Router simulation

gistfile1.java

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Inet4Address;
import org.apache.commons.net.util.SubnetUtils;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class Router {
    private Map<String, String> interfaces;
    private Set<Route> routingTable;
    private Route defaultRoute;

    public Router() {
        interfaces = new HashMap<>();
        routingTable = new HashSet<>();
    }

    public static void main(String[] args) {
        Router router = new Router();
        if (args.length < 2) {
            System.out.println("No arguments supplied!");
            return;
        }
        File routesFile = new File(args[0]);
        File packetsFile = new File(args[1]);
        if (!routesFile.exists()) {
            System.out.println("Routing table file not found!");
        }
        if (!packetsFile.exists()) {
            System.out.println("Routing table file not found!");
        }

        try {
            router.parseRoutingFile(routesFile);
            System.out.println("Added " + router.routingTable.size() + " routes from config");
        } catch (IOException e) {
            System.out.println("Routing table file has invalid format! " + e.getMessage());
            e.printStackTrace();
            return;
        }

        try {
            router.parsePacketsFile(packetsFile);
        } catch (IOException e) {
            System.out.println("Packets file has invalid format! " + e.getMessage());
            e.printStackTrace();
            return;
        }
    }


    public void parseRoutingFile(File file) throws IOException {
        BufferedReader buf = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
        String line;
        while ((line = buf.readLine()) != null) {
            String[] strLine = line.trim().split("//");
            String destination = strLine[0].trim().substring(5);
            String netmask = strLine[1].trim().substring(5);
            String gateway = strLine[2].trim().substring(4);
            String iface = strLine[3].trim().substring(4);
            int metric = Integer.parseInt(strLine[4].trim().substring(5));

            SubnetUtils subnet = new SubnetUtils(destination, netmask);
            Inet4Address ifce = (Inet4Address) Inet4Address.getByName(iface);
            Route route = new Route(subnet.getInfo(), (Inet4Address) Inet4Address.getByName(gateway), ifce, metric);
            if (destination.equals("0.0.0.0")) defaultRoute = route;
            if (!interfaces.keySet().contains(ifce.getHostAddress())) interfaces.put(ifce.getHostAddress(), "eth" + interfaces.size());
            routingTable.add(route);
        }
        buf.close();
    }

    public void parsePacketsFile(File file) throws IOException {
        BufferedReader buf = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
        String line;
        while ((line = buf.readLine()) != null) {
            String[] strLine = line.trim().split(":");
            String dest = strLine[1].trim();
            Route bestRoute = null;
            int bestMetric = -1;
            routingTable.remove(defaultRoute);
            for (Route route : routingTable) {
                // CHECK IF DESTINATION BELONGS TO THIS ROUTE
                if (route.network.isInRange(dest)) {
                    // CHECK METRICS
                    if (bestMetric == -1 || bestMetric > route.metric) {
                        bestMetric = route.metric;
                        bestRoute = route;
                    }
                }
            }
            if (bestRoute == null) {
                bestRoute = defaultRoute;
            }
            System.out.println("Packet with destination " + dest + " will be forwarded to " + bestRoute.gateway.getHostAddress() + " on interface " + interfaces.get(bestRoute.iface.getHostAddress()));
        }
        buf.close();
    }


    private class Route {
        final SubnetUtils.SubnetInfo network;
        final Inet4Address gateway;
        final Inet4Address iface;
        final int metric;

        public Route(SubnetUtils.SubnetInfo subnet, Inet4Address gateway, Inet4Address address, int metric) {
            this.network = subnet;
            this.gateway = gateway;
            this.iface = address;
            this.metric = metric;
        }
    }

}