You need to do a reverse DNS lookup for a specific IP address in java

Question

I need to get a DNS address, for example "http://stackoverflow.com/questions/ask" . I used the following code and was able to get as 192.XXX

Hashtable env = new Hashtable(); env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory"); DirContext ictx = new InitialDirContext(env); String dnsServers = (String) ictx.getEnvironment().get("java.naming.provider.url"); System.out.println("DNS Servers: " + dnsServers ); 

Answer 1

 InetAddress ia = InetAddress.getByAddress(new byte[] {74,125,127,106}); // or ia = InetAddress.getByName("74.125.127.106"); System.out.println(ia.getCanonicalHostName()); 

Answer 2

CodingForums similar question - see message # 5 (DISCLAIMER: Code is not mine, not verified by me)

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Code from linked source:

 /** * 25 Nov 2009 REVERSE DNS LOOKUP USING JNDI * In this example the IP being looked up is 211.21.152.4 * The octets are reversed (4.152.21.211) * and appended to the in-addr.arpa zone: * 4.152.21.211.in-addr.arpa */ import javax.naming.*; import javax.naming.directory.*; import java.util.*; public class dns { public static void main(String[] args) { try { Hashtable env = new Hashtable(); env.put("java.naming.factory.initial","com.sun.jndi.dns.DnsContextFactory"); DirContext ctx = new InitialDirContext(env); Attributes attrs = ctx.getAttributes("4.152.21.211.in-addr.arpa",new String[] {"PTR"}); for (NamingEnumeration ae = attrs.getAll();ae.hasMoreElements();) { Attribute attr = (Attribute)ae.next(); String attrId = attr.getID(); for (Enumeration vals = attr.getAll();vals.hasMoreElements(); System.out.println(attrId + ": " + vals.nextElement())); } ctx.close(); } catch(Exception e) { System.out.println("NO REVERSE DNS"); } } } 

Answer 3

I took the code related to @Sam DeHaan, cleaned it up a bit and tested it.

 /** * Do a reverse DNS lookup to find the host name associated with an IP address. Gets results more often than * {@link java.net.InetAddress#getCanonicalHostName()}, but also tries the Inet implementation if reverse DNS does * not work. * * Based on code found at http://www.codingforums.com/showpost.php?p=892349&postcount=5 * * @param ip The IP address to look up * @return The host name, if one could be found, or the IP address */ private static String getHostName(final String ip) { String retVal = null; final String[] bytes = ip.split("\\."); if (bytes.length == 4) { try { final java.util.Hashtable<String, String> env = new java.util.Hashtable<String, String>(); env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory"); final javax.naming.directory.DirContext ctx = new javax.naming.directory.InitialDirContext(env); final String reverseDnsDomain = bytes[3] + "." + bytes[2] + "." + bytes[1] + "." + bytes[0] + ".in-addr.arpa"; final javax.naming.directory.Attributes attrs = ctx.getAttributes(reverseDnsDomain, new String[] { "PTR", }); for (final javax.naming.NamingEnumeration<? extends javax.naming.directory.Attribute> ae = attrs.getAll(); ae.hasMoreElements();) { final javax.naming.directory.Attribute attr = ae.next(); final String attrId = attr.getID(); for (final java.util.Enumeration<?> vals = attr.getAll(); vals.hasMoreElements();) { String value = vals.nextElement().toString(); // System.out.println(attrId + ": " + value); if ("PTR".equals(attrId)) { final int len = value.length(); if (value.charAt(len - 1) == '.') { // Strip out trailing period value = value.substring(0, len - 1); } retVal = value; } } } ctx.close(); } catch (final javax.naming.NamingException e) { // No reverse DNS that we could find, try with InetAddress System.out.print(""); // NO-OP } } if (null == retVal) { try { retVal = java.net.InetAddress.getByName(ip).getCanonicalHostName(); } catch (final java.net.UnknownHostException e1) { retVal = ip; } } return retVal; }