如何在启动angular应用程序时获取第一个http请求的头(http://localhost:4200/)

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';

import { AppComponent } from './app.component';
import { FirstRequestInterceptor } from './interceptors/first-request.interceptor';

@NgModule({
  declarations: [AppComponent],
  imports: [BrowserModule, HttpClientModule],
  providers: [
    {
      provide: HTTP_INTERCEPTORS,
      useClass: FirstRequestInterceptor,
      multi: true
    }
  ],
  bootstrap: [AppComponent]
})
export class AppModule {}

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

@Injectable()
export class FirstRequestInterceptor implements HttpInterceptor {
  private isFirstRequest = true;

  intercept(req: HttpRequest<any>, next: HttpHandler) {
    if (this.isFirstRequest) {
      console.log('First request headers:', req.headers);
      this.isFirstRequest = false;
    }

    return next.handle(req);
  }
}

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-root',
  template: '...'
})
export class AppComponent implements OnInit {
  constructor(private http: HttpClient) {}

  ngOnInit() {
    this.http.get('http://localhost:4200/').subscribe(response => {
      console.log('Response:', response);
    });
  }
}