網上一個比較普遍的說法是InetAddress.getLocalHost().getHostAddress()
似乎很簡單，但忽略了一個問題，即IP地址在現在的網路環境更加複雜了，比如有Lan，WIFI，藍芽熱點，虛擬機器網絡卡…
即存在很多的網路介面（network interfaces），每個網路介面就包含一個IP地址，並不是所有的IP地址能被外部或區域網訪問，比如說虛擬機器網絡卡地址等等。
也就是說InetAddress.getLocalHost().getHostAddress()的IP不一定是正確的IP。

寫程式碼前，先明確一些規則：

127.xxx.xxx.xxx 屬於”loopback” 地址，即只能你自己的本機可見，就是本機地址，比較常見的有127.0.0.1；
192.168.xxx.xxx 屬於private 私有地址(site local address)，屬於本地組織內部訪問，只能在本地區域網可見。同樣10.xxx.xxx.xxx、從172.16.xxx.xxx 到 172.31.xxx.xxx都是私有地址，也是屬於組織內部訪問；
169.254.xxx.xxx 屬於連線本地地址（link local IP），在單獨網段可用
從224.xxx.xxx.xxx 到 239.xxx.xxx.xxx 屬於組播地址
比較特殊的255.255.255.255 屬於廣播地址
除此之外的地址就是點對點的可用的公開IPv4地址

獲取本機IP地址的正確姿勢：

複製程式碼
package ipTest;

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 Test {

public Test() {
    // TODO Auto-generated constructor stub
}

public static void main(String[] args) {
    // TODO Auto-generated method stub
    InetAddress ip;
    try {
        // 這種IP容易拿錯
        // System.out.println("Current IP address : " +
        // InetAddress.getLocalHost().getHostAddress());
        // 不一定準確的IP拿法
        // 出自比如這篇：http://www.cnblogs.com/zrui-xyu/p/5039551.html
        System.out.println("get LocalHost Address : " + getLocalHostAddress().getHostAddress());

        // 正確的IP拿法
        System.out.println("get LocalHost LAN Address : " + getLocalHostLANAddress().getHostAddress());


    } catch (UnknownHostException e) {

        e.printStackTrace();

    }
}

// 正確的IP拿法，即優先拿site-local地址
private static InetAddress getLocalHostLANAddress() throws UnknownHostException {
    try {
        InetAddress candidateAddress = null;
        // 遍歷所有的網路介面
        for (Enumeration ifaces = NetworkInterface.getNetworkInterfaces(); ifaces.hasMoreElements();) {
            NetworkInterface iface = (NetworkInterface) ifaces.nextElement();
            // 在所有的介面下再遍歷IP
            for (Enumeration inetAddrs = iface.getInetAddresses(); inetAddrs.hasMoreElements();) {
                InetAddress inetAddr = (InetAddress) inetAddrs.nextElement();
                if (!inetAddr.isLoopbackAddress()) {// 排除loopback型別地址
                    if (inetAddr.isSiteLocalAddress()) {
                        // 如果是site-local地址，就是它了
                        return inetAddr;
                    } else if (candidateAddress == null) {
                        // site-local型別的地址未被發現，先記錄候選地址
                        candidateAddress = inetAddr;
                    }
                }
            }
        }
        if (candidateAddress != null) {
            return candidateAddress;
        }
        // 如果沒有發現 non-loopback地址.只能用最次選的方案
        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;
    }
}

//出自這篇：http://www.cnblogs.com/zrui-xyu/p/5039551.html
//實際上的程式碼是不準的
private static InetAddress getLocalHostAddress() throws UnknownHostException {
    Enumeration allNetInterfaces;
    try {
        allNetInterfaces = NetworkInterface.getNetworkInterfaces();
        InetAddress ip = null;
        while (allNetInterfaces.hasMoreElements()) {
            NetworkInterface netInterface = (NetworkInterface) allNetInterfaces.nextElement();

            Enumeration addresses = netInterface.getInetAddresses();
            while (addresses.hasMoreElements()) {
                ip = (InetAddress) addresses.nextElement();
                if (!ip.isSiteLocalAddress() && !ip.isLoopbackAddress() && ip.getHostAddress().indexOf(":") == -1) {
                    if (ip != null && ip instanceof Inet4Address) {
                        return ip;
                    }
                }
            }
        }
    } catch (SocketException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    InetAddress jdkSuppliedAddress = InetAddress.getLocalHost();
    if (jdkSuppliedAddress == null) {
        throw new UnknownHostException("The JDK InetAddress.getLocalHost() method unexpectedly returned null.");
    }
    return jdkSuppliedAddress;
}
 

}