topology.java

使用Java语言编写模拟路由器程序

/* File: Topology.java
 *
 * This file contains the code for the class Topology
 * which represents the initial topology of the network of routers
 * 
 * This object is built from the Topology Configuration File
 * Each Router uses this object to learn about its initial neighbors
 * and constructs the initial routing table.
 */

import java.util.*;
import java.util.regex.*;
import java.io.*;

class Topology {
	// The topology is represented by a list of entries,
	// each entry representing an edge/link in the network
	LinkedList entries;

	/*
	 * Constructor
	 * 
	 * Use: To read the Topology Configuration File and construct the object
	 * 
	 * @filename: the name of the Topology Configuration File
	 */
	public Topology(String filename) {
		entries = new LinkedList();

		BufferedReader in = null;

		// open the file for reading
		try {
			in = new BufferedReader(new FileReader(filename));
		} catch (IOException e) {
			System.out.println("Unable to open file: " + filename);
			System.out.println("Quitting.");

			System.exit(1);
		}

		try {
			String[] fields;
			String line;

			int router1 = -1;
			int router2 = -1;
			int weight = -1;

			int linenumber = 1;

			// read a line
			line = in.readLine();

			while (line != null) {
				if (line.equals("") != true) {

					try {
						// split the entry using "," as a delimiter
						fields = line.split(",");

						if (fields.length != 3) {
							System.out.println("Line " + linenumber
									+ " in file " + filename
									+ " : Invalid entry");
							System.out.println("Quitting.");

							System.exit(1);
						}

						// get the individual elements - origin and destination
						// nodes, and the weight
						router1 = Integer.parseInt(fields[0]);
						router2 = Integer.parseInt(fields[1]);
						weight = Integer.parseInt(fields[2]);
					}

					catch (PatternSyntaxException pse) {
						System.out
								.println("Pattern Syntax Exception in RouterLocation.java");
						System.out.println("Quitting.");

						System.exit(1);
					}

					// invalid entry in the file
					catch (NumberFormatException nfe) {
						System.out.println("Line number " + linenumber
								+ " in file " + filename + ": Invalid number");
						System.out.println("Quitting.");

						System.exit(1);
					}

					// add an entry to the listcorresponding to this edge
					entries
							.add(new TopologyFileEntry(router1, router2, weight));
				}
				linenumber++;

				line = in.readLine();
			}

			in.close();
		} catch (IOException ioe) {
			System.out
					.println("I/O error occured while reading from the file: "
							+ filename);
			System.out.println("Quitting.");

			System.exit(1);
		}

		return;
	}

	/*
	 * Method Name: getRouterIds
	 * 
	 * Use: To get the list of router ids in the initial topology
	 */
	HashSet getRouterIds() {
		HashSet h = new HashSet();

		Iterator i = entries.iterator();

		while (i.hasNext()) {
			h.add(new Integer(((TopologyFileEntry) i.next()).getRouter1()));
		}

		return h;
	}

	/*
	 * Method Name: getEntries
	 * 
	 * Use: to get the entries in the Topology Configuration File
	 */
	LinkedList getEntries() {
		return entries;
	}

}