard debugging and testing using the oracle network tutorial which is a knock knock server :) should help me out

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