Angular2可观察的份额不起作用

BuildingService.ts

@Injectable()
export class BuildingService {

constructor(private http: Http){       
  }

buildings$: Observable<Building[]>;
this.buildings: Building[];

getData() : Observable<Building[]>{
     this.buildings$= this.http.get('http://localhost:8080/buildings').share().map(this.extractData);
     this.buildings$.subscribe(buildings => this.buildings = buildings);
     return this.buildings$;
  }

 private extractData(res: Response) {
    let body = res.json();
    return body;
} 

}

component1.ts

export class component1 {
constructor( private  buildingService: BuildingService) {}

this.subscription = this.buildingService.getData()
            .subscribe(buildings => console.log(buildings),error =>  this.errorMessage = <any>error);
}

component2.ts

export class component2 {
constructor( private  buildingService: BuildingService) {}

this.subscription = this.buildingService.getData()
            .subscribe(buildings => console.log(buildings),error =>  this.errorMessage = <any>error);
}

分享不起作用,多个http呼叫正在进行.即使我尝试了this link的代码

但没用

有人可以告诉我如何使用Angular Observable避免重复的http调用吗？