How to add a custom exception on symfony2

Question

I am new to Symfony(using version 2.2) and trying to add a custom exception listener. I have read the following links but cannot get it to work.

• Overriding Sym

Answer 1

I just had to add \ and the global scope worked in a Symfony service

namespace App\CoreBundle\Service;

class CurrencyExchange
{
    const RATES_XML = 'https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml?849b4b329863b2d60bfd0de486e423c9';

    const RATES_XML_PATH = 'uploads/ecb_currencies.xml';

    /** @var array $rates */
    private $rates;

    public function __construct()
    {
        if (!is_file(self::RATES_XML_PATH)) {
            throw new \Exception('XML '.self::RATES_XML_PATH.' does not exists.');
        }

        if (1 > filesize(self::RATES_XML_PATH)) {
            throw new \Exception('XML '.self::RATES_XML_PATH.' is empty.');
        }