Physics Simulation       Lecture 13B Networking Internet Basics IP - Datagrams TCP - UDP Application Layer Ports Java Networking URL InetAddress Sockets Client-Server RMI Exercises Lectures 1A: Introduction 1B: Java Intro 2A: BuildingBlocks 2B: Objects 3A: More Objects 3B: Exceptions        & Threads 4A: Waves 4B: Nuclear &        Particle 5A: AWT 5B: More AWT       & Graphics 6A:Detectors &       Simulation 6B: LHC/Atlas &      RandomSims     7A: Swing 7B: Java2D 8A: Java Apps 8B: Dialogs &     MoreClasses 9A: Java I/O 9B: Utilities,         Unicode 10A: More     Threading 10B: File     Handling 11A: Array,Print,     Images 11B: SimplePhysics     Simulation 12A: Tips &     Techniques 12B: More Tips &     Techniques 13A: Satellite     Simulations 13B: Intro to Java     Networking 14A: Java Servers 14B: HTTP Server 15A: ServerClient 15B: ServerClient    Expt.Simulation 16A: Course           Review 16B: ExerciseTest         Discussion     Contacts     Description     Exercises     Index     Outline     Q&A     Resources     StudentInfoForm     Student Pages     What's New

Home : Lectures : Lecture 13B : Sockets Sockets Sockets provide connections between applications that allow streams of data to flow. Sockets are fairly straightforward to setup in Java. Java provides 2 kinds of sockets: Socket: connection-oriented protocol (i.e. behaves like a telephone line, the connection remains even when no one is talking) DatagramSocket: a connectionless protocol datagram packets no attempt to maintain a fixed connection does not keep packets in order or guarantee their arrival. We will talk more about sockets in a later lecture. Here is a demo showing a socket used to recieve the data from a socket connected to port 37 on a remote computer. On some machines this port provides a current time service. DateAtHost.java   import java.net.*; import java.io.*; public class DateAtHost extends java.util.Date {   static int timePort = 37;   static final long offset= 2208988800L;//Seconds from century                                         //to Jan 1,1970 00:00GMT   public DateAtHost( String host ) throws IOException {    this( host, timePort );   }   public DateAtHost( String host, int port ) throws IOException {     // Open a socket to this host on port 37     Socket sock = new Socket( host, port );     // Open an input stream to this socket.     DataInputStream din =       new DataInputStream(sock.getInputStream() );     // Now read the integer time value from the socket stream.     int time = din.readInt();     sock.close();     setTime( (((1L << 32) + time) - offset) * 1000 ) ;   }   // Example usage: java DateAtHost helio.ora.com   public static void main (String [] args) {     try {       System.out.println( new DateAtHost( args[0] ) );     } catch (UnknownHostException e){       System.out.println("Host " + args[0] +" is unknown.");     } catch (IOException e){       System.out.println("IO Exception");     }   } }

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