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 address InetAddress

• public static InetAddress getByName(String host)
• InerAddress a InetAddress.getByName(compserv1.c
  s.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
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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.

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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.

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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.

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ServerSocket

•  Socket accept()           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.

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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 new ServerSocket(PORT)
  
• try
• // Block until a connection occurs
• Socket socket listen_sock.accept()
• try
• // Connection accepted
• BufferedReader in new BufferedReader(
• new InputStreamReader( socket.getInputStream())
• )

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• // 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()

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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(localho
  st)
• // Create a socket and connect to remote server
• Socket socket new Socket(addr,
  EchoServer.PORT)
• try
• // Get the input stream
• BufferedReader in new BufferedReader(
• new InputStreamReader(socket.getInputStream()))
  

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• // Get the output stream
• PrintWriter out new PrintWriter(
• new BufferedWriter(
• new OutputStreamWriter(
• socket.getOutputStream())
• ), true)
• for(int i 0 i lt 10 i )
• out.println(Hello " i)
• String str in.readLine()
• System.out.println(str)
• out.println("END")
• finally socket.close()

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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.

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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.

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UDP Echo Server example
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• // buffer to receive data
• byte buf new byte1000 // 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())

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• //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)