TcpExample4HandlerThread.java

package TcpExamples;

import java.io.*;
import java.net.*;

/**
 * A program that handles all logic associated with one socket connection
 * by running in a thread of its own. This is the server
 * portion as well, so we artificially invent what happens
 * if the server can't respond to a connection for several seconds.
 * Warning: do not run this class!  It is created automatically by TcpExample4DispatchServer.
 * 
 * @author Don McGregor
 * @author Don Brutzman
 * @author MV3500 class
 */
class TcpExample4HandlerThread extends Thread
{
    /** The socket connection to a client */
    Socket socket;
    
    /** The thread constructor creates the socket from
     * a ServerSocket, and passes one to the thread
     * responsible for handling the connection.
     * 
     * @param socket The socket connection handled by this thread
     */
    TcpExample4HandlerThread(Socket socket)
    {
        this.socket = socket;
    }
    
    /** Handles one connection. We add an artificial slowness
     * to handling the connection with a sleep(). This means
     * the client won't see a server connection response for ten seconds (default).
     */
    // @overriding run() method in Java Thread class is deliberate
    @Override 
    public void run()
    {
        try
        {
            System.out.println(TcpExample4HandlerThread.class.getName() + " starting to handle a thread...");
            
            // get the connection output stream, then wait a period of time. 
            OutputStream os = socket.getOutputStream();
            PrintStream ps = new PrintStream(os);

            final long TIMEOUT = 2000; // 2000 milliseconds = 2 seconds, 10000 milliseconds = 10 seconds
            System.out.println(TcpExample4HandlerThread.class.getName() + " pausing for TIMEOUT=" + TIMEOUT + "ms" + 
                               " to emulate computation and avoid server-side overload"); 
            Thread.sleep(TIMEOUT);
                
            // ps is the PrintStream is the Java way to use System.print() to pass data along the socket.
            ps.println("This message was written by the server " + TcpExample4HandlerThread.class.getName()); // TODO insert socket count here!
            ps.flush();     // make sure that it indeed escapes current process and reaches the client
            socket.close(); // all clear, no longer need socket
            System.out.println(TcpExample4HandlerThread.class.getName() + " finished handling a thread, now exit.");
        }
        catch(IOException | InterruptedException e) // either a networking or a threading problem
        {
            System.out.println("Problem with " + TcpExample4HandlerThread.class.getName() + " networking:"); // describe what is happening
            System.out.println("Error: " + e);
            
            // Provide more helpful information to user if exception occurs due to running twice at one time
            if (e instanceof java.net.BindException)
                System.out.println("*** Be sure to stop any other running instances of programs using this port!");
        }
    }
}