Object-Oriented Programming in Java

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1 CSCI/CMPE 3326 Object-Oriented Programming in Java 1. Socket Programming Dongchul Kim Department of Computer Science University of Texas Rio Grande Valley

2 Two types of TCP Socket java.net.serversocket is used by servers so that they can accept incoming TCP/IP connections A server is a piece of software which advertises and then provides some service on request java.net.socket is used by clients who wish to establish a connection to a (remote) server A client is a piece of software (usually on a different machine) which makes use of some service

3 java.net.serversocket (1) Listens on well-known port for incoming connections Creates a dynamically allocated port for each newly established connection Provides a Socket connected to the new port Maintains a queue to ensure that prospective clients are not lost

4 java.net.serversocket (2) Construction: ServerSocket(int port, int backlog) Allows up to backlog requests to queue waiting for the server to deal with them Some useful methods: Socket accept() Blocks waiting for a client to attempt to establish a connection void close() Called by the server when it is shutting down to ensure that any resources are deallocated

5 java.net.socket (1) Provides access to TCP/IP streams Bi-directional communication between sender and receiver Can be used to connect to a remote address and port by using the constructor: Socket(String remotehost, int port) Also used to accept an incoming connection (see ServerSocket)

6 java.net.socket (2) Can obtain access to input and output streams Input stream allows reception of data from the other party InputSteam getinputstream() Output stream allows dispatch of data to the other party OutputStream getoutputstream()

7 How it all fits together Client (sid) s = new Socket ( fred, 80) Server (fred) ServerSocket ss. s = ss.accept() Socket s s.getinputstream() s.getouputstream() s.getinputstream() s.getouputstream()

8 A sample TCP server public static void main(string[] args) throws IOException { ServerSocket listener = new ServerSocket(9090); try { while (true) { Socket socket = listener.accept(); try { PrintWriter out = new PrintWriter(socket.getOutputStream(), tru out.println("hello"); finally { socket.close(); finally { listener.close();

9 A sample TCP client public class Client { public static void main(string[] args) throws IOException { String serveraddress = JOptionPane.showInputDialog( "Enter IP Address of a machine that is\n" + "running the date service on port 9090:"); Socket s = new Socket(serverAddress, 9090); BufferedReader input = new BufferedReader(new InputStreamReader(s.getInputStream())); String answer = input.readline(); JOptionPane.showMessageDialog(null, answer); s.close(); System.exit(0);

10 CSCI/CMPE 3326 Object-Oriented Programming in Java Lab15 Dongchul Kim Department of Computer Science University of Texas Rio Grande Valley

11 import java.io.*; import java.net.*; Server public class Server { public static void main(string[] args) throws IOException { ServerSocket ss = new ServerSocket(9090); ss.setsotimeout(100000); while(true) { try { System.out.println("Waiting for client on port " +ss.getlocalport() + "..."); Socket server = ss.accept(); System.out.println("Just connected to " + server.getremotesocketaddress()); DataInputStream in = new DataInputStream(server.getInputStream()); // message from client System.out.println(in.readUTF()); DataOutputStream out = new DataOutputStream(server.getOutputStream()); // message to client out.writeutf("thank you for connecting to Dr. Kim s server " + server.getlocalsocketaddress() +". Goodbye!"); server.close(); catch(sockettimeoutexception s) { System.out.println("Socket timed out!"); break; catch(ioexception e) { e.printstacktrace(); break; ss.close();

12 import java.io.*; import java.net.*; public class Client { Client public static void main(string[] args) throws IOException { String servername = localhost"; int port = 9090; try { System.out.println("Connecting to " + servername + " on port " + port); Socket client = new Socket(serverName, port); System.out.println("Just connected to " + client.getremotesocketaddress()); DataOutputStream out = new DataOutputStream(client.getOutputStream()); // message to server out.writeutf("hello from Dr. Kim s client " + client.getlocalsocketaddress()); DataInputStream in = new DataInputStream(client.getInputStream()); // message from server System.out.println("Server says " + in.readutf()); client.close(); catch(ioexception e) { e.printstacktrace();

13 Lab assignment Make a java socket program to communicate with server and client using the reference codes above. You should use port number Run your server firstly. Try to make a connection from your client program to any classmate s server. TA will go around and check your lab.

14 Submission Please give a demo to your instructor or TA

JAVA - NETWORKING (SOCKET PROGRAMMING)

JAVA - NETWORKING (SOCKET PROGRAMMING) http://www.tutorialspoint.com/java/java_networking.htm Copyright tutorialspoint.com The term network programming refers to writing programs that execute across multiple