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Angular自带有http模块可以方便的进行Http请求。不必像Vue那样安装配置axios。

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

@Component({
  selector: 'app-root',
  templateUrl: 'app/app.component.html'
})
export class AppComponent {

  constructor(private http: HttpClient) { }
  
  ngOnInit() {
    // 发起一个get请求
    this.http.get('/api/people/1').subscribe(json => console.log(json));
  }
}
import { Component } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-root',
  templateUrl: 'app/app.component.html'
})
export class AppComponent {

  constructor(private http: HttpClient) { }
  
  ngOnInit() {
    // 发起一个get请求
    this.http.get('/api/people/1').subscribe(json => console.log(json));
  }
}

注意:上面的this.http.get... 处理HTTP最好放到单独的Service文件中,再注入到Component。这里为了演示没有这么做。

优化有顺序依赖的多个请求

有些时候我们需要按顺序发起多个请求,根据第一个请求返回的结果中的某些内容,作为第二个请求的参数,比如下面代码。

javascript
  ngOnInit() {
    this.http.get('/api/people/1').subscribe(character => {
      this.http.get(character.id).subscribe(homeworld => {
        character.homeworld = homeworld;
        this.loadedCharacter = character;
      });
    });
  }
  ngOnInit() {
    this.http.get('/api/people/1').subscribe(character => {
      this.http.get(character.id).subscribe(homeworld => {
        character.homeworld = homeworld;
        this.loadedCharacter = character;
      });
    });
  }

上面的嵌套写法可读性不那么好,我们可以使用RxJS提供的mergeMap操作符来优化上述代码

typescript
import { Component } from '@angular/core';
import { Http } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import { mergeMap } from 'rxjs/operators';

@Component({
  selector: 'app-root',
  templateUrl: 'app/app.component.html'
})
export class AppComponent {
  homeworld: Observable<{}>;
  constructor(private http: HttpClient) { }
  
  ngOnInit() {
    this.homeworld = this.http.get('/api/people/1')
    .pipe(
      mergeMap(character => this.http.get(character.homeworld))
    );
  }
}
import { Component } from '@angular/core';
import { Http } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import { mergeMap } from 'rxjs/operators';

@Component({
  selector: 'app-root',
  templateUrl: 'app/app.component.html'
})
export class AppComponent {
  homeworld: Observable<{}>;
  constructor(private http: HttpClient) { }
  
  ngOnInit() {
    this.homeworld = this.http.get('/api/people/1')
    .pipe(
      mergeMap(character => this.http.get(character.homeworld))
    );
  }
}

mergeMap 操作符用于从内部的 Observable 对象中获取值,然后返回给父级流对象。 可以合并 Observable 对象

处理并发请求

forkJoin 是 Rx 版本的 Promise.all(),即表示等到所有的 Observable 都完成后,才一次性返回值。

typescript
import { Component } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import { forkJoin } from "rxjs/observable/forkJoin";

@Component({
  selector: 'app-root',
  templateUrl: 'app/app.component.html'
})
export class AppComponent {
  loadedCharacter: {};
  constructor(private http: HttpClient) { }
  
  ngOnInit() {
    let character = this.http.get('https://swapi.co/api/people/1');
    let characterHomeworld = this.http.get('http://swapi.co/api/planets/1');

    forkJoin([character, characterHomeworld]).subscribe(results => {
      // results[0] is our character
      // results[1] is our character homeworld
      results[0].homeworld = results[1];
      this.loadedCharacter = results[0];
    });
  }
}
import { Component } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import { forkJoin } from "rxjs/observable/forkJoin";

@Component({
  selector: 'app-root',
  templateUrl: 'app/app.component.html'
})
export class AppComponent {
  loadedCharacter: {};
  constructor(private http: HttpClient) { }
  
  ngOnInit() {
    let character = this.http.get('https://swapi.co/api/people/1');
    let characterHomeworld = this.http.get('http://swapi.co/api/planets/1');

    forkJoin([character, characterHomeworld]).subscribe(results => {
      // results[0] is our character
      // results[1] is our character homeworld
      results[0].homeworld = results[1];
      this.loadedCharacter = results[0];
    });
  }
}

在线演示

错误处理请求

使用 catchError 处理observable中的错误,需要返回一个新的 observable 或者直接抛出error

例1 ,在请求方法内部处理错误,若请求失败返回一个默认值,看起来用户也感知不到发生了错误

typescript
  // http.service.ts
  getPostDetail(id) {
    return this.http
    .get<any>(`https://jsonplaceholder.typicode.com/posts/${id}`)
      .pipe(
        // catchError 需要 returning a new observable or throwing an error.
        catchError(err => {
          // 如果发生错误,用缺省值,(尝试修改为错误地址)
          return of({
            userId: 1,
            id: 1,
            title: '-occaecati excepturi optio reprehenderit-',
            body: '-eveniet architecto-'
          });
        })
    )
  }
  // component 中调用
  getPostDetail() {
    this.postDetail$ = this.service.getPostDetail(1)
    .subscribe(val => {
      console.log(val);
    });
  }
  // http.service.ts
  getPostDetail(id) {
    return this.http
    .get<any>(`https://jsonplaceholder.typicode.com/posts/${id}`)
      .pipe(
        // catchError 需要 returning a new observable or throwing an error.
        catchError(err => {
          // 如果发生错误,用缺省值,(尝试修改为错误地址)
          return of({
            userId: 1,
            id: 1,
            title: '-occaecati excepturi optio reprehenderit-',
            body: '-eveniet architecto-'
          });
        })
    )
  }
  // component 中调用
  getPostDetail() {
    this.postDetail$ = this.service.getPostDetail(1)
    .subscribe(val => {
      console.log(val);
    });
  }

例2 直接把错误抛出来,在外部处理错误,比如来个弹窗,提示告诉用户

typescript
  getPostDetail(id) {
    return this.http
    .get<any>(`${this.endpoint}/posts2/${id}`)
      .pipe(
        // catchError  returning a new observable or throwing an error.
        catchError(err => {
          throw err;
        })
      )
  }

// 改造调用方法
  getPostDetail() {
    this.postDetail$ = this.service.getPostDetail(1)
      .subscribe(
        (next) => {
        },  
       // 这里接收内部抛出的错误
        err => {
          // 可以加入自己的错误处理逻辑,搞个弹窗,notify等
          console.log(err);
        }
      )
  }
  getPostDetail(id) {
    return this.http
    .get<any>(`${this.endpoint}/posts2/${id}`)
      .pipe(
        // catchError  returning a new observable or throwing an error.
        catchError(err => {
          throw err;
        })
      )
  }

// 改造调用方法
  getPostDetail() {
    this.postDetail$ = this.service.getPostDetail(1)
      .subscribe(
        (next) => {
        },  
       // 这里接收内部抛出的错误
        err => {
          // 可以加入自己的错误处理逻辑,搞个弹窗,notify等
          console.log(err);
        }
      )
  }

参考

使用 RxJS 处理多个 Http 请求