Referring to Java API Specifications http java sun

Referring to Java API Specifications http: //java. sun. com/j 2 se/1. 4. 1/docs/api

Java Network Programming

Representing IP address Inet. Address public static Inet. Address get. By. Name(String host) Iner. Address a = Inet. Address. get. By. Name(“compserv 1. cs. sunysb. edu”); Iner. Address a = Inet. Address. get. By. Name(“localhost”);

TCP Sockets Client Server accept() Socket Server. Socket

Sockets Client Server. Socket connect()

Sockets Server Client Server. Socket connect() Socket

Sockets Client Server accept() Server. Socket

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.

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

Server. Socket • Server. Socket() Creates an unbound server socket. • Server. Socket(int port) Creates a server socket, bound to the port. • Server. Socket(int port, int backlog) Creates a server socket and binds it to the local port number, with the backlog. • Server. Socket(int port, int backlog, Inet. Address bind. Addr) Create a server with the port, listen backlog, and local IP address to bind to.

Server. Socket… • Socket accept() Listens for a connection and accepts it. • void bind(Socket. Address endpoint) Binds to an address. • void bind(Socket. Address endpoint, int backlog) Binds to an address with backlog limit. • void close() Closes this socket.

TCP Echo Server (again!)

import java. io. *; import java. net. *; public class Echo. Server { public static final int PORT = 8080; public static void main(String[] args) throws IOException { Server. Socket listen_sock = new Server. Socket(PORT); try { // Block until a connection occurs: Socket socket = listen_sock. accept(); try { // Connection accepted: Buffered. Reader in = new Buffered. Reader( new Input. Stream. Reader( socket. get. Input. Stream()) );

// Output is automatically flushed by Print. Writer: Print. Writer out = new Print. Writer( new Buffered. Writer( new Output. Stream. Writer( socket. get. Output. Stream()) ) , true); // echo back and forth while (true) { String str = in. read. Line(); if (str. equals("END")) break; out. println(str); } } finally { System. out. println("closing. . . "); socket. close(); } } finally { listen_sock. close(); } }

TCP Echo Client

import java. net. *; import java. io. *; public class Echo. Client { public static void main(String[] args) throws IOException { Inet. Address addr = Inet. Address. get. By. Name(“localhost”); // Create a socket and connect to remote server Socket socket = new Socket(addr, Echo. Server. PORT); try { // Get the input stream Buffered. Reader in = new Buffered. Reader( new Input. Stream. Reader(socket. get. Input. Stream()));

// Get the output stream Print. Writer out = new Print. Writer( new Buffered. Writer( new Output. Stream. Writer( socket. get. Output. Stream()) ), true); for(int i = 0; i < 10; i ++) { out. println(“Hello " + i); String str = in. read. Line(); System. out. println(str); } out. println("END"); } finally {socket. close(); } }

Datagram. Socket • Datagram. Socket() – Constructs a datagram socket and binds it to any available port. • Datagram. Socket(int port) – Constructs a datagram socket and binds it to the specified port. • Datagram. Socket(int port, Inet. Address laddr) – Creates a datagram socket, bound to the specified local address. • Datagram. Socket(Socket. Address bindaddr) – Creates a datagram socket, bound to the specified local address.

Datagram. Packet • Datagram. Packet(byte[] buf, int length) – Constructs a Datagram. Packet for receiving packets. • Datagram. Packet(byte[] buf, int length, Inet. Address address, int port) – Constructs a datagram packet for sending packets to the specified address and port.

UDP Echo Server example

// buffer to receive data byte[] buf = new byte[1000]; // buffer // create packet for receiving Datagram. Packet recv_dp = new Datagram. Packet(buf, buf. length); // create socket for sending Datagram. Socket socket; try { socket = new Datagram. Socket(INPORT); while(true) { // Block until a datagram appears: socket. receive(recv_dp); // Extract the string received String str = new String(recv_dp. get. Data(), 0, recv_dp. get. Length());

//Construct the datagram to send Datagram. Packet echo = new Datagram. Packet( str. get. Bytes(0, str. length(), buf, 0), str. length, recv_dp. get. Address(), recv_dp. get. Port()); // send it back socket. send(echo); } } catch(Socket. Exception e) { System. err. println("Can't open socket"); System. exit(1); } catch(IOException e) { System. err. println("Communication error"); System. exit(1); }