获得ip地址[转载]

首先，你如果搜索“JAVA获取本机IP地址”，基本上搜到的资料全是无用的。 
比如这篇：http://www.cnblogs.com/zrui-xyu/p/5039551.html 
实际上的代码在复杂环境下是不准的

网上一个比较普遍的说法是InetAddress.getLocalHost().getHostAddress() 
似乎很简单，但忽略了一个问题，即IP地址在现在的网络环境更加复杂了，比如有Lan，WIFI，蓝牙热点，虚拟机网卡… 
即存在很多的网络接口（network interfaces），每个网络接口就包含一个IP地址，并不是所有的IP地址能被外部或局域网访问，比如说虚拟机网卡地址等等。 
也就是说InetAddress.getLocalHost().getHostAddress()的IP不一定是正确的IP。

写代码前，先明确一些规则：

127.xxx.xxx.xxx 属于”loopback” 地址，即只能你自己的本机可见，就是本机地址，比较常见的有127.0.0.1； 
192.168.xxx.xxx 属于private 私有地址(site local address)，属于本地组织内部访问，只能在本地局域网可见。同样10.xxx.xxx.xxx、从172.16.xxx.xxx 到 172.31.xxx.xxx都是私有地址，也是属于组织内部访问； 
169.254.xxx.xxx 属于连接本地地址（link local IP），在单独网段可用 
从224.xxx.xxx.xxx 到 239.xxx.xxx.xxx 属于组播地址 
比较特殊的255.255.255.255 属于广播地址 
除此之外的地址就是点对点的可用的公开IPv4地址

获取本机IP地址的正确姿势：

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

public static void main(String[] args) {
    // TODO Auto-generated method stub
    InetAddress ip;
    try {
        // 这种IP容易拿错
        // System.out.println("Current IP address : " +
        // InetAddress.getLocalHost().getHostAddress());
        // 不一定准确的IP拿法
        // 出自比如这篇：http://www.cnblogs.com/zrui-xyu/p/5039551.html
        System.out.println("get LocalHost Address : " + getLocalHostAddress().getHostAddress());

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


    } catch (UnknownHostException e) {

        e.printStackTrace();

    }
}

// 正确的IP拿法，即优先拿site-local地址
private static InetAddress getLocalHostLANAddress() throws UnknownHostException {
    try {
        InetAddress candidateAddress = null;
        // 遍历所有的网络接口
        for (Enumeration ifaces = NetworkInterface.getNetworkInterfaces(); ifaces.hasMoreElements();) {
            NetworkInterface iface = (NetworkInterface) ifaces.nextElement();
            // 在所有的接口下再遍历IP
            for (Enumeration inetAddrs = iface.getInetAddresses(); inetAddrs.hasMoreElements();) {
                InetAddress inetAddr = (InetAddress) inetAddrs.nextElement();
                if (!inetAddr.isLoopbackAddress()) {// 排除loopback类型地址
                    if (inetAddr.isSiteLocalAddress()) {
                        // 如果是site-local地址，就是它了
                        return inetAddr;
                    } else if (candidateAddress == null) {
                        // site-local类型的地址未被发现，先记录候选地址
                        candidateAddress = inetAddr;
                    }
                }
            }
        }
        if (candidateAddress != null) {
            return candidateAddress;
        }
        // 如果没有发现 non-loopback地址.只能用最次选的方案
        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;
    }
}

//出自这篇：http://www.cnblogs.com/zrui-xyu/p/5039551.html
//实际上的代码是不准的
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;