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Network programming

Network programming. With JAVA. InetAddress class. The java.net.InetAddress class is Java's high-level representation of an IP address. It is used by most of the other networking classes including both a hostname and an IP address.

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Network programming

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  1. Network programming With JAVA

  2. InetAddress class • The java.net.InetAddress class is Java's high-level representation of an IP address. It is used by most of the other networking classes including both a hostname and an IP address. • Three static methods which are often used: getLocalHost(), getByName(String), getAllByName(String) Example InetAddress add1= InetAddress.getLocalHost(); InetAddress add2= InetAddress.getByName(“localhost”);

  3. getLocalhost() try { InetAddressaddress = InetAddress.getLocalHost(); System.out.println("My name is:”+address.getHostName()); System.out.println(“My Address is:”+address.getHostAddress()); } catch (UnknownHostException e) { System.out.println(“I don't know."); }

  4. getByName() ia = InetAddress.getByName("www.yahoo.com"); System.out.println(ia.getHostName()); System.out.println(ia.getHostAddress());

  5. getAllByName() InetAddress[] a = ia.getAllByName("www.google.com"); for (InetAddressiac : a) { System.out.println(iac.getHostAddress()); }

  6. Socket Programming

  7. Host 1 203.162.39.51 SOCKET Process A The transmitter & receiver establishes a TCP connection called socket. Socket enables data being transmitted & received on networks,. Port:4523 Process B Port:80 Host 2 10.6.8.111

  8. UDP Programming

  9. Java UDP Classes • Consist of two classes: DatagramPacket and DatagramSocket. • The DatagramPacket class stuffs bytes of data into UDP packets called datagrams and lets you un-stuff datagrams that you receive. • DatagramSocket class is used for sending and receiving UDP datagrams. • To send data, you put the data in a DatagramPacket and send using a DatagramSocket. • To receive data, you receive a DatagramPacket object from a DatagramSocket and then read the contents of the packet.

  10. DatagramPacket Constructor for sending: public DatagramPacket(byte[] data, int length, InetAddress destination, int port) public DatagramPacket(byte[] data,intoffset, int length, InetAddress destination, int port) String s = "This is a test."; byte[] data = s.getBytes(); try { InetAddressia = InetAddress.getByName("www.yahoo.com"); int port = 7; DatagramPacket dp = new DatagramPacket(data, data.length, ia, port); } …

  11. DatagramPacket Constructor for receiving: public DatagramPacket(byte[] buffer, int length) publicDatagramPacket(byte[] buffer, int offset, int length) Example: byte[] buffer = new byte[8192]; DatagramPacketdp = new DatagramPacket(buffer, buffer.length);

  12. The get methods • public InetAddressgetAddress() returns an InetAddress object containing the address of the remote host. • public intgetPort() returns an integer specifying the remote port. public byte[] getData() returns a byte array containing the data from the datagram. • public intgetLength() returns the number of bytes of data in the datagram.

  13. Example String s = "This is a test."; byte[] data = s.getBytes( ); try { InetAddressia = InetAddress.getByName("www.yahoo.com"); int port = 7; DatagramPacket dp = new DatagramPacket(data, data.length, ia, port); System.out.println("This packet is addressed to " + dp.getAddress() + " on port " + dp.getPort()); System.out.println("There are " + dp.getLength() + " bytes of data in the packet"); System.out.println( new String(dp.getData(), dp.getOffset(), dp.getLength())); } catch (UnknownHostException e) { System.err.println(e);}

  14. DatagramSocket class • To send or receive a DatagramPacket, one must open a datagram socket. • Adatagram socket is created and accessed through the DatagramSocket class.

  15. Constructors publicDatagramSocket() throwsSocketException • This constructor is used in a client that initiates a conversation with a server. • It also receive the datagrams that a server sends back to it. • A SocketException is thrown if the socket can't be created.

