UDP - Java Network Programming - page 423

socket . send ( outgoing );
DatagramPacket incoming
= new DatagramPacket ( new byte [ bufferSize ], bufferSize );
// next line blocks until the response is received
socket . receive ( incoming );
int numBytes = incoming . getLength ();
byte [] response = new byte [ numBytes ];
System . arraycopy ( incoming . getData (), 0 , response , 0 , numBytes );
return response ;
} catch ( IOException ex ) {
return null ;
}
}
public static void main ( String [] args ) {
InetAddress host ;
int port = 0 ;
try {
host = InetAddress . getByName ( args [ 0 ]);
port = Integer . parseInt ( args [ 1 ]);
} catch ( RuntimeException | UnknownHostException ex ) {
System . out . println ( "Usage: java UDPPoke host port" );
return ;
}
try {
UDPPoke poker = new UDPPoke ( host , port );
byte [] response = poker . poke ();
if ( response == null ) {
System . out . println ( "No response within allotted time" );
return ;
}
String result = new String ( response , "US-ASCII" );
System . out . println ( result );
} catch ( UnsupportedEncodingException ex ) {
// Really shouldn't happen
ex . printStackTrace ();
}
}
}
For example, this connects to a daytime server over UDP:
$ java UDPPoke rama.poly.edu 13
Sun Oct 3 13:04:22 2009
This connects to a chargen server:
$ java UDPPoke rama.poly.edu 19
123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuv