新的HttpHeader类的实例是不可变对象。调用类方法将返回一个新实例作为结果。所以基本上，你需要做以下事情:

let headers = new HttpHeaders();
headers = headers.set('Content-Type', 'application/json; charset=utf-8');

or

const headers = new HttpHeaders({'Content-Type':'application/json; charset=utf-8'});

更新:增加多个报头

let headers = new HttpHeaders();
headers = headers.set('h1', 'v1').set('h2','v2');

or

const headers = new HttpHeaders({'h1':'v1','h2':'v2'});

更新:接受HttpClient头和参数的对象映射

因为5.0.0-beta。现在可以跳过HttpHeaders对象的创建，直接传递一个对象映射作为参数。所以现在可以做以下事情:

http.get('someurl',{
   headers: {'header1':'value1','header2':'value2'}
});

我用的是Angular 8，唯一对我有用的是:

  getCustomHeaders(): HttpHeaders {
    const headers = new HttpHeaders()
      .set('Content-Type', 'application/json')
      .set('Api-Key', 'xxx');
    return headers;
  }

在HTTP请求中像下面这样设置HTTP报头

return this.http.get(url, { headers: new HttpHeaders({'Authorization': 'Bearer ' + token})
 });

要添加多个参数或头，您可以执行以下操作:

constructor(private _http: HttpClient) {}

//....

const url = `${environment.APP_API}/api/request`;

let headers = new HttpHeaders().set('header1', hvalue1); // create header object
headers = headers.append('header2', hvalue2); // add a new header, creating a new object
headers = headers.append('header3', hvalue3); // add another header

let params = new HttpParams().set('param1', value1); // create params object
params = params.append('param2', value2); // add a new param, creating a new object
params = params.append('param3', value3); // add another param 

return this._http.get<any[]>(url, { headers: headers, params: params })

带有错误处理和自定义报头的Angular 8 HttpClient服务示例

    import { Injectable } from '@angular/core';
    import { HttpClient, HttpHeaders, HttpErrorResponse } from '@angular/common/http';
    import { Student } from '../model/student';
    import { Observable, throwError } from 'rxjs';
    import { retry, catchError } from 'rxjs/operators';

    @Injectable({
      providedIn: 'root'
    })
    export class ApiService {

      // API path
      base_path = 'http://localhost:3000/students';

      constructor(private http: HttpClient) { }

      // Http Options
      httpOptions = {
        headers: new HttpHeaders({
          'Content-Type': 'application/json'
        })
      }

      // Handle API errors
      handleError(error: HttpErrorResponse) {
        if (error.error instanceof ErrorEvent) {
          // A client-side or network error occurred. Handle it accordingly.
          console.error('An error occurred:', error.error.message);
        } else {
          // The backend returned an unsuccessful response code.
          // The response body may contain clues as to what went wrong,
          console.error(
            `Backend returned code ${error.status}, ` +
            `body was: ${error.error}`);
        }
        // return an observable with a user-facing error message
        return throwError(
          'Something bad happened; please try again later.');
      };


      // Create a new item
      createItem(item): Observable<Student> {
        return this.http
          .post<Student>(this.base_path, JSON.stringify(item), this.httpOptions)
          .pipe(
            retry(2),
            catchError(this.handleError)
          )
      }

      ....
      ....

点击这里查看完整的示例教程

我也在和这个斗争。我使用了一个拦截器，它捕获响应头，然后克隆头(因为头是不可变的对象)，然后发送修改后的头。https://angular.io/guide/http#intercepting-requests-and-responses