我一直在尝试连接我的后端（spring boot/java）和前端（angular），但我一直在控制台中得到这个错误：

error: SyntaxError: Unexpected token 'S', "[Services {"... is not valid JSON at JSON.parse,
message: "Http failure during parsing for http://localhost:8080/providers/getServices"

我的服务看起来像这样：

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Observable } from 'rxjs';

import { ServiceSection } from 'src/app/models/services/service-section';

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

  private servicesUrl: string;
  private projectsUrl: string;
  // services: Observable<ServiceSection[]>;

  constructor(private http: HttpClient) {
    this.servicesUrl = 'http://localhost:8080/providers/getServices';
    this.projectsUrl = 'http://localhost:8080/projects/getAllProjects'
  }

  public getAll(): Observable<ServiceSection[]> {
    console.log(this);
    return this.http.get<ServiceSection[]>(this.servicesUrl);
  }
}

我的控制器是这样的：

package hibera.web.api.controllers;

import com.google.api.core.ApiFuture;
import com.google.cloud.firestore.CollectionReference;
import com.google.cloud.firestore.DocumentSnapshot;
import com.google.cloud.firestore.QuerySnapshot;
import hibera.web.api.domain.Services;
import hibera.web.api.service.FirebaseInit;
import hibera.web.api.service.ProvidingsService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;

@RestController
@RequestMapping("/providers")
@CrossOrigin(origins = "http://localhost:4200")
public class ProvidersController {
    @Autowired
    FirebaseInit db;
    @Autowired
    public ProvidingsService service;

    @GetMapping("/getServices")
    public String getServices() throws InterruptedException, ExecutionException {
        List<Services> services = new ArrayList<Services>();

        CollectionReference service = db.getFirebase().collection("services_section");
        ApiFuture<QuerySnapshot> querySnapshot = service.get();

        for (DocumentSnapshot doc:querySnapshot.get().getDocuments()){
            Services serv = doc.toObject(Services.class);
            services.add(serv);
        }

        return services.toString();
    }
}

我知道它没有被解析为一个json对象，但是当我尝试添加{responseType: 'text'}时，它在控制台中给了我一堆错误。在postman中一切都很好，但是尝试将数据从数据库循环到客户端让我非常头痛。老实说，我认为这与API无关，而是与客户端有关。
如果有人能给我答案或者至少帮我。
提前感谢：）