1 Java networking

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3
Addressing IP address and Port

• Sending to application (process) on remote
  computer
• Identify source, dest. computers by IP (Internet
  Protocol) address
• Include source and destination port numbers
• Ports identify the application (process)
• 16 bit number
• Well-known ports 0..1023 are reserved ports
• E.g. HTTP 80, DNS 53,
• Custom Use gt 1024
• Two main transport protocols TCP and UDP
  protocols
• Both use ports to identify destination process,
  but differently

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Ports and Processes TCP vs. UDP
10.0.2.83
10.0.2.177
TCP Client Appl., port 2222
TCP Server Appl., port 80
TCP
TCP
UDP Server Appl., port 53
UDP Client Appl., port 4444
UDP
UDP
Whats the difference? Add another client to see
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Ports and Processes TCP vs. UDP
10.0.1.1
10.0.2.83
TCP Client Appl., port 1111
TCP
UDP Client Appl., port 2222
UDP
TCP Server process for (10.0.1.1,1111,80)
TCP
TCP Server process for (10.2.2.2,3333,80)
10.2.2.2
UDP Server Appl., port 5555
UDP
TCP Client Appl., port 3333
TCP
UDP Client Appl., port 4444
UDP same server process handles all requests to
same port
UDP
6
TCP vs UDP

• TCP Transmission Control Protocol
• Connection - based
• Reliable (arrival, ordering)
• Transmission guaranteed, or error is reported.
• Communication in input / output streams.
• Example
• HTTP, FTP, SMTP, TELNET,
• UDP User Datagram Protocol
• Not connection based
• Non Reliable.
• Communication with Datagrams (chunks of data)
• The order of Datagrams is not guaranteed.
• Example
• Radio, Clock Server, Ping, Video stream.

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TCP
8
Sockets

• Socket End point of a two-way communication link
  between two programs running on the network.
• Socket is a software abstraction to represent the
  terminals of a connection.
• A socket is bound to a port number so that the
  TCP layer can identify the application that data
  is destined to be sent.
• Two stream-based Socket classes
• ServerSocket For server
• On connection returns a new Socket
• Socket For client
• Have getInputStream() and getOutputStream()
  functions

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Socket Connection for Client

• Basic program flow for Client
• Open Socket
• Open an input stream and output stream to the
  socket
• Read from and write to the stream according to
  the servers protocol
• Close the streams
• Close the socket
• Only step 3 differs from client to client,
  depending on the server

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Socket Client Example

• import java.io.
• import java.net.
• public class SocketClient
• public static void main(Stringargs) throws
  IOException
• Socket socket null PrintWriter out null
  BufferedReader in null String host
  "localhost"
• try
• socket new Socket(localhost,7777) //
  Port number 7777
• out new PrintWriter(socket.getOutputStream(),
  true)
• in new BufferedReader(new
  InputStreamReader(socket.getInputStream()))
  
• // client code..
• catch (UnknownHostException e)
• System.err.println("Dont know host "host)
  System.exit(-1)
• catch (IOException e)
• System.err.println("Cannot get IO for
  connection to "host) System.exit(-1)
• finally
• // close connection (Order important)

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Socket Connection for Server

• Basic program flow for Server
• Create a ServerSocket
• Call ServerSocket.accept() to get a Socket
  connection
• Open input stream and output stream to that
  socket
• Read from and write to streams according to the
  Protocol
• Close the streams
• Close the socket
• ( Optional Return to 2 to get another connection
  )
• For Server allowing multiple connections, 3-6
  must be in another thread

12
Socket Server Example

• import java.net.
• import java.io.
• public class SocketServer
• public static void main(Stringargs) throws
  IOException
• ServerSocket serverSocket null
  PrintWriter out null BufferedReader in null
• try
• serverSocket new ServerSocket(4444)
• catch (IOException e)
• System.err.println("Cannot listen on port
  4444") System.exit(-1)
• Socket clientSocket null
• try
• clientSocket serverSocket.accept()
• out new PrintWriter(clientSocket.getOutputStr
  eam(),true)
• in new BufferedReader(new
  InputStreamReader(clientSocket.getInputStream()
  ))
• // server code here.

