Java Reference
In-Depth Information
Note that the connection is returned a
java.net.Socket
object, the same as you used
for clients in the previous chapter. The daytime protocol requires the server (and only
the server) to talk, so get an
OutputStream
from the socket. Because the daytime protocol
requires text, chain this to an
OutputStreamWriter
:
OutputStream
out
=
connection
.
getOutputStream
();
Writer
writer
=
new
OutputStreamWriter
(
writer
,
"ASCII"
);
Now get the current time and write it onto the stream. The daytime protocol doesn't
require any particular format other than that it be human readable, so let Java pick for
you:
Date
now
=
new
Date
();
out
.
write
(
now
.
toString
()
+
"\r\n"
);
Do note, however, the use of a carriage return/linefeed pair to terminate the line. This
is almost always what you want in a network server. You should explicitly choose this
rather than using the system line separator, whether explicitly with
System.getProper
ty("line.separator")
or implicitly via a method such as
println()
.
Finally, flush the connection and close it:
out
.
flush
();
connection
.
close
();
You won't always have to close the connection after just one write. Many protocols, dict
and HTTP 1.1 for instance, allow clients to send multiple requests over a single socket
and expect the server to send multiple responses. Some protocols such as FTP can even
hold a socket open indefinitely. However, the daytime protocol only allows a single
response.
If the client closes the connection while the server is still operating, the input and/or
output streams that connect the server to the client throw an
InterruptedIOExcep
tion
on the next read or write. In either case, the server should then get ready to process
the next incoming connection.
Of course, you'll want to do all this repeatedly, so you'll put this all inside a loop. Each
pass through the loop invokes the
accept()
method once. This returns a
Socket
object
representing the connection between the remote client and the local server. Interaction
with the client takes place through this
Socket
object. For example:
ServerSocket
server
=
new
ServerSocket
(
port
);
while
(
true
)
{
try
(
Socket
connection
=
server
.
accept
())
{
Writer
out
=
new
OutputStreamWriter
(
connection
.
getOutputStream
());
Date
now
=
new
Date
();
out
.
write
(
now
.
toString
()
+
"\r\n"
);
out
.
flush
();
}
catch
(
IOException
ex
)
{
// problem with one client; don't shut down the server
