Java%20Networking%20TCP

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Java Networking TCP Yangjun Chen Dept. Business
Computing University of Winnipeg
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Ports

• In general, computers only have one Internet
  address, but computers usually need to
  communicate with more than one host at a time.
• Ports map incoming data to a particular
• process or application running on a computer,
• With every socket, there needs to be an
  associated port number
• Example - regular post. The IP address is like
  the street address while the port number would
  represent the house number.

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Sever - client communication

• A socket can be considered as a connection point.

port1
portN
SEVER
...
Sockets(Ipc, PortsM, port1)
IP address
IPs
IP address
IPc
Socketc(Ips, Port1, portM)
...
CLIENT
Port1
PortM
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Ports

• Ports can range in value from 1 to 65535, with
  ports 1 to 1023 being reserved for root access in
  Unix.
• On Windows NT, 95 and Macs, any user can listen
  on any port.
• Only one program can listen on a given TCP port
  at the same time.
• However, many remote hosts can connect to the
  same remote port.

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Internet Addresses

• Every computer on the net has an associated
  four-byte IP address that is unique. Usually
  represented in dotted quad format like
  148.131.31.1. where each byte is an unsigned
  value in the range of 0 to 255.
• Since numbers are hard to remember, these numbers
  are mapped into names like www.uwinnipeg.ca or
  www.umanitoba.ca.
• It's the numerical address that is fundamental,
  not the name. You can have multiple names that
  represent the same IP address.

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Internet Addresses

• java. net. InetAddress class are used to manage
  such addresses.
• Some are shown here -
• - InetAddress getByName(String host)
• - InetAddress getAllByName(String host)
• - InetAddress getLocalHost()
• - String getHostName()
• - byte getHostAddress()
• - boolean isMulticastAddress()

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Creating InetAddress Objects

• The InetAddress class is unusual in that it
  doesn't have a public constructor, so to create
  an object you would pass in the host
• name or string format of the dotted quad address
  into the static
• method
• InetAddress.getByName( )

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Creating InetAddress Objects
import java.net. class ibm public
static void min (String args) try
( InetAddress addresses
InetAddress.getAllEyName("
www.ibm.com") for (int i 0
iltaddresses.lengthi) System.out.println(a
ddressesi) //try catch
(UnknownHostException e) //main //class
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Creating InetAddress Objects

• To create an InetAddress that refers to your own
  machine use the static getLocalHost() method.
• try
• InetAddress me InetAddress.getLocalHost( )
• //try
• catch (UnknownHostException e)
• System.err.println( )
• //catch

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Parsing InetAddress

• Given an InetAddress, we might want to know the
  host name or it's IP address as a string or byte
  array.
• ImporL java.net.
• public class address
• public static void main(String args)
• try
• InetAddress me new netAddress.getLocalHost(
  ) System.out.println(me.getHostName())
  System.out.println(me.getHostAddress())

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Parsing InetAddress
byte quad me.getAddress() for(int i
0 i lt quad.length i) System.out.print(q
uadi .) System.out.println() //t
ry catch (UnknownHostException e) (
System.err.println(e) //catch //main
//class
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TCP

• TCP (Transmission Control Protocol)
• - a connection-based protocol that provides a
  reliable flow of data between two computers.
• - It allows retransmission of lost data.
• - It provides multiple paths through different
  routers in case one goes down.
• - Bytes are delivered in the order they are
  sent.
• Applications using TCP to communicate
• - HTTP, FTP, Telnet, etc.

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TCP

• Java networking classes use TCP
• java.net package provides the functionality for
  networking
• - java.net
• . URL()
• . URLConnection()
• . Socket()
• . SocketServer()

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Sockets

• Host's native networking s/w handles the
  splitting of data into packets on the
  transmitting side of a connection, and the
  reassembly of packets on the receiving side.
• Java programmers are presented with a higher
  level abstraction called a socket.

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Sockets

• A socket represents a reliable connection for
  data transmission between two hosts.
• Four fundamental operations
• - 1. Connect to a remote machine
• - 2. Send data
• - 3. Receive data
• - 4. Close the connection

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Establishing a Connection

• Accomplished through the class constructors
• - java.net.Socket()
• . client side implementation
• - java.net.ServerSocket()
• . server side implementation
• Each socket is associated with exactly one host.
• To connect to a different host, a new socket
  object must be created.

