1. import java.net.*; import java.io.*; public class LowPortScanner { public static void main(String[] args) { String host = "localhost"; if (args.length > 0) { host = args[0]; } for (int i = 1; i < 1024; i++) { try { Socket s = new Socket(host, i); System.out.println("There is a server on port " + i + " of " + host); } catch (UnknownHostException ex) { System.err.println(ex); break; } catch (IOException ex) { // must not be a server on this port } } // end for } // end main } // end PortScanner

2. import java.net.*; import java.io.*; public class SocketInfo { public static void main(String[] args) { for (int i = 0; i < args.length; i++) { try { Socket theSocket = new Socket(args[i], 80); System.out.println("Connected to " + theSocket.getInetAddress() + " on port " + theSocket.getPort() + " from port " + theSocket.getLocalPort() + " of " + theSocket.getLocalAddress()); } // end try catch (UnknownHostException ex) { System.err.println("I can't find " + args[i]); } catch (SocketException ex) { System.err.println("Could not connect to " + args[i]); } catch (IOException ex) { System.err.println(ex); } } // end for } // end main } // end SocketInfo

3. Multicast Sockets MulticastSocket : This kind of socket is used on the client-side to listen for packets that the server broadcasts to multiple clients.

7. InetAddress Class Represents an IP address Can convert domain name to IP address –Performs DNS lookup Getting an InetAddress object –getLocalHost() –getByName(String host) –getByAddress(byte[] addr)

8. InetAddress is a factory You can’t create InetAddress objects by invoking the InetAddress constructor Instead, invoke static methods of the InetAddress class These methods return either a Inet4Address or a Inet6Address –both of which extend InetAddress The factory design pattern delegates responsibility for what class of object to create to the factory

9. import java.net.*; public class OReillyByName { public static void main (String[] args) { try { InetAddress address = InetAddress.getByName("www.oreilly.com"); System.out.println(address); } catch (UnknownHostException ex) { System.out.println("Could not find www.oreilly.com"); }

10. import java.net.*; public class AllAddressesOfMicrosoft { public static void main (String[] args) { try { InetAddress[] addresses = InetAddress.getAllByName("www.microsoft.com"); for (int i = 0; i < addresses.length; i++) { System.out.println(addresses[i]); } catch (UnknownHostException ex) { System.out.println("Could not find www.microsoft.com"); }

11. import java.net.*; public class MyAddress { public static void main(String[] args) { try { InetAddress me = InetAddress.getLocalHost(); String dottedQuad = me.getHostAddress(); System.out.println("My address is " + dottedQuad); } catch (UnknownHostException ex) { System.out.println("I'm sorry. I don't know my own address."); }

12. import java.net.*; public class IPCharacteristics { public static void main(String[] args) { try { InetAddress address = InetAddress.getByName(args[0]); if (address.isAnyLocalAddress()) { System.out.println(address + " is a wildcard address."); } if (address.isLoopbackAddress()) { System.out.println(address + " is loopback address."); } if (address.isLinkLocalAddress()) { System.out.println(address + " is a link-local address."); }

13. else if (address.isSiteLocalAddress()) { System.out.println(address + " is a site-local address."); } else { System.out.println(address + " is a global address."); } if (address.isMulticastAddress()) { if (address.isMCGlobal()) { System.out.println(address + " is a global multicast address."); } else if (address.isMCOrgLocal()) { System.out.println(address + " is an organization wide multicast address."); } else if (address.isMCSiteLocal()) { System.out.println(address + " is a site wide multicast address."); } else if (address.isMCLinkLocal()) { System.out.println(address + " is a subnet wide multicast address."); }

14. else if (address.isMCNodeLocal()) { System.out.println(address + " is an interface-local multicast address."); } else { System.out.println(address + " is an unknown multicast address type."); } } else { System.out.println(address + " is a unicast address."); } } catch (UnknownHostException ex) { System.err.println("Could not resolve " + args[0]); }

15. import java.net.*; public class IBiblioAliases { public static void main (String args[]) { try { InetAddress ibiblio = InetAddress.getByName("www.ibiblio.org"); InetAddress helios = InetAddress.getByName("helios.metalab.unc.edu"); if (ibiblio.equals(helios)) { System.out.println ("www.ibiblio.org is the same as helios.metalab.unc.edu"); } else { System.out.println ("www.ibiblio.org is not the same as helios.metalab.unc.edu"); } catch (UnknownHostException ex) { System.out.println("Host lookup failed."); }

