アドレスを調べる

GetIPAddress.java

import java.net.*;
public class GetIPAddress {
    public static void main(String[] args) {
        String server_name = "localhost";
        if (args.length > 0) {
            server_name = args[0];
        }
        try {
            InetAddress ia = InetAddress.getByName(server_name);
            System.out.println("host name: " + ia.getHostName());
            System.out.println("IP address: " + ia.getHostAddress());
        } catch (java.io.IOException e) {
            e.printStackTrace();
            return;
        }
    }

// 実行:
// % java GetIPAddress www.yahoo.co.jp
// host name: www.yahoo.co.jp
// IP address: 124.83.171.240

// % java GetIPAddress 124.83.171.240 
// host name: f7.top.vip.ogk.yahoo.co.jp
// IP address: 124.83.171.240

// % java GetIPAddress localhost         
// host name: localhost
// IP address: 127.0.0.1

// % java GetIPAddress www.yaaaahoo.co.jp // 存在しないホスト
// java.net.UnknownHostException: www.yaaaahoo.co.jp
//     at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
//     at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:848)
//     at java.net.InetAddress.getAddressFromNameService(InetAddress.java:1201)
//     at java.net.InetAddress.getAllByName0(InetAddress.java:1152)
//     at java.net.InetAddress.getAllByName(InetAddress.java:1082)
//     at java.net.InetAddress.getAllByName(InetAddress.java:1018)
//     at java.net.InetAddress.getByName(InetAddress.java:968)
//     at GetIPAddress.main(GetIPAddress.java:9)