  16. Constructors Public DatagramSocket(int port) throwsSocketException • Creates a socket that listens on the particular port. • This constructor is used in a server that listens on a well-known port. • A SocketException is thrown if the socket can't be created. • There are two common reasons for the constructor to fail: • The specified port is already occupied, oryou are trying to connect to a port below 1,024.

  17. DatagramSocketMethods 1. public void send(DatagramPacket p) throwsIOException 2. public void receive(DatagramPacket p) throwsIOException 3. public void close() 4. publicintgetLocalPort()

  18. UDP Server Procedure • Create a UDP socket • Create a DatagramPacket to receive data • Receive data from Client. • Close UDP Socket DatagramSocket dsk= new DatagramSocket(1234); byte[] buffer= new byte[128]; DatagramPacket pk= new DatagramPacket(buffer, 128); dsk.receive(pk); System.out.println(“Client: ” + pk.getAddress() + ”:” + pk.getPort()); System.out.println(new String(buffer, 0, pk.getLength())); dsk.close();

  19. UDP Client Procedure • Create a UDP Socket • Create a DatagramPacketto send data • Send data • Close UDP Socket DatagramSocket dsk= new DatagramSocket(); String msg= “abc”; InetAddressaddr= InetAddress.getByName(“localhost”); DatagramPacket pk= new DatagramPacket(msg.getBytes(), msg.length(), addr, 1234); dsk.send(pk); dsk.close();

  20. TCP Programming

  21. TCP Sockets

  22. ServerSocket constructor publicServerSocket (intport) throwsIOException Example: To create a server socket to listen on port 1234: try { ServerSocket server = new ServerSocket(1234); … } catch (IOExceptionie) { // error catching code … }

  23. ServerSocketmethods • publicSocket accept() throwsIOException • publicvoid close() throwsIOException Example: To create a server socket to listen on port 1234 and accept connection request: try { ServerSocket server = new ServerSocket(1234); while (true) { Socket connection = server.accept(); provideService(connection); } } catch (IOExceptionie) { // error catching code … }

  24. Client Socket constructor Creates a TCP socket to the specified port on the specified host and attempts to connect to the remote host. 1.publicSocket(String host, int port) throwsUnknownHostException, IOException 2.publicSocket(InetAddressaddress, intport) throwsIOException

  25. Example try { Socket theSocket = new Socket(host, 80); System.out.println("Connected to " + theSocket.getInetAddress() + " on port " + theSocket.getPort() + " from port " + theSocket.getLocalPort() +" of “+ theSocket.getLocalAddress()); } catch (UnknownHostException ex) { System.err.println("I can't find " + host); } catch (SocketException ex) { System.err.println("Could not connect to " + host); } catch (IOException ex) { System.err.println(ex); }

  26. Data transmission Once connected, data will be transmitted/received : 1. publicInputStreamgetInputStream() throwsIOException 2. publicOutputStreamgetOutputStream() throwsIOException

  27. Example void doClientConnection(String computerName, intserverPort) { Socket connection; InputStreamin; OutputStreamout; try { connection = new Socket(computerName,serverPort); in = connection.getInputStream(); out = connection.getOutputStream(); } catch (IOException e) { // Error message return; } . . // Use the streams, in and out, to communicate with server. . try { connection.close(); } catch (IOException e) { } }

  28. TCP server procedures ServerSocketwelcomeSocket = new ServerSocket(6192); Socket connectionSocket= welcomeSocket.accept(); InputStream is= connectionSocket.getInputStream(); OutputStreamos= connectionSocket.getOutputStream(); byte[] buffer= new byte[128]; intlen= is.read(buffer); System.out.println(new String(buffer,0,len)); connectionSocket.close(); welcomeSocket.close();

  29. TCP client procedures Socket clientSocket = new Socket(host,6192); InputStream is= clientSocket.getInputStream(); OutputStreamos= connectionSocket.getOutputStream(); os.write(buffer); clientSocket.close();

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