How to disable caching with HttpClient get in Angu

问题:

I'm writing an Angular SPA app, that uses HttpClient to get values from my backend.

What is the easy way to tell it not to cache? The first time I ask it gets the value, then it refuses to make subsequent queries.

Thanks, Gerry

回答1:

Using meta HTML tags, Disable browser caching:-

<meta http-equiv="cache-control" content="no-cache, must-revalidate, post-check=0, pre-check=0">
<meta http-equiv="expires" content="0">
<meta http-equiv="pragma" content="no-cache">

or,

Add headers in http request as:-

headers = new Headers({
        'Cache-Control':  'no-cache, no-store, must-revalidate, post- 
                            check=0, pre-check=0',
        'Pragma': 'no-cache',
        'Expires': '0'
    });

回答2:

HTTPInterceptors are great way to modify HTTP requests occurring in your application. It acts as an injectable service that can invoke when HttpRequest occurs.

HTTP Interceptor:

import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpHeaders } from '@angular/common/http';

@Injectable()
export class CacheInterceptor implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler) {
    const httpRequest = req.clone({
      headers: new HttpHeaders({
        'Cache-Control': 'no-cache',
        'Pragma': 'no-cache',
        'Expires': 'Sat, 01 Jan 2000 00:00:00 GMT'
      })
    });

    return next.handle(httpRequest);
  }
}

Using Interceptor:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';

import { AppComponent } from './app.component';

import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';
import { CacheInterceptor } from './http-interceptors/cache-interceptor';

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

回答3:

As answered by Pramod, you can use http request interceptor to modify or set a new header on the request. Below is a much simpler way of setting headers on http request interceptor for Later angular versions(Angular 4+). This approach would only set or update a certain request header. This is to avoid removing or overriding some important headers like the authorization header.

// cache-interceptor.service.ts
import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
} from '@angular/common/http';

@Injectable()
export class CacheInterceptor implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler) {
    const httpRequest = req.clone({
      headers: req.headers
        .set('Cache-Control', 'no-cache')
        .set('Pragma', 'no-cache')
        .set('Expires', 'Sat, 01 Jan 2000 00:00:00 GMT')
    })

    return next.handle(httpRequest)
  }
}

// app.module.ts

  import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http'
  import { CacheInterceptor } from './cache-interceptor.service';

  // on providers
  providers: [{ provide: HTTP_INTERCEPTORS, useClass: CacheInterceptor, multi: true }]