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Java networking programs socket based


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java networking programs - socket based

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Java networking programs socket based

  1. 1. Java – Networking Page 1 Java – Networking PROGRAMSProgram 1: Write a program that obtains the IP address of a site./* Program to find the IP address of a website */// Mukesh N Tekwaniimport*;import*;class AddressDemo{ public static void main(String args[]) throws IOException { BufferedReader br = new BufferedReader(new InputStreamReader(; System.out.print("Enter a website name: "); String site = br.readLine(); try { InetAddress ip = InetAddress.getByName(site); System.out.print("The IP address is: " + ip); } catch(UnknownHostException e) { System.out.println("WebSite not found"); } }}/* Output:C:JavaPrgs>java AddressDemoEnter a website name: IP address is:*/Modification:Modify the above program so that it takes the website name (e.g., from thecommand line. If the website address is not given at command line, use the default address [Mobile:9869 488 356] Prof. Mukesh N. Tekwani
  2. 2. 2 Java - NetworkingProgram 2: Write a program that connects to the home page of (readfrom a URL).//Program to connect to the home page of Mukesh N Tekwaniimport*;import*;public class URLReader{ public static void main(String[] args) throws Exception { URL myurl = new URL(""); BufferedReader in = new BufferedReader(new InputStreamReader(myurl.openStream())); String inputLine; while ((inputLine = in.readLine()) != null) System.out.println(inputLine); in.close(); }}Output:When this program is run, it displays the complete HTML code of the web page.Possible Error: If we give site address simply as, we get MalformedURLException.The protocol http must also be given in the complete URL.Modification:Modify the above program so that it takes the website name (e.g., from thecommand line. If the website address is not given at command line, use the default address Mukesh N Tekwani [Mobile:9869 488 356]
  3. 3. Java - Networking Page 3Program 3: Write a program that parses a URL address into its components.//Program to parse a URL address into its components// Mukesh N Tekwaniimport*;import*;public class ParseAddress{ public static void main (String[] args) { if (args.length !=1) { System.out.println ("Error: missing url argument"); System.out.println ("Usage: java ParseURL <url>"); System.exit (0); } try { URL siteurl = new URL (args[0]); System.out.println ("Protocol = " + siteurl.getProtocol ()); System.out.println("Host = " + siteurl.getHost ()); System.out.println("File name= " + siteurl.getFile()); System.out.println("Port = " + siteurl.getPort ()); System.out.println("Target = " + siteurl.getRef ()); } catch (MalformedURLException e) { System.out.println ("Bad URL = " + args[0]); } } // main} // class ParseAddressOutput:C:JavaPrgs>java ParseAddress = httpHost = name =Port = -1Target = [Mobile:9869 488 356] Prof. Mukesh N. Tekwani
  4. 4. 4 Java - NetworkingProgram 4: Write a program to translate an IP address into host name or a host name toan IP address.// Translate IP address to hostname or vice-versa// Mukesh N Tekwaniimport*;import*;class TranslateAddress{ public static void main (String args[]) { if (args.length != 1) { System.out.println ("Error! No IP or host name address"); System.out.println ("Usage: java TranslateAddress"); System.out.println (" or java TranslateAddress"); System.exit (0); } try { // When the argument passed is a host name(e.g. //, the corresponding IP address is returned. // If passed an IP address, then only the IP address // is returned. InetAddress ipadd = InetAddress.getByName (args[0]); System.out.println ("Address " + args[0] + " = " + ipadd); // To get the hostname when passed an IP address use // getHostName (), which will return the host name // string. System.out.println ("Name of " + args[0] + " = " + ipadd.getHostName ()); } catch (UnknownHostException e) { System.out.println ("Unable to translate the address."); } } // main } // class TranslateAddress/* Output:C:JavaPrgs>java TranslateAddress = / of =*/Prof. Mukesh N Tekwani [Mobile:9869 488 356]
