HttpClientModule

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.get<Post[]>('/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 | ReadonlyArray<string>;
     };
     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: HttpRequest<unknown>,
    next: HttpHandler
    // unknown 指定响应内容 (body) 的类型
  ): Observable<HttpEvent<unknown>> {
    // 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: HttpRequest<unknown>,
    next: HttpHandler
  ): Observable<any> {
    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
     }
   }
   

   1. /api/*：在应用中发出的以 /api 开头的请求走此代理
   2. target：服务器端 URL
   3. secure：如果服务器端 URL 的协议是 https，此项需要为 true
   4. 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)

   // package.json
   "scripts": {
     "start": "ng serve --proxy-config proxy.conf.json",
   }
   

3. 指定 proxy 配置文件 (方式二)

   // angular.json 文件中
   "serve": {
     "options": {
       "proxyConfig": "proxy.conf.json"
     }
   }