Java DNSLookup get DNS attributes

问题

I'm quite new to the network DNS records and need a program that can run lookup to get 3 main DNS records of a domain (A,MX,NS).

I have been looking for a java solution here an there and my final class is as below: However, I will always get a NameException and can't find the reason for it.

[EDIT]: The problem seem to be with our internet, because using other wifi, the program run just fine.

Many thanks,

import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
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
{
    public static void main(String args[])
    {
        String host = "google.com";
        try
        {
            InetAddress inetAddress = InetAddress.getByName(host);
            // show the Internet Address as name/address
            System.out.println(inetAddress.getHostName() + " " + inetAddress.getHostAddress());

            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
            InitialDirContext iDirC = new InitialDirContext(env);
            // 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();
            System.out.println("");
            while (attributeEnumeration.hasMore())
            {
                System.out.println("" + attributeEnumeration.next());
            }
            attributeEnumeration.close();
        }
        catch (UnknownHostException exception)
        {
            System.err.println("ERROR: Cannot access '" + host + "'");
        }
        catch (NamingException exception)
        {
            System.err.println("ERROR: No DNS record for '" + host + "'");
            exception.printStackTrace();
        }
    }
}

Output:

google.com 74.125.128.113
ERROR: No DNS record for 'google.com'
javax.naming.CommunicationException: DNS error [Root exception is java.net.SocketTimeoutException: Receive timed out]; remaining name 'google.com'
    at com.sun.jndi.dns.DnsClient.query(Unknown Source)
    at com.sun.jndi.dns.Resolver.query(Unknown Source)
    at com.sun.jndi.dns.DnsContext.c_getAttributes(Unknown Source)
    at com.sun.jndi.toolkit.ctx.ComponentDirContext.p_getAttributes(Unknown Source)
    at com.sun.jndi.toolkit.ctx.PartialCompositeDirContext.getAttributes(Unknown Source)
    at com.sun.jndi.toolkit.url.GenericURLDirContext.getAttributes(Unknown Source)
    at javax.naming.directory.InitialDirContext.getAttributes(Unknown Source)
    at javax.naming.directory.InitialDirContext.getAttributes(Unknown Source)
    at gimasys.dnsCrawler.DNSLookup.main(DNSLookup.java:35)
Caused by: java.net.SocketTimeoutException: Receive timed out
    at java.net.DualStackPlainDatagramSocketImpl.socketReceiveOrPeekData(Native Method)
    at java.net.DualStackPlainDatagramSocketImpl.receive0(Unknown Source)
    at java.net.AbstractPlainDatagramSocketImpl.receive(Unknown Source)
    at java.net.DatagramSocket.receive(Unknown Source)
    at com.sun.jndi.dns.DnsClient.doUdpQuery(Unknown Source)
    ... 9 more

回答1:

I have tried with provided class (DNSLookup.java), it's working for me.

My underestanding is it's giving timeOut exception, means its not able to connect to server.

Check your internet connection ?

来源：https://stackoverflow.com/questions/15239220/java-dnslookup-get-dns-attributes