theotherian/thread-local-dns

Alternative DNS implementation that supports overriding DNS lookups within the scope of an inheritable thread local value

So how do I use this thing?

I'm so glad you asked!

There are three points of entry into this API: initialization, execution and configuration.

Initialization

First and foremost, you absolutely must call ThreadLocalDns.initialize() in your application before any DNS lookups are performed within your JVM instance. If you fail to do this, then Java will initialize the default DNS implementation and you won't be able to override anything at runtime.

Execution

This is your main point of access for using the API. In order to work with solutions that spawn thread pools (for instance, a proxy server), thread-local-dns provides overridden DNS settings in an InheritableThreadLocal. As a result, you'll need to provide a context of what you want to run within that scope.

The code you need to write looks like this:

ThreadLocalDns.executeContext(dnsConfiguration, new ThreadLocalDnsContext() {
  public void execute() {
    // your code goes here
  }
});

Configuration

In order to create the dnsConfiguration argument, you should use DnsConfigurationBuilder by importing it statically.

...
import static com.theotherian.dns.DnsConfigurationBuilder.*
...

public class MyApplication {

  ...

  public void doSomething() {
    ThreadLocalDnsConfiguration dnsConfiguration = newBuilder().map(hosts("www.somehost.com", "www.someotherhost.com"),
      to("127.0.0.1")).map(hosts("www.anotherhost.org"), to("127.0.0.2")).build();
    ...
    ThreadLocalDns.executeContext(dnsConfiguration, new ThreadLocalDnsContext() {
      public void execute() {
        // your code goes here
      }
    });
  }

  ...

}