src/app/services/version-info.service.ts

import { Injectable } from '@angular/core';
import { Http, Response, Headers } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/catch';
import 'rxjs/add/operator/map';
import 'rxjs/add/observable/throw';

import { SessionContext } from '../common/session-context';
import { BaseHttpService } from './base-http.service';
import { VersionInfo } from '../model/version-info';

import { MessageService } from './message.service';

@Injectable()
export class VersionInfoService extends BaseHttpService {

    constructor(
        private _http: Http,
        private _sessionContext: SessionContext,
        public messageService: MessageService
    ) {
        super(messageService);
    }

    public loadBackendServerInfo(): Observable<VersionInfo> {
        const headers = new Headers();
        this.createCommonHeaders(headers, this._sessionContext);
        return this._http.get(super.getBaseUrl() + '/versionInfo', { headers: headers })
            .map(resp => super.extractData(resp, this._sessionContext))
            .catch(error => {
                return super.handleErrorPromise(error);
            });
    }
}