Java Local Address Get getLocalAddress()

Description

The preferred local address.

License

Apache License

Return

The local address to use.

Declaration

public static InetAddress getLocalAddress() 

Method Source Code

//package com.java2s;
/**/* w ww  .  ja va  2s  .co  m*/
 * Appia: Group communication and protocol composition framework library
 * Copyright 2006 University of Lisbon
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License. 
 *
 * Initial developer(s): Alexandre Pinto and Hugo Miranda.
 * Contributor(s): See Appia web page for a list of contributors.
 */

import java.io.PrintStream;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Enumeration;

public class Main {
    public static final PrintStream debug = null;

    /**
     * The preferred local address.
     * <br>
     * It chooses from the existing local address the one that satisfies more of the following rules, 
     * applying the rules by the order presented:
     * <nl>
     * <li> Is IPv4 address;
     * <li> Isn't a Local Link address;
     * <li> Isn't a Loopback address;
     * <li> Isn't a Site Local address;
     * <li> Has the lower interface number;
     * <li> Has the lower interface name.
     * </nl>
     * 
     * @return The local address to use.
     */
    public static InetAddress getLocalAddress() {
        NetworkInterface result_intf = null, intf;
        InetAddress result_addr = null, addr;
        Enumeration<InetAddress> eips = null;
        Enumeration<NetworkInterface> eintfs = null;

        try {
            eintfs = NetworkInterface.getNetworkInterfaces();
        } catch (SocketException e1) {
            e1.printStackTrace();
        }
        while ((eintfs != null) && eintfs.hasMoreElements()) {
            intf = eintfs.nextElement();
            eips = intf.getInetAddresses();
            while (eips.hasMoreElements()) {
                addr = eips.nextElement();
                debug("INTERFACE " + intf.getName() + "(" + intf.getDisplayName() + ") -> " + addr + "\n\t"
                        + "(Link Local ? " + addr.isLinkLocalAddress() + ") " + "(Loopback ? "
                        + addr.isLoopbackAddress() + ") " + "(Site Local ? " + addr.isSiteLocalAddress() + ") "
                        + "(IPV4 ? " + (addr instanceof Inet4Address) + ") ");

                if (result_addr == null) {
                    result_addr = addr;
                    result_intf = intf;
                    debug(" CHOSEN: result was null");
                } else {
                    if (!(result_addr instanceof Inet4Address) && (addr instanceof Inet4Address)) {
                        result_addr = addr;
                        result_intf = intf;
                        debug(" CHOSEN: address is IPv4");
                    } else if ((result_addr instanceof Inet4Address) == (addr instanceof Inet4Address)) {
                        if (result_addr.isLinkLocalAddress() && !addr.isLinkLocalAddress()) {
                            result_addr = addr;
                            result_intf = intf;
                            debug(" CHOSEN: address wasn't Link Local");
                        } else if (result_addr.isLinkLocalAddress() == addr.isLinkLocalAddress()) {
                            if (result_addr.isLoopbackAddress() && !addr.isLoopbackAddress()) {
                                result_addr = addr;
                                result_intf = intf;
                                debug(" CHOSEN: address wasn't Loopback");
                            } else if (result_addr.isLoopbackAddress() == addr.isLoopbackAddress())
                                if (result_addr.isSiteLocalAddress() && !addr.isSiteLocalAddress()) {
                                    result_addr = addr;
                                    result_intf = intf;
                                    debug(" CHOSEN: address wasn't Site Local");
                                } else if (result_addr.isSiteLocalAddress() == addr.isSiteLocalAddress()) {
                                    String s = intf.getName();
                                    String rs = result_intf.getName();
                                    int snum, rsnum;
                                    int i;
                                    for (i = 0; (i < s.length()) && !Character.isDigit(s.charAt(i)); i++)
                                        ;
                                    if (i < s.length()) {
                                        int begini = i;
                                        for (; i < s.length() && Character.isDigit(s.charAt(i)); i++)
                                            ;
                                        snum = Integer.parseInt(s.substring(begini, i));
                                    } else {
                                        snum = Integer.MAX_VALUE;
                                    }
                                    for (i = 0; (i < rs.length()) && !Character.isDigit(rs.charAt(i)); i++)
                                        ;
                                    if (i < rs.length()) {
                                        int begini = i;
                                        for (; i < rs.length() && Character.isDigit(rs.charAt(i)); i++)
                                            ;
                                        rsnum = Integer.parseInt(rs.substring(begini, i));
                                    } else {
                                        rsnum = Integer.MAX_VALUE;
                                    }

                                    if (snum < rsnum) {
                                        result_addr = addr;
                                        result_intf = intf;
                                        debug(" CHOSEN: interface number was lower");
                                    } else if ((snum == rsnum)
                                            && ((s.length() < rs.length()) || (s.compareTo(rs) < 0))) {
                                        result_addr = addr;
                                        result_intf = intf;
                                        debug(" CHOSEN: interface name was lower");
                                    }
                                }
                        }
                    }
                }
            }
        }

        if (result_addr == null) {
            try {
                result_addr = InetAddress.getByName(null);
                //        result_addr=InetAddress.getLocalHost();
            } catch (UnknownHostException e) {
                e.printStackTrace();
            }
        }

        debug("LOCAL ADDRESS -> " + result_addr);
        return result_addr;
    }

    private static void debug(String s) {
        if (debug != null) {
            debug.println("[HostUtils.getLocalAddress()] :" + s);
        }
    }
}

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