Angular 4 http CORS No 'Access-Control-Allow-Origin' with a java servlet

If you still want to use CORS while developing you can solve this kind of issue using angular/cli --proxy-config.

Essentially, if you want to make requests to a remote machine having, for example, nginx web server running, you perform all your calls to your very same application, e.g. localhost:4200 (default in angular/cli). Then you redirect those responses to your server using --proxy-config.

Let's suppose your server's api have all the /api prefix entrypoint. You need to create a file called proxy.config.json in the root of your project and configure it like:

{
    "/api" : {
        "target" : "http://xx.xxx.xxx.xx", // Your remote address
        "secure" : false,
        "logLevel" : "debug", // Making Debug Logs in console
        "changeOrigin": true
    }
}

And then, all your http requests will point to localhost:4200/api/.

Finally, you should be done by running ng server --proxy-config proxy.config.json.

If you notice that some headers are missing in the request, add them from your web server or edit your http.service.ts to append those like in this example:

import { Injectable } from '@angular/core';
import { Http, Headers, RequestOptions } from '@angular/http';
import { Observable } from 'rxjs/Rx';
import { isNull } from 'lodash';

@Injectable()
export class HttpClientService {

  private _host: string;
  private _authToken: string;
  private _options: RequestOptions = null;

  constructor(private _http: Http, private _config: AppConfig, private _localStorageService: LocalStorageService) {
      this._host = ''; // Your Host here, get it from a configuration file
      this._authToken = ''; // Your token here, get it from API
  }

  /**
   * @returns {RequestOptions}
   */
   createAuthorizationHeader(): RequestOptions {
      // Just checking is this._options is null using lodash
      if (isNull(this._options)) {
        const headers = new Headers();
        headers.append('Content-Type', 'application/json; charset=utf-8');
        headers.append('Authorization', this._authToken);
        this._options = new RequestOptions({headers: headers});
      }
      return this._options;
   }

   /**
    * @param url {string}
    * @param data {Object}
    * @return {Observable<any>}
    */
    get(url?: string, data?: Object): Observable<any> {
      const options = this.createAuthorizationHeader();
      return this._http.get(this._host + url, options);
    }

   /**
    * @param url {string}
    * @param data {Object}
    * @return {Observable<any>}
    */
    post(url?: string, data?: Object): Observable<any> {
      const body = JSON.stringify(data);
      const options = this.createAuthorizationHeader();
      return this._http.post(this._host + url, body, options);
    }

}

So, you would perform all of your api calls through this service like

import { Component, OnInit } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { HttpClientService } from './http.service.ts';

export class TestComponent implements OnInit {

  _observable: Observable<any> = null;

  constructor(private _http: HttpClientService) { }

  ngOnInit() {
      this._observable = this _http.get('test/')
                .map((response: Response) => console.log(response.json()));
  }

}

Angular 5 Update:

In app.module.ts now you need to replace import { HttpModule } from '@angular/http'; with import { HttpClientModule } from '@angular/common/http';.

The service changes a bit to:

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { isNull, isUndefined } from 'lodash';

@Injectable()
export class HttpClientService {

  private _host: string;
  private _authToken: string;
  private __headers: HttpHeaders;

  constructor(private _http: HttpClient, private _config: AppConfig, private _localStorageService: LocalStorageService) {
      this._host = ''; // Your Host here, get it from a configuration file
      this._authToken = ''; // Your token here, get it from API
  }

  /**
   * @returns {HttpHeaders}
   */
   createAuthorizationHeader(): HttpHeaders {
      // Just checking is this._options is null using lodash
      if (isNull(this.__headers)) {
        const headers = new HttpHeaders()
           .set('Content-Type', 'application/json; charset=utf-8')
           .set('Authorization', this. _authToken || '');
        this.__headers= new RequestOptions({headers: headers});
      }

      return this.__headers;
   }

   /**
    * @param url {string}
    * @param data {Object}
    * @return {Observable<any>}
    */
    get(url?: string, data?: Object): Observable<any> {
      const options = this.createAuthorizationHeader();
      return this._http.get(this._host + url, {
          headers : this.createAuthorizationHeader()
      });
    }

   /**
    * @param url {string}
    * @param data {Object}
    * @return {Observable<any>}
    */
    post(url?: string, data?: Object): Observable<any> {
      const body = JSON.stringify(data);
      const options = this.createAuthorizationHeader();
      return this._http.post(this._host + url, body, {
          headers : this.createAuthorizationHeader()
      });
    }
}

You may use Angular CLI proxy tooling for this purpose.

• 1. you create a file proxy.config.json at the root of your project
• 2. you map your API URLs to target URLs using this syntax

 "/api/xxxxxxx" : {
        "target" : "http://www.api.com/xxxxxxx", 
        "secure" : false,
        "logLevel" : "debug",
        "changeOrigin": true
    }

• 3. Serve your application using

ng serve --proxy-config proxy.config.json