Angular HttpClient http请求示例（GET、PUT、 PATCH、POST、DEL

Getting Started With Angular 4.3+ HttpClient
将已有的项目添加到github
创建RESTAPI神器-JsonServer

1. Angular-cli新建httpClientExample项目
   ng new httpClientExample
2. ngModule中导入HttpClientModule
   typescript
....
import { HttpClientModule } from '@angular/common/http';
....
@NgModule({
declarations: [
AppComponent
],
imports: [
BrowserModule,
HttpClientModule
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule { }


3. npm安装json-server，代替api server提供API服务。(windows命令行提示符（管理员）)
   npm install -g json-server

   1. 新建一各 JSON 文件，扮演我们的服务器上的数据库。

      {
      "customers": [ { "id": 1,"name": "Customer001","email": "customer001@email.com","tel": "0526252525" },{ "id": 2,"name": "Customer002","email": "customer002@email.com","tel": "0527252525" },{ "id": 3,"name": "Customer003","email": "customer003@email.com","tel": "0528252525" } ] }

   2. 启动服务。现在可像用Rest service进行查询， json-server更多使用点击这里.
      json-server --watch E:db.json

4. HttpClient Get请求。

   1. 导入HttpClient ， @angular/common/http
   2. component 构造函数中注入HttpClient
   3. 使用.get（端点）方法创建HTTP GET请求

   4. 订阅(Subscribe )返回的observable并显示结果

      import { Component,OnInit } from '@angular/core';//OnInit 接口，要求实现OnInit方法。
      import { Observable } from "rxjs/Observable";//add
      import { HttpClient,} from "@angular/common/http";/add
      class Customer {
      id : number;
      name: string;
      email: string;
      tel: string;
      }    
      @Component({
      selector: 'customers',template: `
        <ul *ngIf="customersObservable | async as customers else empty">
            <li *ngFor="let customer of customers">
            {{customer|json}}
            </li> 
        </ul>
      `})   
      export class AppComponent implements OnInit {
      customersObservable : Observable<Customer[]>;    
      title = 'app';      
      constructor(private httpClient:HttpClient) {
      }
      ngOnInit() {//初始化时就开始get请求数据
      this.customersObservable = this.httpClient
          .get<Customer[]>("127.0.0.1:3000/customers");
      }
      }

5. HTTP GET 请求参数: HttpParams
   
   1. 请求第1页，最大条数2：
      
      1. url方式
         http://127.0.0.1:3000/customers?_page=1&_limit=1
      2. 使用httpClient实现
         
         1. 导入HttpParams
            import {HttpParams} from "@angular/common/http";
         2. 构建一个 HttpParams 对象
            const params = new HttpParams().set('_page',"1").set('_limit',"1");
         3. 呼叫 .get() 方法并携带参数，然后将返回的 Observable 对象分配给customersObservable。（params 要与get在同一个方法中）
            this.customersObservable = this.httpClient.get("http://127.0.0.1:3000/customers",{params});
         4. 使用更简单的方法新建HttpParams对象：【fromString】
            const params = new HttpParams({fromString: '_page=1&_limit=1'});
      3. 带参Get请求（记url QueryString）
         
const params = new HttpParams({fromString: '_page=1&_limit=1'});
this.customersObservable = this.http
.request("GET","http://127.0.0.1:3000/customers",
{
responseType:"json",
params
});

6. 添加 HTTP Headers
   
   1. 导入HttpHeaders
      import { HttpHeaders } from '@angular/common/http';
   2. 新建客制的HttpHeader对象
      const headers = new HttpHeaders().set("X-CustomHttpHeader","CUSTOM_VALUE");
   3. 发送带httpHeader的请求
      
const headers = new HttpHeaders().set("X-CustomHttpHeader","CUSTOM_VALUE");
this.customersObservable = this.httpClient.get("http://127.0.0.1:3000/customers",{headers});

   4. 携带httpHeader，会出现重复请求的状况，第一次Option请求 204状态（Firefox 为Option请求方法），第二次为返回的结果。
7. 发送HTTP PUT 请求
   HTTP PUT 方法用来完全替换 API server上的资源。用HttpClient 发送PUT 请求替换Customers上id为1的资源:
   
this.httpClient.put("http://127.0.0.1:3000/customers/1",
{
"name": "NewCustomer001",
"email": "newcustomer001@email.com",
"tel": "0000252525"
})
.subscribe(
data => {
console.log("PUT Request is successful ",data);
},
error => {
console.log("Rrror",error);
}
);

8. 发送HTTP PATCH 请求
   HTTP PATCH 用来更新API server上的资源。
   this.httpClient.patch("http://127.0.0.1:3000/customers/1",
{
"email": "newcustomer001@gmail.com"
})
.subscribe(
data => {
console.log("PUT Request is successful ",
error => {
console.log("Error",error);
}
);

9. 发送HTTP DELETE 请求
   HTTP DELETE 用来删除 API server上的资源
   this.httpClient.delete("http://127.0.0.1:3000/customers/1")
.subscribe(
data => {
console.log("DELETE Request is successful ",error);
}
);

10. 发送 HTTP POST 请求
    HTTP POST 方法有很多用途，大多数是用来在API server上新增一笔数据。
    this.httpClient.post("http://127.0.0.1:3000/customers",
{
"name": "Customer004",
"email": "customer004@email.com",
"tel": "0000252525"
})
.subscribe(
data => {
console.log("POST Request is successful ",error);
}
);


本地项目上传到GitHub

1. 先从github创建一个空的仓库
   先从github创建一个空的仓库，并复制链接地址
   
   复制repo链接
   
2. 初始化本地仓库，并提交内容到本地
   
   1. 如果没说明文档，如需，新建
      touch README.md
   2. 本地项目若未初始化，则初始化
      git init
   3. 添加全部已经修改的文件。
      git add . 等同git add -A
   4. 提交到本地
      git commit -m "提交说明"
3. 连接到远程仓库，并将代码同步到远程仓库
   
   1. git remote add origin 远程仓库地址。Git-基础
      git remote add origin https://github.com/Kiakaa/httpClientExample.git
   2. 推送到远程仓库
      git push -u origin master

完整代码链接

（编辑：李大同）

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