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

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

2. 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.

3. Sever - client communication • A socket can be considered as a connection point. port1 portN SEVER: … ... Sockets(Ipc, Port’sM, port1) IP address IPs IP address IPc Socketc(Ips, Port1, port’M) … ... CLIENT: Port’1 Port’M

4. 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.

5. 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.

6. 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()

7. 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( )

8. 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; i<addresses.length;i++) System.out.println(addresses[i]); }//try catch (UnknownHostException e) {} }//main }//class

9. 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

10. 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());

11. Parsing InetAddress byte[] quad = me.getAddress(); for(int i = 0; i < quad.length; i++) System.out.print(quad[i] + ”.”); System.out.println(); }//try catch (UnknownHostException e) { ( System.err.println(e); }//catch }//main }//class

12. 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.

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

14. 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.

15. 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

16. 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.

17. 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

18. 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()

19. 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; DataInputstream is = null; DataInputStream stdIn = new DataInpuuStream(System.in);

20. Example: EchoTest(2) try { eSocket = new Socket(host,7); os = new DataOutputStream(eSocket.getOutputStream()); is = new DataTnputStream(eSocket.getInputStream()); } //try catch (UnknownHostException e) { System.err.println(“Unknown host: "+host); }//catch catch (IOException e) { System.err.println("No I/O connection to: “ + host); }///catch

21. Example: EchoTest(3) if (eSocket !=null && os!=null && is!=null) { try { String uTnput; while ((uInput=stdIn.readLine()) != null) { os.writeBytes(userlnput); os.writeByte('\n'); System.out.println("echo: +is.readLineo); if (userInput.equals("quit”)) break; }//while os.close(); is.close();

22. Example: EchoTest(4) eSocket.close(); }//try catch (IOException e) System.err.println("I/O failed on the connection to: “ + host); }//catch }//if }//try }//class

23. 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

24. Example: Chat Client(2) if (a.length > 1) { port = Integer.parseInt(a[i]); } //if if (a.length > 0) { host = a[0]; }//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

25. Example: Chat Client(3) catch (java.net.ConnectException e){ System.out.println(e); System.exit(0); }//catch SendData sd = new SendData(sock); RcveData rd = new RcveData(sock); sd.start(); rd.start(); }//main }//chat_client Instantiate the supporting classes

26. 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.

27. 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.

28. 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.

29. Server Sockets:Queue • 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.

30. Server Sockets:Queue • 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.

31. 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 {

32. Example: Chat Server(2) public static void main(String a[]) { int blog = 600; int port = 9100; Socket sock = null; if (a.length > 0) { port = Integer.parseInt(a[0]); }//if ServerSocket servsock - null;

33. 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

34. 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

35. 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;

36. Example: Send Data(2) try { outputStreamWriter outw = new outputStreamwriter(sock.getOutputStream()); BufferedWriter sockout=new BufferedWriter(outw); TnputStreamReader inr = new InputStreamReader(System.in); BufferedReader in = new BufferedReader(inr); while ((line = in.readLine()) != null) { sockout.write(line+"\n");

37. Example: Send Data(3) sockout.flush(); yield(); }//while }//try catch (java.io.IOException e) { System.out.println(e); System.exit(0); }//catch }//run }//SendData

38. 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;

39. 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

40. Example: Receive Data(3) catch (java.io.IOException e) { system.out.println(e); System.exit(0); }//catch }//run }//RcveData