  5. 5. Java - Networking Page 5Program 5: Write a program to print all the addresses of Get all IP addresses by name of site// Mukesh N Tekwaniimport*;public class AllAddressesOfMicrosoft{ public static void main (String[] args) { try { InetAddress[] ipadd = InetAddress.getAllByName(""); for (int i = 0; i < ipadd.length; i++) { System.out.println(ipadd[i]); } } catch (UnknownHostException ex) { System.out.println("Could not find"); } }}/*Output:C:JavaPrgs>java*/Modification: Write a program that prints the Internet Address of the local host if we do notspecify any command-line parameters or all Internet addresses of another host if we specify the hostname on the command [Mobile:9869 488 356] Prof. Mukesh N. Tekwani
  6. 6. 6 Java - NetworkingProgram 6: Write a program to obtain the IP address of the local machine.// Find the IP address of the local machine// Mukesh n Tekwaniimport*;public class MyOwnAddress{ public static void main (String[] args) { try { InetAddress me = InetAddress.getLocalHost(); String myadd = me.getHostAddress(); System.out.println("My address is " + myadd); } catch (UnknownHostException e) { System.out.println("Im sorry. I dont know my own address; really lost!!!."); } }}/* Output:C:JavaPrgs>java MyOwnAddressMy address is*/Prof. Mukesh N Tekwani [Mobile:9869 488 356]
  7. 7. Java - Networking Page 7Program 7: Write a program that accepts an IP address and finds the host name.// Given the IP address, find the host name// Mukesh N Tekwaniimport*;public class ReverseTest{ public static void main (String[] args) { try { InetAddress ia = InetAddress.getByName(""); System.out.println(ia.getHostName()); System.out.println(ia); } catch (Exception e) { System.out.println(e); } }}/* Output:C:JavaPrgs>java*/ [Mobile:9869 488 356] Prof. Mukesh N. Tekwani
  8. 8. 8 Java - NetworkingProgram 8: Write a program to download a file from the Internet and either copy it as afile on the local machine or display it on the screen.// Program-download a file & copy it as a file or display it on screen// Mukesh N Tekwaniimport*;import*;public class DownLoadFile{ public static void main(String args[]) { InputStream in = null; OutputStream out = null; try { if ((args.length != 1) && (args.length != 2)) throw new IllegalArgumentException("Wrong no. of arguments"); URL siteurl = new URL(args[0]); in = siteurl.openStream(); if(args.length == 2) out = new FileOutputStream(args[1]); else out = System.out; //display on client machine byte [] buffer = new byte[4096]; int bytes_read; while((bytes_read = != -1) out.write(buffer, 0, bytes_read); } catch (Exception ex) { System.out.println(ex); } finally { try { in.close(); out.close(); } catch (Exception ae) { System.out.println(ae); } } }}/* Output:C:JavaPrgs>java DownLoadFile test.txt*/Prof. Mukesh N Tekwani [Mobile:9869 488 356]
  9. 9. Java - Networking Page 9 CLIENT-SERVER PROGRAMS (Using Sockets) Client Server Create TCP Socket Create TCP Socket Socket cs = new ServerSocket ss = new Socket(hostname, port); ServerSocket(port); Client initiates the communication Wait for client connection by reading the user input Socket listen_socket = Str = ss.accept(); userinput.readLine(); Then reads the client on listen_socket. Then sends it to server Server listens client Server_out.writeBytes(str client_str = + ‘n’); client_input.readLine(); Client listens to server using client Server sends reply to client socket Close client [Mobile:9869 488 356] Prof. Mukesh N. Tekwani
  10. 10. 10 Java - Networking Program 9: Write a client/server program in which a client sends a single string to the server. The server just displays this string. (Echo) Server Program: //Server Program //Works with file Client1 //Mukesh N Tekwani import*; import*; class Server1 { public static void main(String args[]) throws Exception { //create server socket ServerSocket ss = new ServerSocket(4444); while (true) { Socket listen_socket = ss.accept(); BufferedReader client_input = new BufferedReader(new InputStreamReader(listen_socket.getInputStream())); String client_str; //to store string rcvd from client client_str = client_input.readLine(); System.out.println(client_str); } } } Client Program: //Client Program //Works with file Server1 //Mukesh N Tekwani import*; import*; class Client1 { public static void main(String args[]) throws Exception { //create client socket Socket cs = new Socket("localhost", 4444); BufferedReader user_input = new BufferedReader(new InputStreamReader(; DataOutputStream server_out = new DataOutputStream(cs.getOutputStream()); Prof. Mukesh N Tekwani [Mobile:9869 488 356]