13
Supporting Multiple Clients

• In the Server Side
• while (true)
• accept a connection
• create a thread to deal with the client

14
Server Thread - MultiServerThread

• import java.net.
• import java.io.
• public class MultiServerThread extends Thread
• private Socket socket null
• public MultiServerThread(Socket socket)
• this.socket socket
• public void run()
• BufferedReader in null PrintWriter out
  null
• try
• in new BufferedReader(new
  InputStreamReader(socket.getInputStream())
  )
• out new PrintWriter(socket.getOutputStr
  eam(),true)
• String inputLine
• while ((inputLinein.readLine())!null)
• // processing code here...
• catch (IOException e)
• e.printStackTrace()

15
Server Class - MultiServer

• import java.net.
• import java.io.
• public class MultiServer
• public static void main(Stringargs) throws
  IOException
• ServerSocket serverSocket null
• boolean listening true
• try
• serverSocket new ServerSocket(4444)
• catch (IOException e)
• System.err.println("Could not listen on port
  4444")
• System.exit(-1)
• while (listening)
• new MultiServerThread(serverSocket.accept()).st
  art()
• serverSocket.close()

16
UDP
17
Identifying a Machine

• import java.net.
• public class WhoAmI
• public static void main(String args) throws
  Exception
• if(args.length ! 1)
• System.err.println("Usage WhoAmI
  MachineName")
• System.exit(1)
• InetAddress a InetAddress.getByName(args0)
  
• System.out.println(a)
• To run
• java WhoAmI myMachinemyMachine/127.0.0.1

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Remote Connections

• Identifying a Machine
• IP (Internet Protocol) adress
• DNS (Domain Name System) www.cs.biu.ac.il
• Dotted Quad Form 123.255.28.120
• InetAddress iaInetAddress.getByName()
• Local Host (for testing)
• All these three forms connect to local host
• InetAddress iaInetAddress.getByName(null)
• InetAddress iaInetAddress.getByName(localhost)
  
• InetAddress iaInetAddress.getByName(127.0.0.1)
  
• InetAddress iaInetAddress.getLocalHost()

19
UDP communication

• UDP Delivers independent packages whose arrival
  and order of arrival is not guaranteed.
• Packets sent by UDP protocol are called
  Datagrams.
• DataGram Is an independent, self-contained
  message sent over the network whose arrival, and
  content are not guaranteed.
• Classes for UDP connection
• DatagramPacket
• DatagramSocket
• MulticastSocket

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Example UDPServer

• import java.io.
• import java.net.
• import java.util.
• public class UDPServerExample
• protected DatagramSocket socket null
  protected BufferedReader in null protected
  boolean moreQuotes true
• public void run() throws IOException
• socket new DatagramSocket(4445)
• try
• byte buf new byte256
• // Request
• DatagramPacket packet new
  DatagramPacket(buf,buf.length)
• socket.receive(packet)
• // generate Response
• String response Response
• buf response.getBytes()
• // Send the response
• InetAddress address
  packet.getAddress()
• int port packet.getPort()
• packet new DatagramPacket(buf,buf.leng
  th,address,port)

21
Example UDPClient

• import java.io.
• import java.net.
• import java.util.
• public class UDPClientExample
• public static void main(Stringargs) throws
  IOException
• try
• DatagramSocket socket new DatagramSocket()
• byte bufnew byte256
• InetAddress address InetAddress.getByName(10
  .0.2.83)
• DatagramPacket packet
• new DatagramPacket(buf,buf.length,address,4445
  )
• socket.send(packet)
• packetnew DatagramPacket(buf,buf.length)
• socket.receive(packet)
• String receivednew String(packet.getData())
• System.out.println("Received "received)
• finally