Time Query NIO Example
This example asks a list of hosts what time it is. It's a simple, blocking program that demonstrates NIO socket channels (connection and reading), buffer handling, charsets, and regular expressions.
public class TimeQuery {
// The standard daytime port
private static int DAYTIME_PORT = 13;
// The port we'll actually use
private static int port = DAYTIME_PORT;
// Charset and decoder for US-ASCII
private static Charset charset = Charset.forName("US-ASCII");
private static CharsetDecoder decoder = charset.newDecoder();
// Direct byte buffer for reading
private static ByteBuffer dbuf = ByteBuffer.allocateDirect(1024);
// Ask the given host what time it is
private static void query(String host) throws IOException {
try (SocketChannel sc = SocketChannel.open()) {
InetSocketAddress isa = new InetSocketAddress(
InetAddress.getByName(host), port);
// Connect
sc.connect(isa);
// Read the time from the remote host. For simplicity we assume
// that the time comes back to us in a single packet, so that we
// only need to read once.
dbuf.clear();
sc.read(dbuf);
// Print the remote address and the received time
dbuf.flip();
CharBuffer cb = decoder.decode(dbuf);
System.out.print(isa + " : " + cb);
}
}
public static void main(String[] args) {
if (args.length < 1) {
System.err.println("Usage: java TimeQuery [port] host...");
return;
}
int firstArg = 0;
// If the first argument is a string of digits then we take that
// to be the port number
if (Pattern.matches("[0-9]+", args[0])) {
port = Integer.parseInt(args[0]);
firstArg = 1;
}
for (int i = firstArg; i < args.length; i++) {
String host = args[i];
try {
query(host);
} catch (IOException e) {
System.err.println(host + ": " + e);
e.printStackTrace();
}
}
}
}