Java DNSLookup MX记录列表.像MXToolBox [英] Java DNSLookup MX record list. Like MXToolBox

问题描述

我正在构建一个程序来列出域的所有MX记录.起初它似乎工作正常，但与在线工具 http://mxtoolbox.com/进行比较之后.在某些域中，程序无法获得MX记录，而MXToolbox可以.

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.

我不确定是什么原因或所需的任何配置.

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

非常感谢；

这是我的代码.

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");
    }
}

以上域将输出NullPointer，表示未找到MX记录.而MXToolBox将输出一个.

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

推荐答案

我知道这是一个较晚的答案(但希望对您或其他人有帮助).

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

这是有关如何找到MX记录的有效解决方案.该解决方案取决于IntialDirContext并继续使用Attributes定义所需的属性类型.

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;
    }
}

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