前端analysis | What,Why,Who,When,Where,How

《angular8》- Angular HttpClient 30分钟轻松上手

2020-06-12

Angular8 HttpClient 30分钟深入了解下

前端开发，axios是标配的http请求发起libary, 采用的是Promise的方式。然后，Angular中采用的是另外一种形式Observable，观察订阅模式。Angular默认推荐采用内置的HTTPClient。
下面让我们开始今天的主题，HTTPClient

模块引入

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

@NgModule({
    declarations: [
        AppComponent
    ],
    imports: [
        BrowserModule,
        HttpClientModule
    ],
    providers: [],
    bootstrap: [AppComponent]
})
export class AppModule {
}

入门

GET请求

指定请求返回类型
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this.http.get<Config>(this.configUrl)
  .subscribe((data: Config) => this.config = { ...data });
  • get请求，明确返回的数据类型为Config,故请求形式为：
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    this.http.get<Config>()...
  • 请求返回后，进行数据转换
不指定请求返回类型
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this.http.get(this.configUrl)
.subscribe((data: any) => this.config = { ...data });

等效于

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this.http.get<Object>(this.configUrl)
.subscribe((data: Object) => this.config = { ...data });

问题1： 如果服务端，返回的数据就是一个text文本，譬如Hello,world，你猜会怎么样？

请求url携带参数
  • 方法一：HttpParams 形式set 
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    # 必须.链式set，否则参数空
    const params = new HttpParams()
        .set('orderBy', '"$key"')
        .set('limitToFirst', "1");
        
    this.http.get(this.configUrl,{params})
      .subscribe((data: any) => this.config = { ...data });
  • 方法二： fromString
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    const params = new HttpParams({
      fromString: 'orderBy="$key"&limitToFirst=1'
    });

    this.http.get(this.configUrl,{params})
        .subscribe((data: any) => this.config = { ...data });
    问题2： 如果前端想拿到后端api header头中参数，怎么办？

POST

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this.http.post(url,
    {
        "courseListIcon": "...",
        "description": "TEST",
        "iconUrl": "..",
        "longDescription": "...",
        "url": "new-url"
    })
    .subscribe(
        (res) => {
            console.log("POST call successful value returned in body", 
                        res);
        },
        error => {
            console.log("POST call in error", error);
        },
        () => {
            console.log("The POST observable is now completed.");
        });
}

DELETE

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this.http.delete(url1)
    .subscribe(
        (res) => {
            console.log("DELETE call successful value returned in body", 
                        res);
        },
        error => {
            console.log("DELETE call in error", error);
        },
        () => {
            console.log("The DELETE observable is now completed.");
        });
}

PATCH

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this.http.patch(url,
    {
        "description": "Angular Tutorial For Beginners PATCH TEST",
    })
    .subscribe(
        (res) => {
            console.log("PATCH call successful value returned in body", 
                        res);
        },
        error => {
            console.log("PATCH call in error", error);
        },
        () => {
            console.log("The PATCH observable is now completed.");
        });
}

进阶

GET请求

request方式传参
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   const params = new HttpParams({
    fromString: 'orderBy="$key"&limitToFirst=1'
});

this.http.request("GET",this.configUrl, { params })
header传参
  • 方法一： HttpHeaders 
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     const headers = new HttpHeaders()
              .set("X-CustomHeader", "custom header value");
              
    this.http.get(this.configUrl,{ headers })
      .do(console.log)
      .map(data => _.values(data));
  • 方法二：{} 字面量 
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     const headers = {
       "X-CustomHeader", "custom header value",
       'content-type': 'application/json'
     }
     
    this.http.get(this.configUrl,{ headers })
      .do(console.log)
      .map(data => _.values(data));
解答问题1：

  • 我们看一下源码针对Get方法请求参数的定义

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    get(url: string, options?: {
          headers?: HttpHeaders | {
              [header: string]: string | string[];
          };
          
          # 默认值有： response| body| event 
          observe?: 'body';# 默认读取的是response中的body 
          params?: HttpParams | {
              [param: string]: string | string[];
          };
          reportProgress?: boolean;
          
          # 默认值有： arraybuffer | json | blob |text
          responseType?: 'json';# 这里，ts参数类型可选，默认值json，
          withCredentials?: boolean;
      }): Observable<Object>;

  • 故从源码我们可以知道，后端返回Hello,world,前端get方法会返回JSON解析异常。此时我们设置下responseType即可。

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    this.http.get(this.configUrl,{responseType:'text'})
    .subscribe((data: any) => this.config = { ...data });
解答问题二：
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this.http.get<Config>(
   this.configUrl, { observe: 'response' })
  .subscribe((data: any) => this.config = { ...data });
那么event 是干什么的呢？
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const request = new HttpRequest(
      "POST", this.uploadURL, {},{observe: 'events',reportProgress: true});
  this.http.request(request)
      .subscribe(
          event => {
              # 文件上传进度判定
              if (event.type === HttpEventType.DownloadProgress) {
                  console.log("Download progress event", event);
              }
              if (event.type === HttpEventType.UploadProgress) {
                  console.log("Upload progress event", event);
              }
              if (event.type === HttpEventType.Response) {
                  console.log("response received...", event.body);
              }

          }
      );

高级

GET请求

并行多个Get处理
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const parallel$ = Observable.forkJoin(
        this.http.get(url1),
        this.http.get(url2)
    );

parallel$.subscribe(
    values => {
        console.log("all values", values)
    }
);
串行多个Get请求
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const sequence$ = this.http.get<Config>(url1)
    .switchMap(config => {
        config.description+= ' - TEST ';
        return this.http.put(url2,config)
    });
sequence$.subscribe(
    values => console.log("result observable ", values) 
);
异常处理
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this.http
    .get("/api/simulate-error")
    .catch( error => {
        // here we can show an error message to the user,
        // for example via a service
        console.error("error catched", error);
        return Observable.of({description: "Error Value Emitted"});
    })
    .subscribe(
        val => console.log('Value emitted successfully', val),
        error => {
            console.error("This line is never called ",error);
        },
        () => console.log("HTTP Observable completed...")
    );
请求拦截
  • 定义鉴权拦截器
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    import {Injectable} from "@angular/core";
    import {HttpEvent, HttpHandler, HttpInterceptor} 
         from "@angular/common/http";
    import {HttpRequest} from "@angular/common/http";
    import {Observable} from "rxjs/Observable";

    @Injectable()
    export class AuthInterceptor implements HttpInterceptor {
        
        constructor(private authService: AuthService) {
        }

        intercept(req: HttpRequest<any>, 
                   next: HttpHandler):Observable<HttpEvent<any>> {
            
            const clonedRequest = req.clone({
                headers: req.headers.set(
                    'X-CustomAuthHeader', 
                    authService.getToken())
            });
            console.log("new headers", clonedRequest.headers.keys());
            return next.handle(clonedRequest);
        }
    }
  • 配置拦截器
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    @NgModule({
        declarations: [
            AppComponent
        ],
        imports: [
            BrowserModule,
            HttpClientModule
        ],
        providers: [
            [ 
               { 
                provide: HTTP_INTERCEPTORS, 
                useClass: AuthInterceptor,
                multi: true 
              }
            ]
        ],
        bootstrap: [AppComponent]
    })
    export class AppModule {
    }

参考

推荐

Angular8状态管理NgRx

前端Rollup+RxJs响应式编程实践

Angular8 httpclient简单入门

20个你值得了解的Angular开源项目

angular8 日常开发填坑指南

本文作者：前端analysis
联系邮箱：cheonghu@126.com
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Tags: angular http
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