Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE * file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file * to you 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 * <p> * http://www.apache.org/licenses/LICENSE-2.0 * <p> * 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. */ package com.buaa.cfs.net; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import javax.naming.NamingException; import javax.naming.directory.Attributes; import javax.naming.directory.DirContext; import javax.naming.directory.InitialDirContext; import java.net.InetAddress; import java.net.NetworkInterface; import java.net.SocketException; import java.net.UnknownHostException; import java.util.Collections; import java.util.Enumeration; import java.util.LinkedHashSet; import java.util.Vector; /** * A class that provides direct and reverse lookup functionalities, allowing the querying of specific network interfaces * or nameservers. */ public class DNS { private static final Log LOG = LogFactory.getLog(DNS.class); /** * The cached hostname -initially null. */ private static final String cachedHostname = resolveLocalHostname(); private static final String cachedHostAddress = resolveLocalHostIPAddress(); private static final String LOCALHOST = "localhost"; /** * Returns the hostname associated with the specified IP address by the provided nameserver. * <p> * Loopback addresses * * @param hostIp The address to reverse lookup * @param ns The host name of a reachable DNS server * * @return The host name associated with the provided IP * * @throws NamingException If a NamingException is encountered */ public static String reverseDns(InetAddress hostIp, String ns) throws NamingException { // // Builds the reverse IP lookup form // This is formed by reversing the IP numbers and appending in-addr.arpa // String[] parts = hostIp.getHostAddress().split("\\."); String reverseIP = parts[3] + "." + parts[2] + "." + parts[1] + "." + parts[0] + ".in-addr.arpa"; DirContext ictx = new InitialDirContext(); Attributes attribute; try { attribute = ictx.getAttributes("dns://" // Use "dns:///" if the default + ((ns == null) ? "" : ns) + // nameserver is to be used "/" + reverseIP, new String[] { "PTR" }); } finally { ictx.close(); } String hostname = attribute.get("PTR").get().toString(); int hostnameLength = hostname.length(); if (hostname.charAt(hostnameLength - 1) == '.') { hostname = hostname.substring(0, hostnameLength - 1); } return hostname; } /** * @return NetworkInterface for the given subinterface name (eg eth0:0) or null if no interface with the given name * can be found */ private static NetworkInterface getSubinterface(String strInterface) throws SocketException { Enumeration<NetworkInterface> nifs = NetworkInterface.getNetworkInterfaces(); while (nifs.hasMoreElements()) { Enumeration<NetworkInterface> subNifs = nifs.nextElement().getSubInterfaces(); while (subNifs.hasMoreElements()) { NetworkInterface nif = subNifs.nextElement(); if (nif.getName().equals(strInterface)) { return nif; } } } return null; } /** * @param nif network interface to get addresses for * * @return set containing addresses for each subinterface of nif, see below for the rationale for using an ordered * set */ private static LinkedHashSet<InetAddress> getSubinterfaceInetAddrs(NetworkInterface nif) { LinkedHashSet<InetAddress> addrs = new LinkedHashSet<InetAddress>(); Enumeration<NetworkInterface> subNifs = nif.getSubInterfaces(); while (subNifs.hasMoreElements()) { NetworkInterface subNif = subNifs.nextElement(); addrs.addAll(Collections.list(subNif.getInetAddresses())); } return addrs; } /** * Like {@link DNS#getIPs(String, boolean), but returns all IPs associated with the given interface and its * subinterfaces. */ public static String[] getIPs(String strInterface) throws UnknownHostException { return getIPs(strInterface, true); } /** * Returns all the IPs associated with the provided interface, if any, in textual form. * * @param strInterface The name of the network interface or sub-interface to query (eg eth0 or eth0:0) or the * string "default" * @param returnSubinterfaces Whether to return IPs associated with subinterfaces of the given interface * * @return A string vector of all the IPs associated with the provided interface. The local host IP is returned if * the interface name "default" is specified or there is an I/O error looking for the given interface. * * @throws UnknownHostException If the given interface is invalid */ public static String[] getIPs(String strInterface, boolean returnSubinterfaces) throws UnknownHostException { if ("default".equals(strInterface)) { return new String[] { cachedHostAddress }; } NetworkInterface netIf; try { netIf = NetworkInterface.getByName(strInterface); if (netIf == null) { netIf = getSubinterface(strInterface); } } catch (SocketException e) { LOG.warn("I/O error finding interface " + strInterface + ": " + e.getMessage()); return new String[] { cachedHostAddress }; } if (netIf == null) { throw new UnknownHostException("No such interface " + strInterface); } // NB: Using a LinkedHashSet to preserve the order for callers // that depend on a particular element being 1st in the array. // For example, getDefaultIP always returns the first element. LinkedHashSet<InetAddress> allAddrs = new