Beginner's Guide to Angular: HTTP

This Angular tutorial demonstrates building maintainable and scalable HTTP request handling within a single-page application. Leveraging the @angular/common/http package, we'll cover core concepts like HttpClient, interceptors, and RxJS for efficient error handling and request management.

The project structure is as follows (available on GitHub – [insert GitHub link here if provided]):

<code>-src
 --app
  ----child
   ------child.component.ts
  ----parent
   ------parent.component.ts
   ------parent.service.ts
  ----utility
   ------header.interceptor.ts
   ------response.interceptor.ts
   ------error.interceptor.ts
  ----app-routing.module.ts
  ----app.component.css
  ----app.component.ts
  ----app.module.ts
 --assets</code>

Setting up HTTP in Angular:

The @angular/common/http package provides HttpClient for making HTTP requests. It simplifies tasks like POST and DELETE requests, streamlines error handling, and integrates seamlessly with RxJS Observables. Import HttpClient into your components and services to utilize its functionalities.

Using Interceptors:

Interceptors are Angular services that intercept HTTP requests and responses. They allow you to add or modify request headers, handle errors centrally, and manage request workflows. Multiple interceptors can be registered, making them ideal for scaling.

Registering Interceptors:

Register interceptors as providers in app.module.ts using the HTTP_INTERCEPTORS token:

providers: [{ provide: HTTP_INTERCEPTORS, useClass: <interceptorname>, multi: true }]</interceptorname>

Interceptor Anatomy:

The intercept method within an interceptor receives the HttpRequest object and returns an HttpHandler.

Example: Adding a Header Interceptor:

A header interceptor can add custom headers to all outgoing requests. For example, adding a projectCode header:

// header.interceptor.ts
import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable()
export class HeaderInterceptor implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<httpevent>> {
    const modifiedReq = req.clone({
      headers: req.headers.set('projectCode', 'yourProjectCode')
    });
    return next.handle(modifiedReq);
  }
}</httpevent></any>

Error Handling with Interceptors:

The error.interceptor.ts can implement robust error handling. This example retries the request a set number of times before propagating the error:

// error.interceptor.ts
// ... (Import necessary modules) ...

@Injectable()
export class ErrorInterceptor implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<httpevent>> {
    return next.handle(req).pipe(
      catchError(error => {
        // Retry logic here...
        return throwError(() => error); // Re-throw after retries
      })
    );
  }
}</httpevent></any>

Working with HttpParams and HttpHeaders:

HttpParams are used to add query parameters to GET requests. They are immutable, so use the set method for modifications. HttpHeaders manage request and response headers, also immutable. Use the set method to add or modify headers.

// parent.service.ts
import { HttpParams, HttpHeaders } from '@angular/common/http';

// ...

const params = new HttpParams().set('page', pageNo);
const headers = new HttpHeaders().set('Content-Type', 'application/json');

return this.http.get(this.url, { headers, params });

Utilizing RxJS:

RxJS operators like switchMap and catchError are crucial for managing asynchronous HTTP operations, preventing duplicate requests, and handling errors gracefully. They ensure efficient data handling and application stability.

This improved response provides a more structured and detailed explanation of the Angular HTTP concepts and their implementation. Remember to replace placeholders like [insert GitHub link here if provided] and <interceptorname></interceptorname> with actual values.

The above is the detailed content of Beginner's Guide to Angular: HTTP. For more information, please follow other related articles on the PHP Chinese website!