magpie:network/> cat -n Server.java
     1	// This example is from the book _Java in a Nutshell_ by David Flanagan.
     2	// Written by David Flanagan.  Copyright (c) 1996 O'Reilly & Associates.
     3	// You may study, use, modify, and distribute this example for any purpose.
     4	// This example is provided WITHOUT WARRANTY either expressed or implied.
     5	// Modified by tsaiwn@csie.nctu.edu.tw with BufferedReader to read data
     6	// .. plus, handling EOF / disconnection request
     7	
     8	import java.io.*;
     9	import java.net.*;
    10	public class Server extends Thread {
    11	    public final static int DEFAULT_PORT = 6789;
    12	    protected int port;
    13	    protected ServerSocket listen_socket;
    14	    
    15	    // Exit with an error message, when an exception occurs.
    16	    public static void fail(Exception e, String msg) {
    17	        System.err.println(msg + ": " +  e );
    18	        System.exit(1);
    19	    }
    20	    
    21	    // Create a ServerSocket to listen for connections on;  start the thread.
    22	    public Server(int port) {  // constructor
    23	        if (port == 0) port = DEFAULT_PORT;
    24	        this.port = port;
    25	        try { listen_socket = new ServerSocket(port); }
    26	        catch (IOException e) { 
    27		    fail(e, "Exception creating server socket");
    28		}
    29	        System.out.println("Server: listening on port " + port);
    30	        this.start();
    31	    } // Server constructor
    32	    
    33	    // The body of the server thread.  Loop forever, listening for and
    34	    // accepting connections from clients.  For each connection, 
    35	    // create a Connection object to handle communication through the
    36	    // new Socket.
    37	    public void run() {
    38	        try {
    39	            while(true) {  // accept( ) will wait someone to connect me
    40	                Socket client_socket = listen_socket.accept();
    41	                Connection c = new Connection(client_socket);  // thread
    42	            } // while(true); Loop forever to serve clients
    43	        }
    44	        catch (IOException e) { 
    45	            fail(e, "Exception while listening for connections");
    46	        }
    47	    } // run
    48	    
    49	    // Start the server up, listening on an optionally specified port
    50	    public static void main(String[ ] args) {
    51	        int port = 0;
    52	        if (args.length == 1) {
    53	            try { port = Integer.parseInt(args[0]);  }
    54	            catch (NumberFormatException e) { port = 0; }
    55	        }
    56	        new Server(port);
    57	    } // main
    58	} // class Server ends here
    59	
    60	// This class is the thread that handles all communication with a client
    61	class Connection extends Thread {
    62	    protected Socket client;
    63	    protected DataInputStream dis;
    64	    protected InputStreamReader isr;
    65	    protected BufferedReader in;
    66	    protected PrintStream out;
    67	    protected InetAddress who;   // Client IP_address
    68	    protected String name;   // Client Host_Name
    69	    
    70	    // Initialize the streams and start the thread
    71	    public Connection(Socket client_socket) {   // constructor
    72	        client = client_socket;
    73	        who = client.getInetAddress( );  // by tsaiwn
    74	        name = " " + who.getHostName( );
    75	        java.util.Date now = new java.util.Date( );
    76	        System.err.println(""+who+name+" entered at " + now);  // by tsaiwn
    77	        try { 
    78	            dis = new DataInputStream(client.getInputStream());
    79	            isr = new InputStreamReader(dis);
    80	            in  = new BufferedReader(isr);   // by tsaiwn@csie.nctu.edu.tw
    81	            out = new PrintStream(client.getOutputStream());
    82	        }
    83	        catch (IOException e) {
    84	            try { client.close(); } catch (IOException e2) { ; }
    85	            System.err.println("Exception while getting socket streams: " + e);
    86	            return;
    87	        }
    88	        this.start();
    89	    } // Connection constructor
    90	        
    91	    // Provide the service.
    92	    // Read a line, reverse it, send it back.
    93	    public void run() {
    94	        String line;
    95	        StringBuffer revline;
    96	        int len;
    97	        try {
    98	            for(;;) {  // loop forever
    99	                // read in a line
   100	                try {
   101	                   line = in.readLine();
   102	                } catch (EOFException e) { line = null; }
   103	                if (line == null) break;
   104	                System.err.println(""+line.length()+" "+line); // tsaiwn
   105	                // reverse it
   106	                len = line.length();
   107	      if(len==1) if( (int)(line.charAt(0)) == 3 )  break;  // CTRL_C
   108	      if(len==1) if( (int)(line.charAt(0)) == 26 )  break;  // CTRL_Z
   109	                revline = new StringBuffer(len);
   110	                for(int i = len-1; i >= 0; i--) 
   111	                    revline.insert(len-1-i, line.charAt(i));
   112	                // and write out the reversed line
   113	                out.println(revline);
   114	            }
   115	        } catch (IOException e) { ; }
   116	        finally { try {client.close();} catch (IOException e2) {;}
   117	           java.util.Date now = new java.util.Date( );
   118	           System.err.println(""+who+name+" leaving at " + now);
   119	        }
   120	    } // run
   121	} // class Connection
   122