Bdtjtk

From Java standpoint using Exceptions to handle EXPECTED outcomes is wrong (Exceptions should be what they are called).

For all my services I've created wrapper mechanism that basically gives details on failure if such happens (all returns are arbitrary Result<?>). Now I need to display this message on client browser in some popup.

With Angular there is HttpClient that actually supports catching http response errors:
https://angular.io/guide/http#error-handling

Is this a viable way of reporting error from server to client?

Is there a way in Angular to define some extractor that would split responses from backend API?

Say I'd make my whole REST API return bodies:

{

    messageType: "", // Success, Failure, Warning

    message: "Message",

    content: {

        ...

    }

}

And that way I could strip message, messageType in interceptor, display them in popup, and pass only content further as body?

A good way to capture all exceptions at service side using @ControllerAdvice and throw the user/feature specific exceptions with the expected exception message and status code in standard structure so that front end can have an exception controller to evaluate this exception message on a fly in popup message dynamic to any message from service.

Since I came to web from pure Java backends - Exceptions in JAVA are bad (generally speaking), why follow same bad practices (using errors as info) when using HTTP?
After some more reading I can say - don't unless its actually an error, e.g:

• 404 if client tries to access entity with ID that is not there.


• 500 when server ACTUALLY can't handle something (actual Exception).

Here is Angular part for my Result<?> system.

Interceptor:

import { Injectable } from '@angular/core';

import { HttpEvent, HttpInterceptor, HttpHandler, HttpRequest, HttpResponse } from '@angular/common/http';



import { Observable } from 'rxjs';

import { map } from 'rxjs/operators';



import { Globals } from '../globals.service';



@Injectable()

export class PopupInterceptor implements HttpInterceptor {



    constructor(private globals: Globals) { }



    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

        if (req.url.startsWith(this.globals.apiHost)) {

            return next.handle(req)

                .pipe(

                    map(e => {

                        if (e instanceof HttpResponse) {

                            const response = <Response>e.body;

                            // use response to do whatever - I am injecting popup service and pushing response.message there for display in component.

                            return e.clone({ body: response.result });

                        }

                    })

                );

        }

        return next.handle(req);

    }

}



interface Response {

    type: string;

    message: string;

    result: any;

}

globals.service:

import { Injectable } from '@angular/core';



@Injectable({

    providedIn: 'root'

})

export class Globals {

    apiHost = '/api/';

}

app.module:

providers: [

        { provide: HTTP_INTERCEPTORS, useClass: PopupInterceptor, multi: true }

    ],