Java：JAVA API域名解析说明

我不是女神ヾ 2024-03-22 21:40 17阅读 0赞

java常用的域名解析的方式是使用InetAddress中的如下2个方法：

> InetAddress.getByName(String host);  
> InetAddress.getAllByName(String host);

以上方法的最大问题是不知道有几个域名服务器，以及IP是从哪个域名服务器解析出来的。

可以通过下面的代码先获取域名服务器的地址，然后从这些域名服务器分别获取解析出来的IP：

import java.util.ArrayList;
    import java.util.Hashtable;
    import java.util.LinkedHashMap;
    import java.util.List;
    import java.util.Map;
    
    import javax.naming.Context;
    import javax.naming.NamingEnumeration;
    import javax.naming.NamingException;
    import javax.naming.directory.Attribute;
    import javax.naming.directory.Attributes;
    import javax.naming.directory.DirContext;
    import javax.naming.directory.InitialDirContext;
    
    public class DnsTester {
    
     // 获取默认的DNS服务器
     public static String[] getDnsNameServerUrlArray() {
    
      Hashtable<String, String> env = new Hashtable<String, String>();
      env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
      env.put(Context.PROVIDER_URL, "dns://");
    
      try {
       DirContext ctx = new InitialDirContext(env);
       String dndUrls = (String) ctx.getEnvironment().get(Context.PROVIDER_URL);
    
       System.out.println(dndUrls);
    
       return dndUrls.split(" ");
      } catch (NamingException e) {
       e.printStackTrace();
      }
    
      return new String[0];
     }
    
     // 使用DNS服务器解析域名
     public static Map<String, List<String>> getIpList(String domainName) {
      Map<String, List<String>> resultMap = new LinkedHashMap<>();
    
      for (String dnsUrl : getDnsNameServerUrlArray()) {
       List<String> results = new ArrayList<>();
       try {
        Hashtable<String, String> env = new Hashtable<String, String>();
        env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
        env.put(Context.PROVIDER_URL, dnsUrl);
    
        DirContext ctx = new InitialDirContext(env);
    
        Attributes attrs = ctx.getAttributes(domainName, new String[] { "A" });
    
        for (NamingEnumeration<? extends Attribute> e = attrs.getAll(); e.hasMoreElements();) {
         Attribute a = e.nextElement();
         int size = a.size();
         for (int i = 0; i < size; i++) {
          results.add((String) a.get(i));
         }
        }
    
        resultMap.put(dnsUrl, results);
    
        System.out.println(dnsUrl + ": DNS resolve OK");
       } catch (NamingException e) {
        System.out.println(dnsUrl + ": " + e.getMessage());
       }
      }
    
      return resultMap;
     }
    
     public static void main(String[] args) throws NamingException {
      String domainName = "baidu.com";
    
      if (args.length > 0) {
       domainName = args[0];
      }
      Map<String, List<String>> ipList = getIpList(domainName);
    
      System.out.println(domainName + ": " + ipList);
     }
    
    }

执行命令

> java DnsTester 163.com

运行的结果如下：

> dns://25.11.1.3 dns://25.11.1.4 dns://221.179.155.161 dns://221.179.155.177
> 
> dns://25.11.1.3: DNS name not found \[response code 3\]
> 
> dns://25.11.1.4: DNS name not found \[response code 3\]
> 
> dns://221.179.155.161: DNS resolve OK
> 
> dns://221.179.155.177: DNS resolve OK
> 
> 163.com: \{dns://221.179.155.161=\[123.58.180.8, 123.58.180.7\], dns://221.179.155.177=\[123.58.180.7, 123.58.180.8\]\}

参考文档

[DNS Service Provider for the Java Naming Directory Interface (JNDI)][DNS Service Provider for the Java Naming Directory Interface _JNDI]

[DNS Service Provider for the Java Naming Directory Interface _JNDI]: https://docs.oracle.com/javase/8/docs/technotes/guides/jndi/jndi-dns.html