Java Host Address Get getHostAddressFromProperty(final String property)

Description

Return the local host address based on the value of a system property.

License

Apache License

Parameter

Parameter	Description
property	The property name to use

Exception

Parameter	Description
UnknownHostException	if no IP address for the host name could be found.

Return

The local host address

Declaration

public static String getHostAddressFromProperty(final String property) throws UnknownHostException 

Method Source Code

//package com.java2s;
/*/* ww w.  ja v  a  2 s  .  c om*/
 * Copyright to the original author or authors
 *
 * 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.
 */

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

public class Main {
    /**
     * Return the local host address based on the value of a system property.
     * using {@link java.net.InetAddress#getByName(String)}. If the system
     * property is not resolvable, return the first non-loopback address. If there are no non-loopback addresses,
     * return the default host address obtained from {@link java.net.InetAddress#getLocalHost()}.
     *
     * @param property The property name to use
     *
     * @return The local host address
     *
     * @throws UnknownHostException if no IP address for the host name could be found.
     */
    public static String getHostAddressFromProperty(final String property) throws UnknownHostException {
        return getInetAddressFromProperty(property).getHostAddress();
    }

    /**
     * Return the local host address for a passed in host using
     * {@link java.net.InetAddress#getByName(String)}
     *
     * @param name The name of the host to return
     *
     * @return The local host address
     *
     * @throws UnknownHostException if no IP address for the host name
     * could be found.
     */
    public static String getHostAddress(final String name) throws UnknownHostException {
        return InetAddress.getByName(name).getHostAddress();
    }

    /**
     * Return the {@code InetAddress} based on the value of a system property.
     * using {@link java.net.InetAddress#getByName(String)}. If the system
     * property is not resolvable, return the first non-loopback address. If there are no non-loopback addresses,
     * return the default host address obtained from {@link java.net.InetAddress#getLocalHost()}.
     *
     * @param property The property name to use
     *
     * @return The local host address
     *
     * @throws UnknownHostException if no IP address for the host name could be found.
     */
    public static InetAddress getInetAddressFromProperty(final String property) throws UnknownHostException {
        InetAddress inetAddress = getInetAddress();
        String value = System.getProperty(property);
        if (value != null) {
            inetAddress = InetAddress.getByName(value);
        }
        return inetAddress;
    }

    /**
     * Return the local host address
     *
     * @return The first non-loopback address. If there are no non-loopback addresses,
     * return the default host address obtained from {@link java.net.InetAddress#getLocalHost()}.
     *
     * @throws UnknownHostException if no IP address for the local host could be found.
     */
    public static InetAddress getInetAddress() throws UnknownHostException {
        InetAddress address = null;
        try {
            address = getFirstNonLoopbackAddress(false, false);
        } catch (SocketException e) {
            e.printStackTrace();
        }
        if (address == null) {
            address = InetAddress.getLocalHost();
        }
        return address;
    }

    /**
     * Get the first non-loopback address.
     *
     * @param preferIpv4 If you want the Internet Protocol version 4 (IPv4) address, this value must be {@code true}.
     * @param preferIPv6 If you want the  Internet Protocol version 6 (IPv6) address, this value must be {@code true}.
     *                   If the {@code preferIpv4} is set to {@code true}, this value is ignored
     * @return The first non loopback address or {@code null} if there are no non-loopback addresses.
     * @throws SocketException If an I/O error occurs.
     */
    public static InetAddress getFirstNonLoopbackAddress(boolean preferIpv4, boolean preferIPv6)
            throws SocketException {
        Enumeration en = NetworkInterface.getNetworkInterfaces();
        while (en.hasMoreElements()) {
            NetworkInterface i = (NetworkInterface) en.nextElement();
            for (Enumeration en2 = i.getInetAddresses(); en2.hasMoreElements();) {
                InetAddress addr = (InetAddress) en2.nextElement();
                if (!addr.isLoopbackAddress()) {
                    if (addr instanceof Inet4Address) {
                        if (preferIPv6) {
                            continue;
                        }
                        if (preferIpv4)
                            return addr;
                    }
                    if (addr instanceof Inet6Address) {
                        if (preferIpv4) {
                            continue;
                        }
                        if (preferIPv6)
                            return addr;
                    } else
                        return addr;
                }
            }
        }
        return null;
    }
}

Related

1. getHostAddress(String hostname)
2. getHostAddress(String hostPort)
3. getHostAddresses()
4. getHostAddresses()
5. getHostAddresses()
6. getHostExternalAddr()
7. getHostName(String addr)
8. getHostName(String address)
9. getHostName(String address)