I just wondering what java does when we call close on the inputStream and outStream associated with a socket. What is the difference from the close call on the socket, i.e Socket.close().
if we just close the io stream on the socket, but not close the socket, can we reopen the io stream on the socket again?
Thanks in advance!
From the java api documentation for Socket:
public void close() throws IOException Closes this socket. Any thread currently blocked in an I/O operation upon this socket will throw a SocketException.
Once a socket has been closed, it is not available for further networking use (i.e. can't be reconnected or rebound). A new socket needs to be created.
Closing this socket will also close the socket's InputStream and OutputStream.
If this socket has an associated channel then the channel is closed as well.
Closing the InputStream of the Socket will lead to the closing of the Socket. The same goes for closing the OutputStream of the Socket.
From the java api documentation for Socket#getInputStream()
Closing the returned InputStream will close the associated socket.
Check the API documentation, it is there for a reason.
Generally, close() should only be done by the party responsible for open(). That way, the open-close pair can be managed easier. Since we can't open socket i/o streams (conceptually they are open as soon as socket is open), we should not close them. The party that opened the socket should close the socket though.
Sometimes you have no choice, you pass an open stream to a method, and the method decides it has the right to close the stream. You can pass a wrapper stream so that close() doesn't have effect.
If you really want to, you can close socket i/o streams without closing the socket, but they cannot be re-open once closed.
shutdownInput() - pretty useless. If an application doesn't need any more input, simply stop reading - there is no point to invoke this method. Stop receiving data from peer. If the peer tries to send data to us, it may receive error ("connection reset")
shutdownOutput() - can be very useful, it flushes all the data to the peer, and sends a FIN signal. The connection is now half-closed. The peer can still send data, and we can still read it, because that direction is still open.
These two methods are not used often. Normally Socket.close() is called to end the whole connection.
You should close the outermost output stream you have created from the socket. That will flush it. Closing either the socket or the input stream doesn't do that so it isn't adequate. Having closed that output stream you don't need to do anything else.