1. 建立一个 class类HttpRequestInterceptor，实现 HttpInterceptor重写 intercept，代码如下

import {Injectable} from '@angular/core';
import {HttpEvent, HttpHandler, HttpInterceptor, HttpRequest, HttpResponse} from '@angular/common/http';
import {Observable} from 'rxjs';
import {tap} from 'rxjs/operators';
import {Router} from '@angular/router';@Injectable()
export class HttpRequestInterceptor implements HttpInterceptor {constructor(private router: Router) {}intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {if (req.url.endsWith('login')) {return next.handle(req).pipe(tap(event => {if (event instanceof HttpResponse) {}}, e => {if (e.status === 401) {alert('用户名或密码错误');}}));}const modifiedReq = req.clone({// 在header中添加tokensetHeaders: {Authorization: 'Bearer ' + localStorage.getItem('access_token')}});const _this = this;return next.handle(modifiedReq).pipe(tap(event => {if (event instanceof HttpResponse) {console.log(event);}}, e => {console.log(e);if (e.status === 401) {_this.router.navigateByUrl('/login');}}));}}

2. 在 app.module.ts的providers添加

{provide: HTTP_INTERCEPTORS, useClass: HttpRequestInterceptor, multi: true}