Angular 4如何为整个应用程序设置HttpClient的默认选项？

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

@Injectable()
export class HttpInterceptorService implements HttpInterceptor {
  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    // 在这里可以修改请求的默认选项
    const modifiedRequest = request.clone({
      // 设置默认的请求头
      setHeaders: {
        'Content-Type': 'application/json'
      },
      // 设置默认的请求参数
      params: request.params.set('key', 'value')
    });

    // 继续处理修改后的请求
    return next.handle(modifiedRequest);
  }
}

import { NgModule } from '@angular/core';
import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';
import { HttpInterceptorService } from './http-interceptor.service';

@NgModule({
  imports: [
    HttpClientModule
  ],
  providers: [
    {
      provide: HTTP_INTERCEPTORS,
      useClass: HttpInterceptorService,
      multi: true
    }
  ]
})
export class AppModule { }