Java DNSLookup MX record list. Like MXToolBox

Question

I'm building a program to list all MX record of a domain. It seemed to work fine at first, but after comparing to a online tool http://mxtoolbox.com/. There are domain that the program can not get MX record while MXToolbox can.

I'm not sure what the reason is or any configuration that required.

Many thanks;

Here is my code.

import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.InitialDirContext;
import javax.naming.Context;
import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Hashtable;

public class DNSLookup
{
    private InitialDirContext iDirC;

    public DNSLookup ()
    {
         Hashtable<String, String> env = new Hashtable<String, String>();
         //env.put(Context.INITIAL_CONTEXT_FACTORY,"com.sun.jndi.ldap.LdapCtxFactory");
         //env.put(Context.PROVIDER_URL, "ldap://localhost:389/o=JNDITutorial");
         env.put(Context.INITIAL_CONTEXT_FACTORY,"com.sun.jndi.dns.DnsContextFactory");
         //env.put(Context.PROVIDER_URL, "dns://google.com");
         // get the default initial Directory Context
         try {
            iDirC = new InitialDirContext(env);
        } catch (NamingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    private void lookup (String host, String record)
    {
        InetAddress inetAddress;
        try {
            inetAddress = InetAddress.getByName(host);
            // show the Internet Address as name/address
            System.out.println(inetAddress.getHostName() + " " + inetAddress.getHostAddress());

            // get the DNS records for inetAddress
            Attributes attributes = iDirC.getAttributes("dns:\\"+inetAddress.getHostName());
            // get an enumeration of the attributes and print them out
            //NamingEnumeration<?> attributeEnumeration = attributes.getAll();
/*          while (attributeEnumeration.hasMore())
            {
                System.out.println("" + attributeEnumeration.next());
            }
            attributeEnumeration.close();*/
            Attribute mxRecord = attributes.get(record);
            for (int i=0; i<mxRecord.size();i++)
                System.out.println(mxRecord.get(i));

        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (NamingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public static void main(String[] args){
        DNSLookup looker = new DNSLookup();
        looker.lookup("truetech.com", "MX");
    }
}

The above domain will output NullPointer mean no MX record found. While the MXToolBox will output one.

Answer 1

I know this is a late answer (but I hope this helps you or someone else).

Here's a working solution on how you can find MX Records. The solution hinges off IntialDirContext and goes on to use Attributes to define what type of attribute is required.

// Print out a sorted list of mail exchange servers for a network domain name
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.InitialDirContext;
import javax.naming.NamingException;
import java.util.Arrays;
import java.util.Comparator;

public class MailHostsLookup 
{
    public static void main(String args[]) 
    {
        // explain what program does and how to use it 
        if (args.length != 1)
        {
            System.err.println("Print out a sorted list of mail exchange servers ");
            System.err.println("    for a network domain name");
            System.err.println("USAGE: java MailHostsLookup domainName");
            System.exit(-1);
        } 
        try
        {   // print the sorted mail exhchange servers
            for (String mailHost: lookupMailHosts(args[0]))
            {
                System.out.println(mailHost);            
            }
        }
        catch (NamingException e)
        {
            System.err.println("ERROR: No DNS record for '" + args[0] + "'");
            System.exit(-2);
        }
     }

    // returns a String array of mail exchange servers (mail hosts) 
    //     sorted from most preferred to least preferred
    static String[] lookupMailHosts(String domainName) throws NamingException
    {
        // see: RFC 974 - Mail routing and the domain system
        // see: RFC 1034 - Domain names - concepts and facilities
        // see: http://java.sun.com/j2se/1.5.0/docs/guide/jndi/jndi-dns.html
        //    - DNS Service Provider for the Java Naming Directory Interface (JNDI)

        // get the default initial Directory Context
        InitialDirContext iDirC = new InitialDirContext();
        // get the MX records from the default DNS directory service provider
        //    NamingException thrown if no DNS record found for domainName
        Attributes attributes = iDirC.getAttributes("dns:/" + domainName, new String[] {"MX"});
        // attributeMX is an attribute ('list') of the Mail Exchange(MX) Resource Records(RR)
        Attribute attributeMX = attributes.get("MX");

        // if there are no MX RRs then default to domainName (see: RFC 974)
        if (attributeMX == null)
        {
            return (new String[] {domainName});
        }

        // split MX RRs into Preference Values(pvhn[0]) and Host Names(pvhn[1])
        String[][] pvhn = new String[attributeMX.size()][2];
        for (int i = 0; i < attributeMX.size(); i++)
        {
            pvhn[i] = ("" + attributeMX.get(i)).split("\\s+");
        }

        // sort the MX RRs by RR value (lower is preferred)
        Arrays.sort(pvhn, new Comparator<String[]>()
            {
                public int compare(String[] o1, String[] o2)
                {
                    return (Integer.parseInt(o1[0]) - Integer.parseInt(o2[0]));
                }
            });

        // put sorted host names in an array, get rid of any trailing '.' 
        String[] sortedHostNames = new String[pvhn.length];
        for (int i = 0; i < pvhn.length; i++)
        {
            sortedHostNames[i] = pvhn[i][1].endsWith(".") ? 
                pvhn[i][1].substring(0, pvhn[i][1].length() - 1) : pvhn[i][1];
        }
        return sortedHostNames;
    }
}