angular 2 cache http responses

ng2-http-cache.service.ts

import {Injectable} from '@angular/core';
import {Http, Headers} from '@angular/http';
import {Observable} from 'rxjs/Observable';
import 'rxjs/observable/of';
import 'rxjs/add/operator/share';
import 'rxjs/add/operator/map';
import {Data} from './data';

@Injectable()
export class DataService {
  private url:string = 'https://cors-test.appspot.com/test';
  
  private data;
  private observable: Observable;

  constructor(private http:Http) {}

  getData() {
    console.log('getData called');
    if(this.data) {
      return Observable.of(this.data); 
    } else if(this.observable) {
      return this.observable;
    } else {
      console.log('send new request');
      let headers = new Headers();
      headers.append('Content-Type', 'application/json');
      this.observable = this.http.get(this.url, {
        headers: headers
      })
      .map(response =>  {
        console.log('response arrived');
        this.observable = null;

        if(response.status == 400) {
          return "FAILURE";
        } else if(response.status == 200) {
          this.data = response.json();
          return this.data;
        }
        // make it shared so more than one subscriber can get the result
      })
      .share();
      return this.observable;
    }
  }
}