About ServerSockets and Sockets

Question

I m started networking in java and hava some questions.Can anyone clear these to me? What is the difference between sockets and server sockets? Is ServerSocket means something related to server?

Answer 1

Yes, I can explain it to you: A ServerSocket is the server-side socket. It needs an open port in your firewall and LISTEN for OTHER clients to connect to your computer. A 'normal' Socket just ASK a server for a connection. This does not need an open port in your firewall. Everything, that you do in the internet, requires, that your computer ASK a server in the internet, for a connection. But the server have to LISTEN for a connection. So with the ServerSocket, you can accept those requests and create a connection:

ServerSocket server = new ServerSocket(<port>);
Socket client = server.accept();

This is the serverside code and it creates a ServerSocket to listen for connection requests and create a normal Socket to use this connection. A Client application will connect like this:

Socket skt = new Socket(<ip>, <port>);

This will also create a socket, that can use the connection. But it requires a serverSocket, that accepts the connection request.

Hope, that helped you

Cydhra

P.S English is not my mother language, so I am sorry for mistakes.

EDIT:

Can u please explain me what does server.accept() do

This method waits until a client requests a connection. So if your application shall do something while waiting for connections, you should use a thread, because your programm will stop until server.accept() get a request.

server.accept() waits for a client requesting a connection with this server on the specified port. When a client requests such a connection, the accept()-Method will return a instance of Socket, that represent the Client. It contains the Input- and Output-Streams, that can be used to send and recieve data from the client.

Socket skt = new Socket(<port>, <ip>);

This is the code of the client, as I posted above. It also contains the input- and outputstreams. Everything, that you write in the OutputStream of one Socket, will be recieved by the InputStream, of the other Socket. The Sockets are like Files, with two ends: On one end, you write in, on the other side, you can read the written.