该模块用于发送 Http 请求，用于发送请求的方法都返回 Observable 对象。

1、快速开始

1）、引入 HttpClientModule 模块

// app.module.ts
import {
 httpClientModule }
     from '@angular/common/http';

imports: [
  httpClientModule
]

2）、注入 HttpClient 服务实例对象，用于发送请求

// app.component.ts
import {
 HttpClient }
     from '@angular/common/http';


export class AppComponent {

	constructor(private http: HttpClient) {
}

}

3）、发送请求

import {
 HttpClient }
 from "@angular/common/http"

export class AppComponent implements OnInit {

  constructor(private http: HttpClient) {
}

  ngOnInit() {

    this.getUsers().subscribe(console.log)
  }

  getUsers() {

    return this.http.get("https://jsonplaceholder.typicode.com/users")
  }

}
    

2、请求方法

this.http.get(url [, options]);
    
this.http.post(url, data [, options]);
    
this.http.delete(url [, options]);
    
this.http.put(url, data [, options]);
    

this.http.getPost[]>
    ('/getAllPosts')
  .subscribe(response =>
 console.log(response))

3、请求参数

1、HttpParams 类

export declare class HttpParams {
    
    constructor(options?: HttpParamsOptions);
    
    has(param: string): boolean;
    
    get(param: string): string | null;
    
    getAll(param: string): string[] | null;
    
    keys(): string[];
    
    append(param: string, value: string): HttpParams;
    
    set(param: string, value: string): HttpParams;
    
    delete(param: string, value?: string): HttpParams;
    
    toString(): string;

}

2、HttpParamsOptions 接口

declare interface HttpParamsOptions {
    
    fromString?: string;

    fromObject?: {
    
        [param: string]: string | ReadonlyArraystring>
    ;

    }
    ;
    
    encoder?: HttpParameterCodec;

}

3、使用示例

import {
 HttpParams }
     from '@angular/common/http';


let params = new HttpParams({
 fromObject: {
name: "zhangsan", age: "20"}
}
)
params = params.append("sex", "male")
let params = new HttpParams({
     fromString: "name=zhangsan&
age=20"}
)

4、请求头

请求头字段的创建需要使用 HttpHeaders 类，在类实例对象下面有各种操作请求头的方法。

export declare class HttpHeaders {

    constructor(headers?: string | {
    
        [name: string]: string | string[];

    }
    );
    
    has(name: string): boolean;
    
    get(name: string): string | null;
    
    keys(): string[];
    
    getAll(name: string): string[] | null;
    
    append(name: string, value: string | string[]): HttpHeaders;
    
    set(name: string, value: string | string[]): HttpHeaders;
    
    delete(name: string, value?: string | string[]): HttpHeaders;

}

let headers = new HttpHeaders({
 test: "Hello" }
    )

5、响应内容

declare type HttpObserve = 'body' | 'response';

// response 读取完整响应体
// body 读取服务器端返回的数据

this.http.get(
  "https://jsonplaceholder.typicode.com/users", 
  {
 observe: "body" }
    
).subscribe(console.log)

6、拦截器

拦截器是 Angular 应用中全局捕获和修改 HTTP 请求和响应的方式。（Token、Error）

拦截器将只拦截使用 HttpClientModule 模块发出的请求。

ng g interceptor name>

6.1 请求拦截

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

  constructor() {
}
    
	// 拦截方法
  intercept(
  	// unknown 指定请求体 (body) 的类型
    request: HttpRequestunknown>
    ,
    next: HttpHandler
     // unknown 指定响应内容 (body) 的类型
  ): ObservableHttpEventunknown>
    >
 {

    // 克隆并修改请求头
    const req = request.clone({

      setHeaders: {

        Authorization: "Bearer xxxxxxx"
      }

    }
)
    // 通过回调函数将修改后的请求头回传给应用
    return next.handle(req)
  }

}

6.2 响应拦截

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

  constructor() {
}
    
	// 拦截方法
  intercept(
    request: HttpRequestunknown>
    ,
    next: HttpHandler
  ): Observableany>
 {
    
    return next.handle(request).pipe(
      retry(2),
      catchError((error: HttpErrorResponse) =>
 throwError(error))
    )
  }

}

6.3 拦截器注入

import {
 AuthInterceptor }
 from "./auth.interceptor"
import {
 HTTP_INTERCEPTORS }
 from "@angular/common/http"

@NgModule({

  providers: [
    {

      provide: HTTP_INTERCEPTORS,
      useClass: AuthInterceptor,
      multi: true
    }

  ]
}
)

7、Angular Proxy

1、在项目的根目录下创建 proxy.conf.json 文件并加入如下代码

{

 	"/api/*": {

    "target": "http://localhost:3070",
    "secure": false,
    "changeOrigin": true
  }

}

• /api/*：在应用中发出的以 /api 开头的请求走此代理

• target：服务器端 URL

• secure：如果服务器端 URL 的协议是 https，此项需要为 true

• changeOrigin：如果服务器端不是 localhost， 此项需要为 true

2、指定 proxy 配置文件 (方式一)

"scripts": {

  "start": "ng serve --proxy-config proxy.conf.json",
}

3、指定 proxy 配置文件 (方式二)

"serve": {

  "options": {

    "proxyConfig": "proxy.conf.json"
  }
    ,

该模块用于发送 Http 请求，用于发送请求的方法都返回 Observable 对象。