Question

import java.net.InetAddress;
import java.net.UnknownHostException;

import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attributes;
import javax.naming.directory.InitialDirContext;

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

            // get the default initial Directory Context
            InitialDirContext iDirC = new InitialDirContext();
            // get the DNS records for inetAddress

            Attributes attributes = iDirC.getAttributes("dns://8.8.8.8/www.google.com", new String[] {"A"});
            // 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();
        }
    }
}

如果我运行此代码，我会收到如下错误...

www.google.com 74.125.128.103
ERROR: No DNS record for 'www.google.com'
javax.naming.CommunicationException: DNS error [Root exception is java.net.SocketTimeoutException: Receive timed out]; remaining name 'www.google.com'
    at com.sun.jndi.dns.DnsClient.query(DnsClient.java:300)
    at com.sun.jndi.dns.Resolver.query(Resolver.java:81)
    at com.sun.jndi.dns.DnsContext.c_getAttributes(DnsContext.java:430)
    at com.sun.jndi.toolkit.ctx.ComponentDirContext.p_getAttributes(ComponentDirContext.java:231)
    at com.sun.jndi.toolkit.ctx.PartialCompositeDirContext.getAttributes(PartialCompositeDirContext.java:139)
    at com.sun.jndi.toolkit.url.GenericURLDirContext.getAttributes(GenericURLDirContext.java:103)
    at javax.naming.directory.InitialDirContext.getAttributes(InitialDirContext.java:142)
    at DNSLookup.main(DNSLookup.java:24)
Caused by: java.net.SocketTimeoutException: Receive timed out
    at java.net.DualStackPlainDatagramSocketImpl.socketReceiveOrPeekData(Native Method)
    at java.net.DualStackPlainDatagramSocketImpl.receive0(DualStackPlainDatagramSocketImpl.java:121)
    at java.net.AbstractPlainDatagramSocketImpl.receive(AbstractPlainDatagramSocketImpl.java:145)
    at java.net.DatagramSocket.receive(DatagramSocket.java:786)
    at com.sun.jndi.dns.DnsClient.doUdpQuery(DnsClient.java:411)
    at com.sun.jndi.dns.DnsClient.query(DnsClient.java:203)
    ... 7 more

但是，如果我使用“dns：/www.google.com”作为查询，而不是“dns：//8.8.8.8/www.google.com”，则它可以正常运行而不会出现任何错误。只有在我尝试指定要使用的DNS服务器时才会出现错误。

“dns：//8.8.8.8/www.google.com” - ＆gt; ERROR

“dns：/www.google.com” - ＆gt;工作！

http://docs.oracle.com/javase/7/docs/technotes/guides/jndi/jndi-dns.html

在本文档中，我想要使用的完全相同。我不明白为什么会出问题。

DirContext ictx = new InitialDirContext();
Attributes attrs3 = ictx.getAttributes("dns://server1.example.com/host3.example.com",
                                   new String[] {"MX"});

Answer 1

您的代码没有任何问题，但我怀疑您是在阻止传出DNS的代理或防火墙后面运行它。

当您要求dns:/www.google.com时，您实际上是在向本地DHCP提供的解析程序询问www.google.com的IP - 就像在浏览器地址行中键入地址一样。

但是，在使用dns://8.8.8.8/www.google.com时，您要求使用Google DNS解析google.com，这要求您的代理/防火墙允许传出TCP / UDP端口53流量，这通常不是企业环境......

干杯，

Java JNDI DNS错误：“接收超时”

1 个答案: