tcpechoserver.java

this gives details of the network programming

// Sample Java Program
// TCP Echo Server
//
// Based partially on the code in TCP/IP Sockets in Java, by Calvert and Donahoo
//
// Requires a single command line arg - the port number


import java.net.*;	// need this for InetAddress, Socket, ServerSocket
import java.io.*;	// need this for I/O stuff 

public class TCPEchoServer {

    // define a constant used as size of buffer
    static final int BUFSIZE=1024;

    // main starts things rolling

    static public void main(String args[]) {
	if (args.length != 1) {
	    throw new IllegalArgumentException("Must specify a port!");
	}

	int port = Integer.parseInt(args[0]);

	try {
	    // Create Server Socket (passive socket)
	    ServerSocket ss = new ServerSocket(port);

	    while (true) {
		Socket s = ss.accept();
		handleClient(s);
	    }
	} catch (IOException e) {
	    System.out.println("Fatal I/O Error !");
 	    System.exit(0);
	}

    }

    // this method handles one client
    // declared as throwing IOException - this means it throws 
    // up to the calling method (who must handle it!)

    // try taking out the "throws IOException" and compiling,
    // the compiler will tell us we need to deal with this!

    static void handleClient(Socket s) throws IOException {
	byte[] buff = new byte[BUFSIZE];
	int bytesread = 0;

	// print out client's address
	System.out.println("Connection from " + s.getInetAddress().getHostAddress());

	// Set up streams
	InputStream in = s.getInputStream();
	OutputStream out = s.getOutputStream();

	// read/write loop
	while ((bytesread = in.read(buff)) != -1) {
	    out.write(buff,0,bytesread);
	}
	s.close();
    }
}