title: REST calling is double executed at the time of multistep execution of Observable.subscribe
body: <p>Application is using Angular 2.4.3.
  The problem that a REST calling is double executed by once in 2-3 months at present occurs.
  Please tell me solution method.</p>
  
  <p>The <strong>flow of processing</strong> is as follows.</p>
  
  <p>(1) a button is clicked.</p>
  
  <p>(2) <code>REST1</code> is executed.</p>
  
  <p>(3) when ResponseStatus of <code>REST1</code> was <code>200</code>, <code>REST2</code> is executed.</p>
  
  <p><strong>above-mentioned (3) <code>REST2</code> is double executed</strong>.</p>
  
  <p>It's double executed by log of <code>RESTService</code> the same time.</p>
  
  <p>The <strong>sample code</strong> is as follows.
  I'm doing multistep execution of <code>Observable.subscribe</code>, but are there any problems in the code contents?</p>
  
  <pre><code>// (2) execution of REST1
  let observable: Observable&lt;Response&gt; = this.http.get(requestOptions);
  observable.subscribe((response: Response) =&gt; {
      let responseData: any = response.response.json();
  
      if (200 === response.status) {
          no1 = responseData.xxx.no1;
          no2 = responseData.xxx.no2;
          no3 = responseData.xxx.no2;
  
          // Abbreviation
  
          let requestOptions: RequestOptions = new RequestOptions({
              headers: headerParameters,
              search: urlParameters
          });
          let body = {
              "no1": no1,
              "no2": no2,
              "no3": no3,
          };
          let xxxDaoData: XxxDaoData = new XxxDaoData();
          xxxDaoData.data = body;
  
          // (3) execution of REST2 (REST is double executed)
          let observable2: Observable&lt;Response&gt; = this.http.post(xxxDaoData, requestOptions);
          observable2.subscribe((response: Response) =&gt; {
              // Abbreviation
          }
      }
  }
  </code></pre>
  
  <p>If there are bug information on Angular and a case, please tell me.</p>