laravel中的设计模式.md

探索laravel中的设计模式

前言：laravel作为一个纯面向对象框架，使用了很多优秀的设计模式

一、工厂模式

拥有某些共性的功能可以使用工厂模式进行封装，使得维护者维护便利，使用者使用便利

栗子1：redis的连接，使用简单工厂

interface Factory
{
    // 通过名字获取连接
    public function connection($name = null);
}

class RedisManager implements Factory
{
    // 通过名字获取连接
    public function connection($name = null)
    {
        $name = $name ?: 'default';

        if (isset($this->connections[$name])) {
            return $this->connections[$name];
        }

        return $this->connections[$name] = $this->configure(
            $this->resolve($name), $name
        );
    }
    // 解析名字获得连接
    public function resolve($name = null)
    {
        $name = $name ?: 'default';

        $options = $this->config['options'] ?? [];

        if (isset($this->config[$name])) {
            return $this->connector()->connect($this->config[$name], $options);
        }

        throw new InvalidArgumentException("Redis connection [{$name}] not configured.");
    }
    // 通过驱动选择连接，这里提供了predis和phpredis选择
    protected function connector()
    {
        switch ($this->driver) {
            case 'predis':
                return new Connectors\PredisConnector;
            case 'phpredis':
                return new Connectors\PhpRedisConnector;
        }
    }
}

栗子2：数据库的连接，同样使用简单工厂

interface ConnectionResolverInterface
{
    public function connection($name = null);
}

class DatabaseManager implements ConnectionResolverInterface
{
    public function connection($name = null)
    {
        [$database, $type] = $this->parseConnectionName($name);

        $name = $name ?: $database;

        // If we haven't created this connection, we'll create it based on the config
        // provided in the application. Once we've created the connections we will
        // set the "fetch mode" for PDO which determines the query return types.
        if (! isset($this->connections[$name])) {
            $this->connections[$name] = $this->configure(
                $this->makeConnection($database), $type
            );
        }

        return $this->connections[$name];
    }
    
    protected function makeConnection($name)
    {
        $config = $this->configuration($name);

        // First we will check by the connection name to see if an extension has been
        // registered specifically for that connection. If it has we will call the
        // Closure and pass it the config allowing it to resolve the connection.
        if (isset($this->extensions[$name])) {
            return call_user_func($this->extensions[$name], $config, $name);
        }

        // Next we will check to see if an extension has been registered for a driver
        // and will call the Closure if so, which allows us to have a more generic
        // resolver for the drivers themselves which applies to all connections.
        if (isset($this->extensions[$driver = $config['driver']])) {
            return call_user_func($this->extensions[$driver], $config, $name);
        }

        return $this->factory->make($config, $name);
    }
}

class ConnectionFactory
{
    public function make(array $config, $name = null)
    {
        $config = $this->parseConfig($config, $name);

        if (isset($config['read'])) {
            return $this->createReadWriteConnection($config);
        }

        return $this->createSingleConnection($config);
    }
    
    public function createConnector(array $config)
    {
        if (! isset($config['driver'])) {
            throw new InvalidArgumentException('A driver must be specified.');
        }

        if ($this->container->bound($key = "db.connector.{$config['driver']}")) {
            return $this->container->make($key);
        }

        switch ($config['driver']) {
            case 'mysql':
                return new MySqlConnector;
            case 'pgsql':
                return new PostgresConnector;
            case 'sqlite':
                return new SQLiteConnector;
            case 'sqlsrv':
                return new SqlServerConnector;
        }

        throw new InvalidArgumentException("Unsupported driver [{$config['driver']}]");
    }
}

二、单例模式

保证类只实例化一次，减少不必要的开销

栗子：容器的实例化

class Container implements ArrayAccess, ContainerContract
{
    protected static $instance;

	public static function getInstance()
    {
        if (is_null(static::$instance)) {
            static::$instance = new static;
        }

        return static::$instance;
    }
}

三、观察者模式

类似于发布订阅

namespace Illuminate\Contracts\Events;
interface Dispatcher
{
    public function listen($events, $listener);
    public function dispatch($event, $payload = [], $halt = false);
}

use Illuminate\Contracts\Events\Dispatcher as DispatcherContract;
class Dispatcher implements DispatcherContract
{
    // 监听
    public function listen($events, $listener)
    {
        foreach ((array) $events as $event) {
            if (Str::contains($event, '*')) {
                $this->setupWildcardListen($event, $listener);
            } else {
                $this->listeners[$event][] = $this->makeListener($listener);
            }
        }
    }
    // 发布
    public function dispatch($event, $payload = [], $halt = false)
    {
        // When the given "event" is actually an object we will assume it is an event
        // object and use the class as the event name and this event itself as the
        // payload to the handler, which makes object based events quite simple.
        [$event, $payload] = $this->parseEventAndPayload(
            $event, $payload
        );

        if ($this->shouldBroadcast($payload)) {
            $this->broadcastEvent($payload[0]);
        }

        $responses = [];

        foreach ($this->getListeners($event) as $listener) {
            $response = $listener($event, $payload);

            // If a response is returned from the listener and event halting is enabled
            // we will just return this response, and not call the rest of the event
            // listeners. Otherwise we will add the response on the response list.
            if ($halt && ! is_null($response)) {
                return $response;
            }

            // If a boolean false is returned from a listener, we will stop propagating
            // the event to any further listeners down in the chain, else we keep on
            // looping through the listeners and firing every one in our sequence.
            if ($response === false) {
                break;
            }

            $responses[] = $response;
        }

        return $halt ? null : $responses;
    }
}