将多个HTTP拦截器添加到Angular应用程序

Question 1

如何将多个独立的HTTP拦截器添加到Angular 4应用程序？

我试图通过providers使用多个拦截器扩展数组来添加它们。但是只有最后一个被实际执行，才被Interceptor1忽略。

@NgModule({
  declarations: [ /* ... */ ],
  imports: [ /* ... */ HttpModule ],
  providers: [
    {
      provide: Http,
      useFactory: (xhrBackend: XHRBackend, requestOptions: RequestOptions) =>
        new Interceptor1(xhrBackend, requestOptions),
      deps: [XHRBackend, RequestOptions],
    },
    {
      provide: Http,
      useFactory: (xhrBackend: XHRBackend, requestOptions: RequestOptions) =>
        new Interceptor2(xhrBackend, requestOptions),
      deps: [XHRBackend, RequestOptions]
    },
  ],
  bootstrap: [AppComponent]
})
export class AppModule {}

我显然可以将它们合并为一个Interceptor类，并且应该可以工作。但是，我要避免这种情况，因为这些拦截器的用途完全不同（一个用于错误处理，一个用于显示加载指示符）。

那么如何添加多个拦截器？

Question 2

Http不允许有多个自定义实现。但是正如@estus所述，Angular团队最近添加了新的HttpClient服务（版本4.3），该服务支持多个拦截器概念。您无需HttpClient像使用旧版那样扩展Http。您可以HTTP_INTERCEPTORS改为提供一个实现，该实现可以是带有'multi: true'选项的数组：

import {HTTP_INTERCEPTORS, HttpClientModule} from '@angular/common/http';
...

@NgModule({
  ...
  imports: [
    ... ,
    HttpClientModule
  ],
  providers: [
    ... ,
    {
      provide: HTTP_INTERCEPTORS,
      useClass: InterceptorOne,
      multi: true,
    },
    {
      provide: HTTP_INTERCEPTORS,
      useClass: InterceptorTwo,
      multi: true,
    }
  ],
  ...
})

拦截器：

import {HttpEvent, HttpHandler, HttpInterceptor, HttpRequest} from '@angular/common/http';
...

@Injectable()
export class InterceptorOne implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    console.log('InterceptorOne is working');
    return next.handle(req);
  }
}

@Injectable()
export class InterceptorTwo implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    console.log('InterceptorTwo is working');
    return next.handle(req);
  }
}

此服务器调用将打印两个拦截器的日志消息：

import {HttpClient} from '@angular/common/http';
...

@Component({ ... })
export class SomeComponent implements OnInit {

  constructor(private http: HttpClient) {}

  ngOnInit(): void {
    this.http.get('http://some_url').subscribe();
  }
}