Symfony2 - Composer messed up my site as all bundles don't exist - symfony

Question

Everything was great with my Symfony2 setup until I started messing around with Composer.
I did install Symfony2 with Composer, but then manually added bundles - including ones I created myself.
Then, I needed to add something which seemed easier with Composer. Lots of messing around in the Terminal later I then find when I run in a browser I get an error in AppKernel.php saying none of the bundles exist - including:
FatalErrorException: Error: Class 'Acme\DemoBundle\AcmeDemoBundle' not found in /path/app/AppKernel.php line 39
I'm 100% the folders exist and nothing has changed other than running various Composer commands.
Composer has no reference to these bundles.
How do I resolve this? I'm guessing I either tell Composer to clear off (like before) or somehow I get Composer to understand the bundles.
I'm guessing it has something to do with the bootstrap file. I believe Composer will create one after being updated, but this is where I'm struggling.
--
composer.json:
{
"name": "symfony/framework-standard-edition",
"description": "The \"Symfony Standard Edition\" distribution",
"autoload": {
"psr-0": { "": "src/" }
},
"require": {
"php": ">=5.3.3",
"symfony/symfony": "2.2.*",
"doctrine/orm": "~2.2,>=2.2.3",
"doctrine/doctrine-bundle": "1.2.*",
"twig/extensions": "1.0.*",
"symfony/assetic-bundle": "2.1.*",
"symfony/swiftmailer-bundle": "2.2.*",
"symfony/monolog-bundle": "2.2.*",
"sensio/distribution-bundle": "2.2.*",
"sensio/framework-extra-bundle": "2.2.*",
"sensio/generator-bundle": "2.2.*",
"jms/security-extra-bundle": "1.4.*",
"jms/di-extra-bundle": "1.3.*"
},
"scripts": {
"post-install-cmd": [
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
],
"post-update-cmd": [
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
]
},
"config": {
"bin-dir": "bin"
},
"minimum-stability": "alpha",
"extra": {
"symfony-web-dir": "web",
"symfony-app-dir": "app",
"branch-alias": {
"dev-master": "2.2-dev"
}
}
}

Answer 1

I think you didn't update app/autoload.php file. Check the source of standard distribution: https://github.com/symfony/symfony-standard/blob/master/app/autoload.php
You need to include vendor/autoload.php, which is generated by the composer.