  11. 11. Java - Networking Page 11 String str; str = user_input.readLine(); server_out.writeBytes(str + n); cs.close(); }}Program : Write a TCP/IP client / server program that sends a string in lowercase to theserver which sends the equivalent uppercase string back to the client.Server Program://The server code*;import*;public class ServerLower{ // the socket used by the server private ServerSocket serverSocket; ServerLower(int port) // server constructor { /* create socket server and wait for connection requests */ try { serverSocket = new ServerSocket(port); System.out.println("Server waiting for client on port " + serverSocket.getLocalPort()); while(true) { Socket socket = serverSocket.accept(); System.out.println("New client asked for a connection"); TcpThread t = new TcpThread(socket); System.out.println("Starting a thread for a new Client"); t.start(); } } catch (IOException e) { System.out.println("Exception on new ServerSocket:" + e); } } public static void main(String[] arg) { new ServerLower(4444); } [Mobile:9869 488 356] Prof. Mukesh N. Tekwani
  12. 12. 12 Java - Networking /** One instance of this thread will run for each client */ class TcpThread extends Thread { Socket socket; // the socket where to listen/talk ObjectInputStream Sinput; ObjectOutputStream Soutput; TcpThread(Socket socket) { this.socket = socket; } public void run() { /* Creating both Data Streams */ System.out.println("Thread trying to create Object Input/Output Streams"); try { // create output first Soutput = new ObjectOutputStream(socket.getOutputStream()); Soutput.flush(); Sinput = new ObjectInputStream(socket.getInputStream()); } catch (IOException e) { System.out.println("Exception creating new Input/output Streams: " + e); return; } System.out.println("Thread waiting for a String from the Client"); // read a String (which is an object) try { String str = (String) Sinput.readObject(); str = str.toUpperCase(); //convert lower 2 uppercase Soutput.writeObject(str); Soutput.flush(); } catch (IOException e) { System.out.println("Exception reading/writing Streams: " + e); return; } catch (ClassNotFoundException e1) { //nothing needed here } finally Prof. Mukesh N Tekwani [Mobile:9869 488 356]
  13. 13. Java - Networking Page 13 { try { Soutput.close(); Sinput.close(); } catch (Exception e2) { //nothing needed here } } } }}Client Program://The client code that sends a string in lowercase to the serverimport*;import*;public class ClientLower{ ObjectInputStream Sinput; // to read the socker ObjectOutputStream Soutput; // towrite on the socket Socket socket; // Constructor connection receiving a socket number ClientLower(int port) { try { socket = new Socket("localhost", port); } catch(Exception e) { System.out.println("Error connectiong to server:" + e); return; } System.out.println("Connection accepted " + socket.getInetAddress() + ":" + socket.getPort()); /* Creating both Data Streams */ try { Sinput = new ObjectInputStream(socket.getInputStream()); Soutput = new ObjectOutputStream(socket.getOutputStream()); } catch (IOException e) { System.out.println("Exception creating I/O Streams:"+ e); return; } [Mobile:9869 488 356] Prof. Mukesh N. Tekwani
  14. 14. 14 Java - Networking String test = "aBcDeFgHiJkLmNoPqRsTuVwXyZ"; // send the string to the server System.out.println("Client sending "" + test + "" to server"); try { Soutput.writeObject(test); Soutput.flush(); } catch(IOException e) { System.out.println("Error writting to the socket: " + e); return; } // read back the answer from the server String response; try { response = (String) Sinput.readObject(); System.out.println("Read back from server: " + response); } catch(Exception e) { System.out.println("Problem reading back from server: " + e); } try { Sinput.close(); Soutput.close(); } catch(Exception e) { // nothing needed here } } public static void main(String[] arg) { new ClientLower(4444); } } Modifications: 1. Modify the Server program in this example so that it is not multithreaded. 2. Modify the client program so that the input string is entered by the user from keyboard when program runs, instead of storing it within the program. Prof. Mukesh N Tekwani [Mobile:9869 488 356]
