Referring to Java API Specifications

1. Referring to Java API Specifications http://java.sun.com/j2se/1.4.1/docs/api

2. Java Network Programming

3. Representing IP addressInetAddress public static InetAddressgetByName(String host) InerAddress a = InetAddress.getByName(“compserv1.cs.sunysb.edu”); InerAddress a = InetAddress.getByName(“localhost”);

4. TCP Sockets Server Client accept() ServerSocket Socket

5. Sockets Server Client ServerSocket Socket connect()

6. Sockets Server Client ServerSocket connect() Socket Socket

7. Sockets Server Client accept() ServerSocket Socket Socket

8. Socket • public Socket() • Creates an unconnected socket. • public Socket(String host, int port) • Creates a stream (TCP) socket and connects it to the specified port number on the named host.

9. Socket… • void bind(SocketAddress bindpoint)          Binds the socket to a local address. •  void close()          Closes this socket. •  void connect(SocketAddress endpoint)          Connects this socket to the server. •  void connect(SocketAddress endpoint, int timeout)          Connects this socket to the server with a timeout.

10. ServerSocket • ServerSocket()          Creates an unbound server socket. • ServerSocket(int port)          Creates a server socket, bound to the port. • ServerSocket(int port, int backlog)          Creates a server socket and binds it to the local port number, with the backlog. • ServerSocket(int port, int backlog, InetAddress bindAddr)          Create a server with the port, listen backlog, and local IP address to bind to.

11. ServerSocket… • Socketaccept()          Listens for a connection and accepts it. •  void bind(SocketAddress endpoint)          Binds to an address. •  void bind(SocketAddress endpoint, int backlog)          Binds to an address with backlog limit. •  void close()          Closes this socket.

12. TCP Echo Server (again!)

13. import java.io.*; import java.net.*; public class EchoServer { public static final int PORT = 8080; public static void main(String[] args) throws IOException { ServerSocket listen_sock = newServerSocket(PORT); try { // Block until a connection occurs: Socket socket = listen_sock.accept(); try { // Connection accepted: BufferedReader in = new BufferedReader( new InputStreamReader( socket.getInputStream()) );

14. // Output is automatically flushed by PrintWriter: PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter( socket.getOutputStream()) ) , true); // echo back and forth while (true) { String str = in.readLine(); if (str.equals("END")) break; out.println(str); } } finally { System.out.println("closing..."); socket.close(); } } finally { listen_sock.close(); } }

15. TCP Echo Client

16. import java.net.*; import java.io.*; public class EchoClient { public static void main(String[] args) throws IOException { InetAddress addr = InetAddress.getByName(“localhost”); // Create a socket and connect to remote server Socket socket = newSocket(addr, EchoServer.PORT); try { // Get the input stream BufferedReader in = new BufferedReader( new InputStreamReader(socket.getInputStream()));

17. // Get the output stream PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter( socket.getOutputStream()) ), true); for(int i = 0; i < 10; i ++) { out.println(“Hello " + i); String str = in.readLine(); System.out.println(str); } out.println("END"); } finally {socket.close(); } }

18. DatagramSocket • DatagramSocket() • Constructs a datagram socket and binds it to any available port. • DatagramSocket(int port) • Constructs a datagram socket and binds it to the specified port. • DatagramSocket(int port, InetAddress laddr) • Creates a datagram socket, bound to the specified local address. • DatagramSocket(SocketAddress bindaddr) • Creates a datagram socket, bound to the specified local address.

19. DatagramPacket • DatagramPacket(byte[] buf, int length) • Constructs a DatagramPacket for receiving packets. • DatagramPacket(byte[] buf, int length, InetAddress address, int port) • Constructs a datagram packet for sending packets to the specified address and port.

20. UDP Echo Server example

21. // buffer to receive data byte[] buf = new byte[1000]; // buffer // create packet for receiving DatagramPacket recv_dp = new DatagramPacket(buf, buf.length); // create socket for sending DatagramSocket socket; try { socket = new DatagramSocket(INPORT); while(true) { // Block until a datagram appears: socket.receive(recv_dp); // Extract the string received String str = new String(recv_dp.getData(), 0, recv_dp.getLength());

22. //Construct the datagram to send DatagramPacket echo = new DatagramPacket( str.getBytes(0, str.length(), buf, 0), str.length, recv_dp.getAddress(), recv_dp.getPort()); // send it back socket.send(echo); } } catch(SocketException e) { System.err.println("Can't open socket"); System.exit(1); } catch(IOException e) { System.err.println("Communication error"); System.exit(1); }