为了减少UserController中的逻辑代码，可以把大部分的操作放到Service中来处理，这样使得控制器中的代码变得更简洁。

1. 在Service目录下创建UserService类，具体代码如下：

<?php
/**
 * Created by PhpStorm.
 * User: mac
 * Date: 2018/11/27
 * Time: 下午2:02
 */

namespace App\Service;


use App\Entity\User;
use App\Repository\UserRepository;
use Symfony\Component\HttpFoundation\Request;

class UserService
{
    /**
     * @var UserRepository
     */
    private $userRepository;

    public function __construct(UserRepository $userRepository)
    {
        $this->userRepository = $userRepository;
    }

    /**
     * @param int $userId
     * @return User|null 返回一个User实例或Null
     */
    public function getUser(int $userId): ?User
    {
        return $this->userRepository->find($userId);
    }

    /**
     * 获取所有用户
     *
     * @return array|null
     */
    public function getUsers(): ?array
    {
        return $this->userRepository->findAll();
    }

    /**
     * 添加用户
     *
     * @param Request $request
     * @return User
     */
    public function addUser(Request $request): User
    {
        $user = new User();
        $name = $request->get('name');
        $user->setName($name);
        $pass = $request->get('pass');
        $encrypt_pass = password_hash(trim($pass), PASSWORD_BCRYPT);
        $user->setPass($encrypt_pass);
        if ($mail = $request->get('mail')) {
            $user->setMail($mail);
        } else {
            $user->setMail($name . '@xxx.cn');
        }

        return $user;
    }

    /**
     * 更新用户
     *
     * @param int $userId
     * @param Request $request
     * @return User|null
     */
    public function updateUser(int $userId, Request $request) : ?User
    {
        $user = $this->userRepository->find($userId);
        if (!$user) {
            return null;
        }
        if ($mail = $request->get('mail')) {
            $user->setMail($mail);
        }

        return $user;
    }

}

2. 修改UserController部分代码

#添加构造函数，把UserService实例放到$userService属性中
 public function __construct(UserService $userService)
    {
        $this->userService = $userService;
    }

    /**
     * 注册-生成用户
     *
     * @Rest\Post("/users")
     * @param Request $request
     * @return View
     */
    public function post(Request $request): View
    {
        $user = $this->userService->addUser($request);
        $em = $this->getDoctrine()->getManager();
        $em->persist($user);
        $em->flush();

        return View::create($user, Response::HTTP_CREATED);
    }

    /**
     * 获取用户信息
     *
     * @Rest\Get("/users/{userId}")
     * @return View
     */
    public function getAction(int $userId) :View
    {
        $user = $this->userService->getUser($userId);
        return View::create($user, Response::HTTP_OK);
    }

    /**
     * 获取所有用户信息
     *
     * @Rest\Get("/users")
     * @return View
     */
    public function list() :View
    {
        $users = $this->userService->getUsers();
        return View::create($users, Response::HTTP_OK);
    }