title: How to use providers in a service?
body: <p>I need use multiple instances of one service.</p>
  
  <p>Usually when I use one instance of this service in component, I write like this:</p>
  
  <pre><code>@Component({
      selector: 'one-component',
      providers: [provide("token1", {useClass: Service})],
      template: `
          &lt;h1&gt;App&lt;/h1&gt;
      `
  })
  export class OneComponent {
      constructor(@Inject('token1') service:Service) {}
  }
  </code></pre>
  
  <p>But now I need use this service in Service2, I write like this:</p>
  
  <pre><code>export class Service2 {
      constructor(@Inject('token1') service:Service) {}
  }
  </code></pre>
  
  <p>As you know, it shows:</p>
  
  <blockquote>
    <p>No provider</p>
  </blockquote>
  
  <p>Because <code>Service2</code> does not have <code>providers: [provide("token1", {useClass: Service})]</code>. But where can I add it since it does not have <code>@Component</code>?</p>
  
  <p>Thanks</p>