title: Rxjava with Retrofit save emit data in file in background
body: <p>I am very new to Rxjava and RetroFit. I have one issue . </p>
  
  <p>I am fetching data from server with below code.</p>
  
  <pre><code> ApiUtils.getMainRestService(mContext).getMain(url).
              subscribeOn(Schedulers.newThread()).observeOn(AndroidSchedulers.mainThread()).
              subscribe(new Action1&lt;CMSMain&gt;() {
                  @Override
                  public void call(CMSMain CMSMain) {
  
                  }
              });
  </code></pre>
  
  <p>Now i want to save this CMSMain into file in background . How can i do this.
  yes i can use Schedular.newThread() inside observerOn method after that which method will call in UI thread.</p>