16. import java.net.*; import java.util.*; public class InterfaceLister { public static void main(String[] args) throws Exception { Enumeration interfaces = NetworkInterface.getNetworkInterfaces(); while (interfaces.hasMoreElements()) { NetworkInterface ni = (NetworkInterface) interfaces.nextElement(); System.out.println(ni); } }

17. URL Class Provides high-level access to network data Abstracts the notion of a connection Constructor opens network connection –To resource named by URL final class - Uses protocol handlers (strategy design pattern) with URL context to select

18. URL Constructors URL( fullURL ) –URL( "http://www.cs.umd.edu/class/index.html" ) URL( baseURL, relativeURL ) –URL base = new URL("http://www.cs.umd.edu/" ); –URL class = new URL( base, "/class/index.html " ); URL( protocol, baseURL, relativeURL ) –URL( "http", www.cs.umd.edu, "/class/index.html" ) URL( protocol, baseURL, port, relativeURL ) –URL( "http", www.cs.umd.edu, 80,"/class/index.html" )

19. URL Methods getProtocol( ) getHost( ) getPort( ) getFile( ) openConnection() returns URLConnection URLConnection –getType() –getInputStream()

20. URL Reader URLConnection connection = url.openConnection(); System.out.println("Type : " + connection.getContentType()); BufferedReader in = new BufferedReader( new InputStreamReader( connection.getInputStream())); String inputLine; while ((inputLine = in.readLine()) != null) System.out.println(inputLine); in.close();

21. Manipulating URLs URL is an acronym for Uniform Resource Locator and is a reference (an address) to a resource on the Internet. Sample structure of a URL. The resource name part may contain: host name, file name, port number(optional) and reference (optional) http://java.sun.com you can create a URL object in Java from an absolute URL or a relative URL. The URL class provides several methods implemented on URL objects. You can get the protocol, host name, port number, and filename from a URL. Protocol Identifier Resource Name

22. Example code import java.net.*; import java.io.*; public class ParseURL { public static void main(String[] args) throws Exception { URL aURL = new URL("http://java.sun.com:80/docs/books/" + "tutorial/index.html#DOWNLOADING"); System.out.println("protocol = " + aURL.getProtocol()); System.out.println("host = " + aURL.getHost()); System.out.println("filename = " + aURL.getFile()); System.out.println("port = " + aURL.getPort()); System.out.println("ref = " + aURL.getRef()); } Output of the above code: protocol = http host = java.sun.com filename = /docs/books/tutorial/index.html port = 80 ref = DOWNLOADING

23. Connecting with a URL (1) openStream() : returns a java.io.InputStream object, from which you can read easily as reading from an input stream. It may throw an IOException Example code import java.net.*; import java.io.*; public class ReadURL { public static void main(String[] args) throws Exception { URL osu = new URL("http://www.osu.edu/"); BufferedReader in = new BufferedReader( new InputStreamReader(osu.openStream())); String inputLine; while ((inputLine = in.readLine()) != null) System.out.println(inputLine); in.close(); } This prints out the source code for the webpage www.osu.edu

24. Connecting with a URL (2) openConnection() : Returns a URLConnection object that represents a connection to the remote object referred to by the URL. It may throws an IOException try { URL osu = new URL("http://www.osu.edu/"); URLConnection osuConnection = osu.openConnection(); } catch (MalformedURLException e) { // new URL() failed... } catch (IOException e) {... } The URLConnection class provides many methods to communicate with the URL, such as reading and writing.

25. private static void testProtocol(String url) { try { URL u = new URL(url); System.out.println(u.getProtocol() + " is supported"); } catch (MalformedURLException ex) { String protocol = url.substring(0, url.indexOf(':')); System.out.println(protocol + " is not supported"); } }

26. import java.net.*; import java.applet.*; import java.awt.*; public class RelativeURLTest extends Applet { public void init () { try { URL base = this.getDocumentBase(); URL relative = new URL(base, "mailinglists.html"); this.setLayout(new GridLayout(2,1)); this.add(new Label(base.toString())); this.add(new Label(relative.toString())); } catch (MalformedURLException ex) { this.add(new Label("This shouldn't happen!")); } }