commandthread.java

使用Java语言编写模拟路由器程序

/* File: CommandThread.java
 *
 * Author: Venkata Sastry Malladi
 *
 * This file contains the code for the class CommandThread,
 * which represents the thread spawned by each Router to 
 * listen for commands sent by the Command
 *
 * Preferred Editor: emacs
 */
import java.io.*;
import java.net.*;

class CommandThread extends Thread {
	// the instance of the router that spawned this thread
	Router r;

	// the port on which the thread listens for commands from the Command
	// program
	int port;

	/*
	 * Constructor
	 * 
	 * @r: the instance of the router that spawned this thread @port: port
	 * number
	 */
	public CommandThread(Router r, int port,String threadName) {
		// create the thread
		super(threadName);

		this.r = r;
		this.port = port;

		// start the thread;
		start();
	}

	/*
	 * Method Name: run
	 * 
	 * Use: To start the execution of the thread
	 */
	public void run() {
		// socket to listen on the command port
		ServerSocket l = null;

		// socket to represent the accepted connection
		Socket t;

		// the input and output streams associated with the connection
		ObjectOutputStream oos;
		ObjectInputStream ois;

		try {
			// listen on the command port
			l = new ServerSocket(port);
			System.out.println("Router "+Thread.currentThread().getName()+" Command: Listening for commands on port "
					+ port);
		} catch (Exception e) {
			System.out
					.println("Router "+Thread.currentThread().getName()+" Command: Unable to open a listening socket on port: "
							+ port);
			System.out.println("Quitting.");
			System.exit(1);
		}

		while (true) {
			try {
				// accept a connection
				t = l.accept();
			} catch (Exception e) {
				System.out
						.println("Router "+Thread.currentThread().getName()+" Command: An I/O error occured while accepting a connection");
				continue;
			}

			try {
				// open the streams
				oos = new ObjectOutputStream(t.getOutputStream());
				ois = new ObjectInputStream(t.getInputStream());

				// read the command
				String in = (String) ois.readObject();

				// execute the command and send the response
				String out = r.executeCommand(in);
				oos.writeObject(out);

				// close the streams and the connection
				ois.close();
				oos.close();
				t.close();
			} catch (Exception e) {
				System.out
						.println("Router "+Thread.currentThread().getName()+" Command: An I/O error occured while communicating with COMMAND");
				continue;
			}
		}
	}
}