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Sending/Receiving Data

• Sending and Receiving data is accomplished with
  input and output streams.
• - public InputStream getInputStream()
• - public OutputStream getOutputStream()
• - both of these classes throw an IOException

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Closing a Connection

• There's a method to close a socket.
• - public synchronized void close()
• - this method throws an IOException as well.
• For a well behaved program, we need to close the
  I/O streams as well.
• Close any streams connected to a socket before
  closing the socket.
• - OutStream.close()
• - InStream.close()
• - Socket.close()

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Example EchoTest(l)
import java.io. import java.net., public
class EchoTest public static void
main(String args) String
host"truffle" Socket eSocket
null DataoutputStream os null DataInputstr
eam is null DataInputStream stdIn new
DataInpuuStream(System.in)
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Example EchoTest(2)
try eSocket new Socket(host,7) os
new DataOutputStream(eSocket.getOutputStream())
is new DataTnputStream(eSocket.getInp
utStream()) //try catch (UnknownHostExcepti
on e) System.err.println(Unknown host
"host) //catch catch (IOException e)
System.err.println("No I/O connection to
host) ///catch
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Example EchoTest(3)
if (eSocket !null os!null is!null)
try String uTnput while
((uInputstdIn.readLine()) ! null)
os.writeBytes(userlnput) os.writeByte
('\n') System.out.println("echo i
s.readLineo) if (userInput.equals("quit))
break //while os.close() is
.close()
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Example EchoTest(4)
eSocket.close() //try catch
(IOException e) System.err.println("I/O
failed on the connection to host)
//catch //if //try //class
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Example Chat Client(l)
import java.io. import java.net. import
RcveData import SendData public class
chat_client extends Thread public static
void main(String a) throws IOException
Socket sock null String host
localhost" int port 9100
Declaring a Socket object
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Example Chat Client(2)
if (a.length gt 1) port Integer.parseInt(ai
) //if if (a.length gt 0) host
a0 //if System.out.println("using port
port connecting to host) try sock
new Socket(host,port) //try
Establish a connection to the specified bost and
port
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Example Chat Client(3)
catch (java.net.ConnectException e)
System.out.println(e) System.exit(0) //ca
tch SendData sd new SendData(sock) RcveData
rd new RcveData(sock) sd.start() rd.start()
//main //chat_client
Instantiate the supporting classes
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Server Sockets

• A host that responds to a connection.
• Instead of connecting to a remote host, a server
  program will wait for others to connect to it.

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Accepting Connections

• 1) A server socket binds to a particular port.
• 2) It then listens for connection attempts.
• 3) When it detects an attempt, it will accept the
  connection.
• - public Socket accept() Throws IOException
• The accept () method blocks until a connection is
  detected.
• It returns a java. net. Socket Object that is
  used to perform the communication.

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Server Sockets

• Multiple clients can connect to the same port on
  a server at any time.
• The data are distinguished by the port numbers
  and the client addresses.
• However, no more than one socket can listen to a
  particular port at a time.
• This is why servers tend to be heavily
  multithreaded.
• Generally, the server socket listening to the
  port will accept connections and then pass the
  actual processing to other threads.

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Server SocketsQueue

• Incoming connections are stored in a FIFO queue
  until the server can accept them.
• If the queue is full, then connection attempts
  will be refused until space opens up.
• The default queue length for most systems is
  between 5 and 50.

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Server SocketsQueue

• The length of the queue can be adjusted by
  passing in the size of the queue in the backlog"
  parameter.
• - public ServerSocket(int port,int backlog)
• Each system has a maximum queue length, so any
  values for the queue length longer than the
  maximum will be set to the maximum.

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Example Chat Server(l)
//This is a simple chat server written in
Java import java.io. import
java.net. import RcveData import
SendData public class chat_server extends
Thread
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Example Chat Server(2)
public static void main(String a)
int blog 600 int port
9100 Socket sock null if (a.length gt
0) port Integer.parseInt(a0) //if
ServerSocket servsock - null
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Example Chat Server(3)
System.out.println("using port port)
try servsock new Serversocket(port,blog
) // try catch (java.io.IOException e)
System.out.println(e) System.exit(0)
//catch try sock servsock.accept()
//try
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Example Chat Server(4)
catch (java.io.IOException e)
System.out.println(e) System.exit(0)
) //catch SendData Sd new
SendData(sock) RcveData rd new
RcveData(sock) sd.start() rd.start()
//main //class
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Example Send Data(1)
import java.net. import java.io. public
class SendData extends Thread Socket
sock public SendData(Socket sock)
this.sock sock //SendData
constructor public void run() String
line
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Example Send Data(2)
try outputStreamWriter outw
new outputStreamwriter(sock.getOutputStrea
m()) BufferedWriter sockoutnew
BufferedWriter(outw) TnputStreamReader inr
new InputStreamReader(System.in) BufferedRead
er in new BufferedReader(inr) while ((line
in.readLine()) ! null) sockout.write(lin
e"\n")
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Example Send Data(3)
sockout.flush() yield() //whi
le //try catch (java.io.IOException e)
System.out.println(e) System.exit(0)
//catch //run //SendData
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Example Receive Data(1)
import java.net. import java.io. public
class RcveData extends Thread Socket
sock public RcveData(Socket sock)
this.sock sock public void run()
String line
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Example Receive Data(2)
try InputStreamReader inr
new InputStreamReader(sock.getInputStream())
BufferedReader in new BufferedReader(inr)
while (line in.readLine( )) ! null)
System.out.print(Receiving
) System.out.println(line) yield() //
while //try
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Example Receive Data(3)
catch (java.io.IOException e)
system.out.println(e) System.exit(0)
//catch //run //RcveData