Modern applications often need the ability to learn information about hosts out on the network. One key class in this process for Java developers is the java.net.InetAddress . This class allows you to figure out various information about hosts, as well as discovering host information by different means.
InetAddress is a deceptively simple class to use, in that it provides a simple API for working with some very complex concepts. For instance, it provides a standard interface for discovering IPv4 IP addresses as well as IPv6 IP addresses. In addition, it distinguishes between multicast and unicast address types transparently. Finally, there are facilities built-in for determining if a host is reachable.
Here are some useful tidbits to understand:
InetAddress will be an Inet6Address object. Likewise, if the address is IPv4, the returned object from the static methods will be an Inet4Address object.byte[] , in which case highest-order byte format is used - so for the ip address 127.0.0.1 , you would have the byte[] {127,0,0,1} .networkaddress.cache.ttl (default: -1)
Indicates the caching policy for successful name lookups from the name service. The value is specified as as integer to indicate the number of seconds to cache the successful lookup.
A value of -1 indicates "cache forever".networkaddress.cache.negative.ttl (default: 10)
Indicates the caching policy for un-successful name lookups from the name service. The value is specified as as integer to indicate the number of seconds to cache the failure for un-successful lookups.
A value of 0 indicates "never cache". A value of -1 indicates "cache forever".
Here is a little example class that shows some of the common techniques for using InetAddress to discover various information:
package org.javalobby.tnt.net; import java.net.InetAddress; public class InetAddressTest { public static void main(String[] args) throws Exception { // Get by host name InetAddress javalobby = InetAddress.getByName("javalobby.org"); // Get by IP as host name InetAddress byIpAsName = InetAddress.getByName("64.69.35.190"); // Get by IP as highest-order byte array InetAddress byIp = InetAddress.getByAddress(new byte[] { 64, 69, 35, (byte)190}); // Get Local address InetAddress local = InetAddress.getLocalHost(); // Get Local Address by Loopback IP InetAddress localByIp = InetAddress.getByName("127.0.0.1"); printAddressInfo("By-Name (Javalobby.org)", javalobby); printAddressInfo("By-Name (Using IP as Host)", byIpAsName); printAddressInfo("By-IP: (64.69.35.190)", byIp); printAddressInfo("Special Local Host", local); printAddressInfo("Local Host By IP", localByIp); } private static void printAddressInfo(String name, InetAddress... hosts) throws Exception { System.out.println("===== Printing Info for: ‘" + name + "‘ ====="); for(InetAddress host : hosts) { System.out.println("Host Name: " + host.getHostName()); System.out.println("Canonical Host Name: " + host.getCanonicalHostName()); System.out.println("Host Address: " + host.getHostAddress()); System.out.println("Calculated Host Address: " + getIpAsString(host)); System.out.print("Is Any Local: " + host.isAnyLocalAddress()); System.out.print(" - Is Link Local: " + host.isLinkLocalAddress()); System.out.print(" - Is Loopback: " + host.isLoopbackAddress()); System.out.print(" - Is Multicast: " + host.isMulticastAddress()); System.out.println(" - Is Site Local: " + host.isSiteLocalAddress()); System.out.println("Is Reachable in 2 seconds: " + host.isReachable(2000)); } } private static String getIpAsString(InetAddress address) { byte[] ipAddress = address.getAddress(); StringBuffer str = new StringBuffer(); for(int i=0; i<ipAddress.length; i++) { if(i > 0) str.append(‘.‘); str.append(ipAddress[i] & 0xFF); } return str.toString(); } }
Here is an example output:
===== Printing Info for: ‘By-Name (Javalobby.org)‘ ===== Host Name: javalobby.org Canonical Host Name: www.javalobby.org Host Address: 64.69.35.190 Calculated Host Address: 64.69.35.190 Is Any Local: false - Is Link Local: false - Is Loopback: false - Is Multicast: false - Is Site Local: false Is Reachable in 2 seconds: true ===== Printing Info for: ‘By-Name (Using IP as Host)‘ ===== Host Name: www.javalobby.org Canonical Host Name: www.javalobby.org Host Address: 64.69.35.190 Calculated Host Address: 64.69.35.190 Is Any Local: false - Is Link Local: false - Is Loopback: false - Is Multicast: false - Is Site Local: false Is Reachable in 2 seconds: true ===== Printing Info for: ‘By-IP: (64.69.35.190)‘ ===== Host Name: www.javalobby.org Canonical Host Name: www.javalobby.org Host Address: 64.69.35.190 Calculated Host Address: 64.69.35.190 Is Any Local: false - Is Link Local: false - Is Loopback: false - Is Multicast: false - Is Site Local: false Is Reachable in 2 seconds: true ===== Printing Info for: ‘Special Local Host‘ ===== Host Name: COFFEE-BYTES-2 Canonical Host Name: 192.168.1.101 Host Address: 192.168.1.101 Calculated Host Address: 192.168.1.101 Is Any Local: false - Is Link Local: false - Is Loopback: false - Is Multicast: false - Is Site Local: true Is Reachable in 2 seconds: true ===== Printing Info for: ‘Local Host By IP‘ ===== Host Name: localhost Canonical Host Name: localhost Host Address: 127.0.0.1 Calculated Host Address: 127.0.0.1 Is Any Local: false - Is Link Local: false - Is Loopback: true - Is Multicast: false - Is Site Local: false Is Reachable in 2 seconds: true Until next time, R.J. Lorimer Contributing Editor - rj -at- javalobby.org Author - http://www.coffee-bytes.com Software Consultant - http://www.crosslogic.com
General: Know How to Use InetAddress
原文：http://www.cnblogs.com/ghgyj/p/4039358.html