在Angular2中调用多个相关的Http调用

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { switchMap } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class DataService {
  constructor(private http: HttpClient) {}

  fetchData() {
    return this.http.get('api/endpoint1').pipe(
      switchMap(response1 => {
        // 使用response1的数据发起下一个请求
        return this.http.get(`api/endpoint2?param=${response1.someValue}`);
      })
    );
  }
}

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { forkJoin } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class DataService {
  constructor(private http: HttpClient) {}

  fetchMultipleData() {
    const request1 = this.http.get('api/endpoint1');
    const request2 = this.http.get('api/endpoint2');
    const request3 = this.http.get('api/endpoint3');

    return forkJoin([request1, request2, request3]);
  }
}

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { catchError } from 'rxjs/operators';
import { of } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class DataService {
  constructor(private http: HttpClient) {}

  fetchData() {
    return this.http.get('api/endpoint').pipe(
      catchError(error => {
        console.error('An error occurred:', error);
        return of(null); // 返回一个空值或其他默认值
      })
    );
  }
}