https://majing.io/posts/10000020421171

import { NgModule }         from '@angular/core';
import { BrowserModule }    from '@angular/platform-browser';
import { HttpClientModule } from '@angular/common/http';
@NgModule({
  imports: [
    BrowserModule,
    HttpClientModule,
  ],
  declarations: [
    AppComponent,
  ],
  bootstrap: [ AppComponent ]
})
export class AppModule {}

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
@Injectable()
export class ConfigService {
  constructor(private http: HttpClient) { }
  getData() {
    return this.http.get(this.dataUrl);
  }
}

http.get(url).subscribe(...)

http.get(url).map(res => res.json()).subscribe(...)

getTextFile(filename: string) {
  return this.http.get(filename, {responseType: 'text'})
    .pipe(
      tap( 
        data => this.log(filename, data),
        error => this.logError(filename, error)
      )
    );
}

之前 激动人心的 Angular HttpClient 这篇文章已经介绍过 HttpClient ，今天看到 angular-university 博客中介绍 HttpClient 的文章，内容很详细，我就简单做了整理。有兴趣的话，建议直接阅读 原文。

HttpClientModule 应用

导入新的 HTTP Module

import {HttpClientModule} from '@angular/common/http';
@NgModule({
declarations: [
AppComponent
],
imports: [
BrowserModule,
HttpClientModule
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule {}

需要注意的是，现在 JSON 是默认的数据格式，我们不需要再进行显式的解析。即我们不需要再使用以下代码：

http.get(url).map(res => res.json()).subscribe(...)

现在我们可以这样写：

http.get(url).subscribe(...)

发送 Get 请求

import {Component, OnInit} from '@angular/core';
import {Observable} from "rxjs/Observable";
import {HttpClient} from "@angular/common/http";
import * as _ from 'lodash';
interface Course {
description: string;
courseListIcon:string;
iconUrl:string;
longDescription:string;
url:string;
}
@Component({
  selector: 'app-root',
  template: `
      <ul *ngIf="courses$ | async as courses else noData">
          <li *ngFor="let course of courses">
              {{course.description}}
          </li> 
      </ul>
      <ng-template #noData>No Data Available</ng-template>
  `})
export class AppComponent implements OnInit {
courses$: Observable<any>;
constructor(private http:HttpClient) {}
ngOnInit() {
this.courses$ = this.http
.get("https://angular-http-guide.firebaseio.com/courses.json")
.map(data => _.values(data))
.do(console.log);
}
}

设置查询参数

假设发送 Get 请求时，需要设置对应的查询参数，预期的 URL 地址如下：

https://angular-http-guide.firebaseio.com/courses.json?orderBy="$key"&limitToFirst=1

创建 HttpParams 对象

import {HttpParams} from "@angular/common/http";
const params = new HttpParams()
.set('orderBy', '"$key"')
.set('limitToFirst', "1");
this.courses$ = this.http
.get("/courses.json", {params})
.do(console.log)
.map(data => _.values(data))

需要注意的是，我们通过链式语法调用 set() 方法，构建 HttpParams 对象。这是因为 HttpParams 对象是不可变的，通过 set()方法可以防止该对象被修改。

每当调用 set() 方法，将会返回包含新值的 HttpParams 对象，因此如果使用下面的方式，将不能正确的设置参数。

const params = new HttpParams();
params.set('orderBy', '"$key"')
params.set('limitToFirst', "1");

使用 fromString 语法

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

使用 request() API

const params = new HttpParams({fromString: 'orderBy="$key"&limitToFirst=1'});
this.courses$ = this.http
.request(
"GET",
"/courses.json",
{
responseType:"json",
params
})
.do(console.log)
.map(data => _.values(data));

设置 HTTP Headers

const headers = new HttpHeaders().set("X-CustomHeader", "custom header value");
this.courses$ = this.http
.get(
"/courses.json",
{headers})
.do(console.log)
.map(data => _.values(data));

发送 Put 请求

httpPutExample() {
const headers = new HttpHeaders().set("Content-Type", "application/json");
this.http.put("/courses/-KgVwECOnlc-LHb_B0cQ.json",
{
"courseListIcon": ".../main-page-logo-small-hat.png",
"description": "Angular Tutorial For Beginners TEST",
"iconUrl": ".../angular2-for-beginners.jpg",
"longDescription": "...",
"url": "new-value-for-url"
},
{headers})
.subscribe(
val => {
console.log("PUT call successful value returned in body",
val);
},
response => {
console.log("PUT call in error", response);
},
() => {
console.log("The PUT observable is now completed.");
}
);
}

