If Socket
represents client side and ServerSocket
represents server side, why Socket.read
reads the data from server side? I'm really confused, Can you please clarify it to me?
(I post this answer because I always feel it's important to make the logic right.)
I suggest you take a look at the following sample.
http://docs.oracle.com/javase/tutorial/networking/sockets/clientServer.html
Admittedly, when carrying out TCP/IP communication, all the necessary information can be provided by the Socket
class alone for the sole purpose of communication. No matter it is on server side or client side.
As you can see from the above link, server side use the following code to acquire its own Socket
instance. That is, another socket is created on the same server local port and the client port pair.
Then, server use this Socket
instance to talk to the client.
And to make the picture complete, below code snippet shows client's Socket
instance.
So if Socket
can do it all already, why do we still need the ServerSocket
?
This is because of the working paradigm of communication over TCP/IP protocol.
When 2 programs talk over TCP/IP, usually one will passively listen/wait on a <IP:port>
and the other one will actively connect to it.
So you can see, at this very starting phase
of the communication, the 2 sides have very different behaviors. So 2 different classes are used to reflect this difference.
Socket
class encapsulates the behavior of the active side. (a.k.a. the client)ServerSocket
class encapsulates the behavior of the passive side (a.k.a. the server)Once the ServerSocket
accomplished its listening task and detected
an incoming connection, it will accept()
it and create a new Socket
instance to facilitate the communication.
Similarily, in java.nio
package, you will find ServerSocketChannel
and SocketChannel
classes. And still, they behave like this:
ServerSocketChannel -------------> SocketChannel
accept()
So, to some extent, I agree with @JohnK as he pointed out in the comment, it's more or less just a 6-letter difference
.