import java.; import java.io.; public class LowPortScanner {

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

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

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

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)

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

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"); } } }

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"); } } }

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."); } } }

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."); }

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."); }

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]); } } }

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."); } } }

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); } } }

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

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" )

URL Methods • getProtocol( ) • getHost( ) • getPort( ) • getFile( ) • openConnection() returns URLConnection • URLConnection • getType() • getInputStream()

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();

Protocol Identifier Resource Name 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.

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

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

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.

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"); } }

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!")); } } }

import java.; import java.io.; public class LowPortScanner {