发送 Patch 请求

httpPatchExample() {
this.http.patch("/courses/-KgVwECOnlc-LHb_B0cQ.json",
{
"description": "Angular Tutorial For Beginners PATCH TEST",
})
.subscribe(
(val) => {
console.log("PATCH call successful value returned in body",
val);
},
response => {
console.log("PATCH call in error", response);
},
() => {
console.log("The PATCH observable is now completed.");
});
}

发送 Delete 请求

httpDeleteExample() {
this.http.delete("/courses/-KgVwECOnlc-LHb_B0cQ.json")
.subscribe(
(val) => {
console.log("DELETE call successful value returned in body",
val);
},
response => {
console.log("DELETE call in error", response);
},
() => {
console.log("The DELETE observable is now completed.");
});
}

发送 Post 请求

httpPostExample() {
this.http.post("/courses/-KgVwECOnlc-LHb_B0cQ.json",
{
"courseListIcon": "...",
"description": "TEST",
"iconUrl": "..",
"longDescription": "...",
"url": "new-url"
})
.subscribe(
(val) => {
console.log("POST call successful value returned in body",
val);
},
response => {
console.log("POST call in error", response);
},
() => {
console.log("The POST observable is now completed.");
});
}

避免重复请求

duplicateRequestsExample() {
const httpGet$ = this.http
.get("/courses.json")
.map(data => _.values(data));
httpGet$.subscribe(
(val) => console.log("logging GET value", val)
);
this.courses$ = httpGet$;
}

在上面例子中，我们正在创建了一个 HTTP observable 对象 httpGet$，接着我们直接订阅该对象。然后，我们把 httpGet$ 对象赋值给 courses$ 成员变量，最后在模板中使用 async 管道订阅该对象。

这将导致发送两个 HTTP 请求，在这种情况下，请求显然是重复的，因为我们只希望从后端查询一次数据。为了避免发送冗余的请求，我们可以使用 RxJS 提供的 shareReplay 操作符：

// put this next to the other RxJs operator imports
import 'rxjs/add/operator/shareReplay';
const httpGet$ = this.http
.get("/courses.json")
.map(data => _.values(data))
.shareReplay();

并行发送多个请求

并行发送 HTTP 请求的一种方法是使用 RxJs 中的 forkjoin 操作符：

import 'rxjs/add/observable/forkJoin';
parallelRequests() {
const parallel$ = Observable.forkJoin(
this.http.get('/courses/-KgVwEBq5wbFnjj7O8Fp.json'),
this.http.get('/courses/-KgVwECOnlc-LHb_B0cQ.json')
);
parallel$.subscribe(
values => {
console.log("all values", values)
}
);
}

顺序发送 Http 请求

sequentialRequests() {
const sequence$ = this.http.get<Course>('/courses/-KgVwEBq5wbFnjj7O8Fp.json')
.switchMap(course => {
course.description+= ' - TEST ';
return this.http.put('/courses/-KgVwEBq5wbFnjj7O8Fp.json', course)
});
sequence$.subscribe();
}

获取顺序发送 Http 请求的结果

sequentialRequests() {
const sequence$ = this.http.get<Course>('/courses/-KgVwEBq5wbFnjj7O8Fp.json')
.switchMap(course => {
course.description+= ' - TEST ';
return this.http.put('/courses/-KgVwEBq5wbFnjj7O8Fp.json', course)
},
(firstHTTPResult, secondHTTPResult)  => [firstHTTPResult, secondHTTPResult]);
sequence$.subscribe(values => console.log("result observable ", values) );
}

请求异常处理

throwError() {
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...")
);
}

当发生异常时，控制台的输出结果：

Error catched 
HttpErrorResponse {headers: HttpHeaders, status: 404, statusText: "Not Found", url: "http://localhost:4200/api/simulate-error", ok: false, … }
Value emitted successfully {description: "Error Value Emitted"}
HTTP Observable completed...

Http 拦截器

定义拦截器

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

@NgModule({
declarations: [
AppComponent
],
imports: [
BrowserModule,
HttpClientModule
],
providers: [
[ { provide: HTTP_INTERCEPTORS, useClass: AuthInterceptor, multi: true } ]
],
bootstrap: [AppComponent]
})
export class AppModule { }

Http 进度事件

longRequest() {
const request = new HttpRequest(
"POST", "/api/test-request", {},
{reportProgress: true});
this.http.request(request)
.subscribe(
event => {
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);
}
}
);
}

上面示例运行后，控制台的可能的输出结果：

Upload progress event Object {type: 1, loaded: 2, total: 2}
Download progress event Object {type: 3, loaded: 31, total: 31}
Response Received... Object {description: "POST Response"}