Angular的拦截器可以用来截获HTTP请求并对其进行处理。在应用程序中，我们可以使用拦截器来显示加载指示器或以某种方式修改请求。下面是一些使用拦截器的代码示例。

1. 创建一个加载拦截器

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

@Injectable()
export class LoadingInterceptor implements HttpInterceptor {

  constructor(private loadingService: LoadingService) {}

  intercept(request: HttpRequest, next: HttpHandler): Observable> {
    this.loadingService.show();
    return next.handle(request).pipe(
      finalize(() => this.loadingService.hide())
    );
  }

}

2. 在模块提供器中注册拦截器

import { NgModule } from '@angular/core';
import { HTTP_INTERCEPTORS } from '@angular/common/http';
import { LoadingInterceptor } from './loading.interceptor';

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

3. 创建一个加载服务来显示和隐藏加载指示器

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root',
})
export class LoadingService {
  loading = false;

  show() {
    this.loading = true;
  }

  hide() {
    this.loading = false;
  }
}

4. 在需要展示加载指示器的组件中添加HTML模板代码