LinkedHashSet<InetAddress>(); allAddrs.addAll(Collections.list(netIf.getInetAddresses())); if (!returnSubinterfaces) { allAddrs.removeAll(getSubinterfaceInetAddrs(netIf)); } String ips[] = new String[allAddrs.size()]; int i = 0; for (InetAddress addr : allAddrs) { ips[i++] = addr.getHostAddress(); } return ips; } /** * Returns the first available IP address associated with the provided network interface or the local host IP if * "default" is given. * * @param strInterface The name of the network interface or subinterface to query (e.g. eth0 or eth0:0) or the * string "default" * * @return The IP address in text form, the local host IP is returned if the interface name "default" is specified * * @throws UnknownHostException If the given interface is invalid */ public static String getDefaultIP(String strInterface) throws UnknownHostException { String[] ips = getIPs(strInterface); return ips[0]; } /** * Returns all the host names associated by the provided nameserver with the address bound to the specified network * interface * * @param strInterface The name of the network interface or subinterface to query (e.g. eth0 or eth0:0) * @param nameserver The DNS host name * * @return A string vector of all host names associated with the IPs tied to the specified interface * * @throws UnknownHostException if the given interface is invalid */ public static String[] getHosts(String strInterface, String nameserver) throws UnknownHostException { String[] ips = getIPs(strInterface); Vector<String> hosts = new Vector<String>(); for (int ctr = 0; ctr < ips.length; ctr++) { try { hosts.add(reverseDns(InetAddress.getByName(ips[ctr]), nameserver)); } catch (UnknownHostException ignored) { } catch (NamingException ignored) { } } if (hosts.isEmpty()) { LOG.warn("Unable to determine hostname for interface " + strInterface); return new String[] { cachedHostname }; } else { return hosts.toArray(new String[hosts.size()]); } } /** * Determine the local hostname; retrieving it from cache if it is known If we cannot determine our host name, * return "localhost" * * @return the local hostname or "localhost" */ private static String resolveLocalHostname() { String localhost; try { localhost = InetAddress.getLocalHost().getCanonicalHostName(); } catch (UnknownHostException e) { LOG.warn("Unable to determine local hostname " + "-falling back to \"" + LOCALHOST + "\"", e); localhost = LOCALHOST; } return localhost; } /** * Get the IPAddress of the local host as a string. This will be a loop back value if the local host address cannot * be determined. If the loopback address of "localhost" does not resolve, then the system's network is in such a * state that nothing is going to work. A message is logged at the error level and a null pointer returned, a * pointer which will trigger failures later on the application * * @return the IPAddress of the local host or null for a serious problem. */ private static String resolveLocalHostIPAddress() { String address; try { address = InetAddress.getLocalHost().getHostAddress(); } catch (UnknownHostException e) { LOG.warn("Unable to determine address of the host" + "-falling back to \"" + LOCALHOST + "\" address", e); try { address = InetAddress.getByName(LOCALHOST).getHostAddress(); } catch (UnknownHostException noLocalHostAddressException) { //at this point, deep trouble LOG.error("Unable to determine local loopback address " + "of \"" + LOCALHOST + "\" " + "-this system's network configuration is unsupported", e); address = null; } } return address; } /** * Returns all the host names associated by the default nameserver with the address bound to the specified network * interface * * @param strInterface The name of the network interface to query (e.g. eth0) * * @return The list of host names associated with IPs bound to the network interface * * @throws UnknownHostException If one is encountered while querying the default interface */ public static String[] getHosts(String strInterface) throws UnknownHostException { return getHosts(strInterface, null); } /** * Returns the default (first) host name associated by the provided nameserver with the address bound to the * specified network interface * * @param strInterface The name of the network interface to query (e.g. eth0) * @param nameserver The DNS host name * * @return The default host names associated with IPs bound to the network interface * * @throws UnknownHostException If one is encountered while querying the default interface */ public static String getDefaultHost(String strInterface, String nameserver) throws UnknownHostException { if ("default".equals(strInterface)) { return cachedHostname; } if ("default".equals(nameserver)) { return getDefaultHost(strInterface); } String[] hosts = getHosts(strInterface, nameserver); return hosts[0]; } /** * Returns the default (first) host name associated by the default nameserver with the address bound to the * specified network interface * * @param strInterface The name of the network interface to query (e.g. eth0). Must not be null. * * @return The default host name associated with IPs bound to the network interface * * @throws UnknownHostException If one is encountered while querying the default interface */ public static String getDefaultHost(String strInterface) throws UnknownHostException { return getDefaultHost(strInterface, null); } }