(Java) Revert to Default DNS Nameservers

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Demonstrates how to revert back to the default nameservers of the local system where your application is running.

Note: This example requires Chilkat v9.5.0.96 or later.

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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // The only reason you would have to revert back to the local system's default nameservers
    // is if your application had previously set different nameservers, and you wish to revert back.

    // When your application starts, the DNS nameservers to be used are the default nameservers
    // configured on the system where your application is running.

    // There is one exception: Chilkat defaults to using the public Google nameservers (8.8.8.8 and 8.8.4.4) for
    // Android applications. Reverting to the default nameservers would revert to the Google nameservers.

    // However, Chilkat does not query the local system for the default nameservers unless Chilkat needs
    // to do a DNS lookup and there not yet any DNS nameservers defined.  Thus technically, when your application
    // starts, there are no default nameservers. They are auto-assigned when first needed.

    // If your application explicitly defines DNS nameservers, such as by calling AddDefaultnamervers, or AddNameserver
    // then Chilkat will not automatically auto-assign.

    CkDns dns = new CkDns();

    // Here we are explicitly adding the system default nameservers, because technically this application
    // has not yet done anything that would require a DNS lookup, and thus DNS nameservers are not yet defined.
    // Your default nameserver is assumed to not support TLS.
    dns.AddDefaultNameservers();

    // Let's examine our nameservers
    int nsCount = dns.get_NumNameservers();
    int i = 0;
    while (i < nsCount) {
        System.out.println((i+1) + ": " + dns.getNameserver(i));
        i = i+1;
        }

    // On my Windows system, the result is a single nameserver at 
    // 1: 172.16.16.16

    // ---------------------------------------------------------
    // We could add additional nameservers, such as Google and Cloudfare
    boolean supportsTls = true;
    // Cloudfare
    dns.AddNameserver("1.1.1.1",supportsTls);
    // Google
    dns.AddNameserver("8.8.8.8",supportsTls);

    // See the nameservers now used by Chilkat
    nsCount = dns.get_NumNameservers();
    i = 0;
    while (i < nsCount) {
        System.out.println((i+1) + ": " + dns.getNameserver(i));
        i = i+1;
        }

    // Result:
    // 1: 172.16.16.16
    // 2: 1.1.1.1
    // 3: 8.8.8.8

    // ---------------------------------------------------------
    // To revert back to the system default nameservers, clear all
    // then re-add the default.
    dns.RemoveAllNameservers();
    dns.AddDefaultNameservers();

    // See the nameservers now used by Chilkat
    nsCount = dns.get_NumNameservers();
    i = 0;
    while (i < nsCount) {
        System.out.println((i+1) + ": " + dns.getNameserver(i));
        i = i+1;
        }

    // Result:
    // 1: 172.16.16.16
  }
}