如何配置主机名解析以在Java中使用自定义DNS服务器？

Question

Java语言网默认情况下，InetAddress使用本地计算机的默认主机名解析程序解析主机名：

主机名到IP地址的解析是通过使用本地机器配置信息和网络命名服务（如域名系统（DNS）和网络信息服务（NIS））的组合来实现的。默认情况下，正在使用的特定命名服务是本地计算机配置的服务。对于任何主机名，都会返回其相应的IP地址^[来源]

我们如何在不修改本地机器的默认主机名解析器的情况下配置此行为？

例如，是否有配置java的方法。网InetAddress，以便通过OpenDNS（208.67.222.222208.67.220.220）或谷歌公共DNS（2001:4860:4860：：8882001:4860:4860：：8844）解析主机名？

或者是显式创建DNS数据包请求、通过java.net.DatagramSocket或java.net.Socket将它们发送到服务器并解析响应的唯一解决方案？

Answer 1

对于高达8的Java版本，以下是我编写的代码，用于在Java中硬编码afoo系统名称DNS解析，以通过测试用例。它的意思是将您的特定条目附加到默认Java运行时DNS解析。

我建议不要在生产中运行它。使用了强制反射访问和Java运行时非公共实现类！

private static final String FOO_IP = "10.10.8.111";

/** Fake "foo" DNS resolution */
@SuppressWarnings("restriction")
public static class MyHostNameService implements sun.net.spi.nameservice.NameService {
    @Override
    public InetAddress[] lookupAllHostAddr(String paramString) throws UnknownHostException {
        if ("foo".equals(paramString) || "foo.domain.tld".equals(paramString)) {
            final byte[] arrayOfByte = sun.net.util.IPAddressUtil.textToNumericFormatV4(FOO_IP);
            final InetAddress address = InetAddress.getByAddress(paramString, arrayOfByte);
            return new InetAddress[] { address };
        } else {
            throw new UnknownHostException();
        }
    }
    @Override
    public String getHostByAddr(byte[] paramArrayOfByte) throws UnknownHostException {
        throw new UnknownHostException();
    }
}

static {
    // Force to load fake hostname resolution for tests to pass
    try {
        List<sun.net.spi.nameservice.NameService> nameServices =
            (List<sun.net.spi.nameservice.NameService>)
            org.apache.commons.lang3.reflect.FieldUtils.readStaticField(InetAddress.class, "nameServices", true);
        nameServices.add(new MyHostNameService());
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
}

希望这有帮助，但再次，小心使用！

Answer 2

具有以下接口并允许访问java。净值*可以将自己的DNS提供程序与JDK8和JDK9一起使用。新的提供者是通过“INameService.install（new MyNameService（））；”安装的

public interface INameService extends InvocationHandler {
    public static void install(final INameService dns) throws IllegalArgumentException, IllegalAccessException, NoSuchFieldException, SecurityException, ClassNotFoundException {
        final Class<?> inetAddressClass = InetAddress.class;
        Object neu;
        Field nameServiceField;
        try {
            final Class<?> iface = Class.forName("java.net.InetAddress$NameService");
            nameServiceField = inetAddressClass.getDeclaredField("nameService");
            neu = Proxy.newProxyInstance(iface.getClassLoader(), new Class<?>[] { iface }, dns);
        } catch(final ClassNotFoundException|NoSuchFieldException e) {
            nameServiceField = inetAddressClass.getDeclaredField("nameServices");
            final Class<?> iface = Class.forName("sun.net.spi.nameservice.NameService");
            neu = Arrays.asList(Proxy.newProxyInstance(iface.getClassLoader(), new Class<?>[] { iface }, dns));
        }
        nameServiceField.setAccessible(true);
        nameServiceField.set(inetAddressClass, neu);
    }

    /**
     * Lookup a host mapping by name. Retrieve the IP addresses associated with a host
     *
     * @param host the specified hostname
     * @return array of IP addresses for the requested host
     * @throws UnknownHostException  if no IP address for the {@code host} could be found
     */
    InetAddress[] lookupAllHostAddr(final String host) throws UnknownHostException;

    /**
     * Lookup the host corresponding to the IP address provided
     *
     * @param addr byte array representing an IP address
     * @return {@code String} representing the host name mapping
     * @throws UnknownHostException
     *             if no host found for the specified IP address
     */
    String getHostByAddr(final byte[] addr) throws UnknownHostException;

    @Override default public Object invoke(final Object proxy, final Method method, final Object[] args) throws Throwable {
        switch(method.getName()) {
        case "lookupAllHostAddr": return lookupAllHostAddr((String)args[0]);
        case "getHostByAddr"    : return getHostByAddr    ((byte[])args[0]);
        default                 :
            final StringBuilder o = new StringBuilder();
            o.append(method.getReturnType().getCanonicalName()+" "+method.getName()+"(");
            final Class<?>[] ps = method.getParameterTypes();
            for(int i=0;i<ps.length;++i) {
                if(i>0) o.append(", ");
                o.append(ps[i].getCanonicalName()).append(" p").append(i);
            }
            o.append(")");
            throw new UnsupportedOperationException(o.toString());
        }
    }
}

Answer 3

Java9删除了此功能。您需要使用第三方DNS客户端库。

如果您使用的是Java 8或更高版本，您可以执行以下操作：

您可以设置本网站记录的系统属性sun.net.spi.nameservice.nameservers。