使用http.post

Question

我写过（从SO复制！）以下拦截器代码。我想修改传出请求并拦截响应。但是，我注意到响应永远不会被截获。为什么？是因为我使用的是Rxjs吗？

拦截器代码

import {HttpEvent, HttpHandler, HttpInterceptor, HttpRequest, HttpResponse} from "@angular/common/http";
import {Injectable} from "@angular/core";
import {Observable} from "rxjs/Observable";
import 'rxjs/add/operator/do';

@Injectable()
export class CustomInterceptor implements HttpInterceptor {

  constructor() {
  }

  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

    console.log("outgoing request",request);
    request = request.clone({
      withCredentials: true
    });
    console.log("new outgoing request",request);

    return next
      .handle(request)
      .do((ev: HttpEvent<any>) => {
        if (ev instanceof HttpResponse) {
          console.log('processing response', ev);  //I DON'T SEE THIS PRINT
        }
      });
  }
}

我将请求发送到服务器，如下所示

 return this.http.post(/*this.API_URL+*/this.SIGNIN_USER_URL,body,httpOptions)
      .map(response=>{
        console.log('response from backend service',response); //I SEE THIS PRINT
        let result= <ServerResponse>response; 
        console.log("result is "+result.result+' with additional information '+result.additionalInformation)
        return result;
      })
  .catch(this.handleError);

为什么拦截器代码没有被击中？

更新 - app.module.ts

中的提供商代码段

providers: [WebToBackendInterfaceService, //some other provider
    {
      provide: HTTP_INTERCEPTORS,
      useClass: CustomInterceptor , //interceptor provider
      multi: true
    }],

我在do和if之间添加了一个打印件（console.log("got an event",ev)。我可以在控制台上看到以下消息`有一个事件

{…}
​body: Object { result: "success", "additional-info": "found user" }
​headers: {…}
​lazyInit: function lazyInit()
​​lazyUpdate: null
​​normalizedNames: Map
​​​size: 0
​​​<entries>
​​​__proto__: Object { … }
​​__proto__: Object { has: has(), get: get(), keys: keys(), … }
​ok: true
​status: 200
​statusText: "OK"
​type: 4
​url: "http://localhost:9000/ws/users/signin"
​__proto__: Object { constructor: HttpResponse(), clone: clone() }`

我不知道为什么if语句没有被执行，因为事件似乎是HttpResponse类型（指​__proto__: Object { constructor: HttpResponse(), clone: clone() }）