title: Access a service from a custom validator in Angular2
body: <p>I need to access my custom http service from inside a static method, as example:</p>
  
  <pre><code>import {Control} from 'angular2/common';
  import {HttpService} from './http.service';
  
  class UsernameValidator {
      static usernameExist(control: Control): Promise&lt;ValidationResult&gt; { 
          ... /* Access my HTTPservice here */
      }
  }
  </code></pre>
  
  <p>How can I access a service in this case?</p>