Using TCP sockets in Java

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Using TCP sockets in Java

• Created by
• M Bateman, A Ruddle C Allison
• As part of the TCP View project

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Overview

• TCP socket
• Client/Server
• Multithread server
• Thread pooling server
• Alternate thread pooling server

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TCP Provides

• Process to process communication
• Use tuple of IP address port
• Reliable
• In order
• Socket is one end-point of a two way connection
  link

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TCP Socket Operations
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TCP in Java
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TCP in Java

• Implemented in java.net.
• Two main classes
• java.net.ServerSocket - for server
• java.net.Socket - for client
• Provides abstractions over
• Socket and connect operations
• Bind, listen accept
• Remember to close the socket at the end

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ServerSocket

• Constructors
• ServerSocket (port)
• ServerSocket (port, backlog)
• ServerSocket (port, backlog, bindAddress)
• Where
• port the TCP port to listen on
• backlog TCP queue length
• bindAddress interface to use (else all)

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Socket

• Construction
• Two important constructors
• Socket () random local port
• Socket (host, port) remote host and port
• Is the end point for communication
• Used in both the client and server
• Client connects to ServerSocket
• ServerSocket returns Socket for communications

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Daytime server

• import java.net.
• import java.io.
• public class DTServer
• public static void main (String argv)
• int dayTimePort 13
• try
• ServerSocket dtserver new ServerSocket
  (dayTimePort)
• while (Socket con dtserver.accept ())
• PrintWriter out new PrintWriter
  (con.getOutputStream (), true)
• Date now new Date ()
• out.println (now.toString ())
• con.close ()
• catch (Exception e)

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Daytime client

• import java.net.
• import java.io.
• public class DTClient
• public static void main (String argv)
• int dayTimePort 13
• try
• Socket con new Socket (argv0,
  dayTimePort)
• InputStream is con.getInputStream ()
• BufferedReader br new BufferedReader (new
  InputStreamReader (is))
• String time br.readLine ()
• System.out.println (The time at argv0
  is time)
• con.close ()
• catch (Exception e)

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Issues

• Can only deal with one request at once
• Performance
• Have to wait until the guy in front has finished
  with the server

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Solution Threads

• Thread theory not covered here
• Basically allows server to do more than one thing
  at once (see operating system course to find out
  why this isnt true)
• Two ways
• Extend java.lang.Thread
• Implement java.lang.Runnable
• Override public void run ()

• public class TThread extend Thread
• public void run ()
• for (int i 0 i lt 100 i)
• System.out.println (i)
• public static void main (String argv)
• new TThread ().start ()

public class RThread implements Runnable
public void run () for (int i 0 i lt
100 i) System.out.println (i)
public static void main (String argv)
new Thread (new TThread ()).start ()
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Multithreaded Daytime

• import java.net.
• import java.io.
• public class DTServer
• public static void main (String argv)
• int dayTimePort 13
• try
• ServerSocket dtserver new ServerSocket
  (dayTimePort)
• while (Socket con dtserver.accept ())
• DTThread dtthread new DTThread () //
  create the new thread
• dtthread.setSocket (con)
• dtthread.start () // start the thread now
• catch (Exception e)

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Daytime Thread

• import java.net.
• public class DTThread extends Thread
• Socket con null
• public void setSocket (Socket con)
• this.con con
• public void run () // Important work done here
• PrintWriter out new PrintWriter
  (con.getOutputStream (), true)
• Date now new Date ()
• out.println (now.toString ())
• con.close ()

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Issues

• Performance
• Thread creation at client connection
• Creating threads takes time
• Possible deadlock
• Due to multithreaded

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Thread Pools - Basic

• import java.net.
• import java.io.
• public class DTServer
• public static void main (String argv)
• int dayTimePort 13
• List list Collections.synchronizedList(new
  LinkedList())
• for (int i 0 i lt 10 i ) list.add (new
  DTThread ()) // create 10 threads
• try
• ServerSocket dtserver new ServerSocket
  (dayTimePort)
• while (Socket con dtserver.accept ())
• DTThread dtthread (DTThread)list.remove
  (0)
• dtthread.setSocket (con)
• dtthread.start () // start the thread now
• list.add (new DTThread ()) // create a
  thread to create the one we just used
• catch (Exception e)

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Issues

• Possible deadlock
• Resource thrashing
• Concurrency errors
• Thread leakage
• Request overload
• Performance
• Thread creation still has to be performed in the
  main loop

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Pool Alternative Implementation

• Create pool as before
• Create thread which makes sure the pool has n
  thread waiting
• On connection take thread from the pool
• The above thread makes sure there are always
  threads in the pool waiting to be used

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Summary