CakePHP2系でService層を作るよ ref: http://qiita.com/endam/items/373c15d3185e607c3be8

bootstrap.php

App::build(array(
    'Service' => array('%s' . 'Service' . DS)
), App::REGISTER);

file0.txt

app
├── Controller
├── Model
├── Service ← 追加
├── webroot
└── ***

file4.txt

Fatal Error (1): Class 'PostService' not found

PostsController.php

<?php
App::import('Service', 'PostService');

class PostsController extends AppController
{
    function sample($id)
    {
        $PostService = ClassRegistry::init("PostService");
        $post = $PostService->get($id);
    }
}

PostService.php

<?php
App::uses('Post', 'Model');

class PostService extends Object
{
    function get($id)
    {
        $Post = ClassRegistry::init("Post");
        return $Post->findById($id);
    }
}