防止Observable在服务器关闭时重试

有一个重试方法可以自动重新订阅一个失败的可观察到的指定次数。重新订阅httpclient方法调用的结果具有重新发出HTTP请求的效果。

this.http.get<User[]>(SERVER_API_URL + '/api/not_found')
        .pipe(
          retry(0), // retry a failed request up to 0 times
          catchError(this.handleError) // then handle the error
        ).subscribe(...);
    }

https://angular.io/guide/http

    const sub = this.http.get<User[]>(SERVER_API_URL + '/api/not_found')
        .subscribe(
            value => {
                console.log('subscribe.next')
                sub.unsubscribe();
            },
            err => {
                console.log('subscribe.error');
                sub.unsubscribe();
            },
            () => console.log('subscribe.done')
        );