  15. 15. Java - Networking Page 15Program 17:Write a client-server socket application in which(i) A client reads a character from the keyboard and sends the character out of its socket to the server.(ii) The server reads the character from its connection socket(iii) The server finds the ASCII value of the character.(iv) The server sends the ASCII value out of its connection socket to the client.(v) The client reads the result from its socket and prints the result on its standard output device.Server Program://Server sends the ASCII code of a character to client//Mukesh N Tekwaniimport*;import*;class ServerASCII{ public static void main(String args[]) throws Exception { String clientstr, serverstr; ServerSocket ss = new ServerSocket(4444); while(true) { Socket cs = ss.accept(); System.out.println("Connected to client..."); BufferedReader inFromClient = new BufferedReader(new InputStreamReader(cs.getInputStream())); DataOutputStream outToClient = new DataOutputStream(cs.getOutputStream()); clientstr = inFromClient.readLine(); //read the first character from input char c = clientstr.charAt(0); /* Find the ASCII code; note the type casting */ serverstr = "The ASCII code of " + clientstr + " is " + (int)c + n; outToClient.writeBytes(serverstr); } }}Output at Client end:C:JavaPrgs>java ClientASCIIEnter a characterBFrom server: The ASCII code of B is [Mobile:9869 488 356] Prof. Mukesh N. Tekwani
  16. 16. 16 Java - Networking PORTS AND SOCKETS Understanding Ports Generally speaking, a computer has a single physical connection to the network. All data destined for a particular computer arrives through that connection. However, the data may be intended for different applications running on the computer. So how does the computer know to which application to forward the data? Through the use of ports. Data transmitted over the Internet is accompanied by addressing information that identifies the computer and the port for which it is destined. The computer is identified by its 32-bit IP address, which IP uses to deliver data to the right computer on the network. Ports are identified by a 16-bit number, which TCP and UDP use to deliver the data to the right application. In connection-based communication such as TCP, a server application binds a socket to a specific port number. This has the effect of registering the server with the system to receive all data destined for that port. A client can then rendezvous with the server at the servers port, as illustrated here: Definition: The TCP and UDP protocols use ports to map incoming data to a particular process running on a computer. In datagram-based communication such as UDP, the datagram packet contains the port number of its destination and UDP routes the packet to the appropriate application, as illustrated in this figure: Port numbers range from 0 to 65,535 because ports are represented by 16-bit numbers. The port numbers ranging from 0 - 1023 are restricted; they are reserved for use by well-known services such as HTTP and FTP and other system services. These ports are called well-known ports. Your applications should not attempt to bind to them. Understanding Sockets In client-server applications, the server provides some service, such as processing database queries or sending out current stock prices. The client uses the service provided by the server, either displaying database query results to the user or making stock purchase recommendations to an investor. The communication that occurs between the client and the server must be reliable. That is, no data can be dropped and it must arrive on the client side in the same order in which the server sent it. Prof. Mukesh N Tekwani [Mobile:9869 488 356]
  17. 17. Java - Networking Page 17TCP provides a reliable, point-to-point communication channel that client-server applications on the Internetuse to communicate with each other. To communicate over TCP, a client program and a server programestablish a connection to one another. Each program binds a socket to its end of the connection. Tocommunicate, the client and the server each reads from and writes to the socket bound to the connection.What Is a Socket?A socket is one end-point of a two-way communication link between two programs running on the network.Socket classes are used to represent the connection between a client program and a server program. package provides two classes--Socket and ServerSocket--that implement the client side of theconnection and the server side of the connection, [Mobile:9869 488 356] Prof. Mukesh N. Tekwani