source: branches/OKBJavaConnector/ECJClient/src/ec/util/LocalHost.java @ 6152

package ec.util;

import java.net.*;
import java.util.*;

/**
 * Modified from <a href="http://mail-archives.apache.org/mod_mbox/jakarta-jcs-dev/200803.mbox/%3C1066089445.1204637680849.JavaMail.jira@brutus%3E">
 * apache mail-archives</a>. 
 *
 * This code was published in the public domain, but I believe it was probably intended to be
 * distributed under the Apache license, like the rest of the Jakarta code.  That license is
 * listed at the end of this file.
 *
 */
 
public class LocalHost 
    {
    /**
     * Returns an <code>InetAddress</code> object encapsulating what is most
     * likely the machine's LAN IP address. <p/> This method is intended for use
     * as a replacement of JDK method <code>InetAddress.getLocalHost</code>,
     * because that method is ambiguous on Linux systems. Linux systems
     * enumerate the loopback network interface the same way as regular LAN
     * network interfaces, but the JDK <code>InetAddress.getLocalHost</code>
     * method does not specify the algorithm used to select the address returned
     * under such circumstances, and will often return the loopback address,
     * which is not valid for network communication. Details <a
     * href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4665037"
     * >here</a>. <p/> This method will scan all IP addresses on all network
     * interfaces on the host machine to determine the IP address most likely to
     * be the machine's LAN address. If the machine has multiple IP addresses,
     * this method will prefer a site-local IP address (e.g. 192.168.x.x or
     * 10.10.x.x, usually IPv4) if the machine has one (and will return the
     * first site-local address if the machine has more than one), but if the
     * machine does not hold a site-local address, this method will return
     * simply the first non-loopback address found (IPv4 or IPv6). <p/> If this
     * method cannot find a non-loopback address using this selection algorithm,
     * it will fall back to calling and returning the result of JDK method
     * <code>InetAddress.getLocalHost</code>. <p/>
     * 
     * @throws UnknownHostException
     *             If the LAN address of the machine cannot be found.
     */
    public static InetAddress getLocalHost() throws UnknownHostException 
        {
        try 
            {
            InetAddress candidateAddress = null;
            // Iterate all NICs (network interface cards)...
            for (Enumeration ifaces = NetworkInterface.getNetworkInterfaces(); ifaces.hasMoreElements();)
                {
                NetworkInterface iface = (NetworkInterface) ifaces.nextElement();
                // Iterate all IP addresses assigned to each card...
                for (Enumeration inetAddrs = iface.getInetAddresses(); inetAddrs.hasMoreElements();)
                    {
                    InetAddress inetAddr = (InetAddress) inetAddrs.nextElement();
                    if (!inetAddr.isLoopbackAddress()) 
                        {
                        if (inetAddr.isSiteLocalAddress()) return inetAddr;  // Found non-loopback site-local address.

                        // Found non-loopback address, but not necessarily site-local.
                        // Store it as a candidate to be returned if site-local address is not subsequently found...
                        // Note that we don't repeatedly assign non-loopback non-site-local addresses as candidates,
                        // only the first. For subsequent iterations, candidate will be non-null.
                        else if (candidateAddress == null) candidateAddress = inetAddr;
                        }
                    }
                }
            // We did not find a site-local address, but we found some other non-loopback address.
            // Server might have a non-site-local address assigned to its NIC (or it might be running
            // IPv6 which deprecates the "site-local" concept).
            // Return this non-loopback candidate address...
            if (candidateAddress != null) return candidateAddress;

            // At this point, we did not find a non-loopback address.
            // Fall back to returning whatever InetAddress.getLocalHost() returns...
            InetAddress jdkSuppliedAddress = InetAddress.getLocalHost();
            if (jdkSuppliedAddress == null)
                throw new UnknownHostException("The JDK InetAddress.getLocalHost() method unexpectedly returned null.");
            return jdkSuppliedAddress;
            }
        catch (Exception e) 
            {
            UnknownHostException unknownHostException = new UnknownHostException("Failed to determine LAN address: " + e);
            unknownHostException.initCause(e);
            throw unknownHostException;
            }
        }
    }



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