@Injectable()
export class ProductListResolverService implements Resolve<Product>{
 
    constructor(private productService:ProductService ) {
    }
 
    resolve(route: ActivatedRouteSnapshot,
            state: RouterStateSnapshot): Observable<any> {
 
        console.log("ProductListResover is called");
        return this.productService.getProducts();
    }
 
}

// the component that uses the resolver: 
 ngOnInit() {
      this.products=this.route.snapshot.data['products'];
   }

//the routing module 

{ path: 'product', component: ProductComponent, 
    resolve: {products: ProductListResolveService, , data:SomeOtherResolverService}  }