如何使用composer autoloader自动加载我的类？

By considering this files structure

| -- src /
        | -- vendor
        | -- models
        | -- libraries
        | -- ...
        | -- composer.json

How can I autoload classes located in 'models' & 'libraries' directories ?

You can add your own autoloader rules into the composer.json file in your project - this adds your own rules to the vendor/autoload.php file so that your own classes will load as well as the ones in the vendor/ directory. There's more information in the docs here: https://getcomposer.org/doc/04-schema.md#autoload. Take a look at the PSR-0 section to load classes from your two directories.

Try something like:

{
    "autoload": {
        "psr-0": { "": ["models/", "libraries"] }
    }
}

If your classes are namespaced, then specify the namespaces as this will stop composer from looking for all classes in those directories.

Or later in code you can add your lib, example:

$loader = require(ROOTDIR . 'vendor/autoload.php'); // composer autoloading
//public function addPsr4($prefix, $paths, $prepend = false)
$loader->addPsr4('extend\\', ROOTDIR . 'class/lib'); 

$a = new \extend\MyClass(); // MyClass.php is in ROOTDIR/class/lib directory