How do I read from parameters.yml in a controller in symfony2?

In Symfony 2.6 and older versions, to get a parameter in a controller – you should get the container first, and then – the needed parameter.

$this->container->getParameter('api_user');

This documentation chapter explains it.

While $this->get() method in a controller will load a service (doc)

In Symfony 2.7 and newer versions, to get a parameter in a controller you can use the following:

$this->getParameter('api_user');