摘要：我們?cè)谶@個(gè)類中的方法看到如下代碼，一個(gè)典型的過濾器，在這個(gè)中獲取的方法是。，整個(gè)初始化的過程總結(jié)下巧妙的使用了面向?qū)ο蟮慕涌诜绞剑瑸槲覀兲峁┝烁鞣N各樣不同的存儲(chǔ)方式，一旦我們了解了存儲(chǔ)方式和加密規(guī)則，讓不同的容器進(jìn)行共享的目的也可以達(dá)到

前些天，為了解答一個(gè)問題，就去研究了Laravel的源碼，講講我的收獲：
這個(gè)是問題源：
http://segmentfault.com/q/1010000003776645?_ea=365137

本文講的Laravel全部使用5.1版本。

我們首先看Laravel是如何創(chuàng)建Session組件的。
首先我們可以看見在Kernel.php中注冊(cè)了StartSession這個(gè)類（這里不去討論Laravel的DI和IoC），看下這個(gè)類是如何使用的。

我們?cè)谶@個(gè)類中的handle方法看到如下代碼

public function handle($request, Closure $next)
{
    $this->sessionHandled = true;

    // If a session driver has been configured, we will need to start the session here
    // so that the data is ready for an application. Note that the Laravel sessions
    // do not make use of PHP "native" sessions in any way since they are crappy.
    if ($this->sessionConfigured()) {
        $session = $this->startSession($request);

        $request->setSession($session);
    }

    $response = $next($request);

    // Again, if the session has been configured we will need to close out the session
    // so that the attributes may be persisted to some storage medium. We will also
    // add the session identifier cookie to the application response headers now.
    if ($this->sessionConfigured()) {
        $this->storeCurrentUrl($request, $session);

        $this->collectGarbage($session);

        $this->addCookieToResponse($response, $session);
    }

    return $response;
}

OK，一個(gè)典型的過濾器，在這個(gè)StartSession中獲取Session的方法是getSession。

它使用了Laravel注入的SessionManager 這個(gè)類的完整限定名是：IlluminateSessionSessionManager

/**
 * Start the session for the given request.
 *
 * @param  IlluminateHttpRequest  $request
 * @return IlluminateSessionSessionInterface
 */
protected function startSession(Request $request)
{
    with($session = $this->getSession($request))->setRequestOnHandler($request);

    $session->start();

    return $session;
}

/**
 * Get the session implementation from the manager.
 *
 * @param  IlluminateHttpRequest  $request
 * @return IlluminateSessionSessionInterface
 */
public function getSession(Request $request)
{
    $session = $this->manager->driver();
    $session->setId($request->cookies->get($session->getName()));

    return $session;
}

我們?cè)谶@個(gè)函數(shù)中看到，它調(diào)用了SessionManager的drive方法，drive方法是SessionManager的父類Manager中定義的，看到它的實(shí)現(xiàn)是這樣的

/**
 * Get a driver instance.
 *
 * @param  string  $driver
 * @return mixed
 */
public function driver($driver = null)
{
    $driver = $driver ?: $this->getDefaultDriver();

    // If the given driver has not been created before, we will create the instances
    // here and cache it so we can return it next time very quickly. If there is
    // already a driver created by this name, we"ll just return that instance.
    if (! isset($this->drivers[$driver])) {
        $this->drivers[$driver] = $this->createDriver($driver);
    }

    return $this->drivers[$driver];
}

/**
 * Create a new driver instance.
 *
 * @param  string  $driver
 * @return mixed
 *
 * @throws InvalidArgumentException
 */
protected function createDriver($driver)
{
    $method = "create".ucfirst($driver)."Driver";

    // We"ll check to see if a creator method exists for the given driver. If not we
    // will check for a custom driver creator, which allows developers to create
    // drivers using their own customized driver creator Closure to create it.
    if (isset($this->customCreators[$driver])) {
        return $this->callCustomCreator($driver);
    } elseif (method_exists($this, $method)) {
        return $this->$method();
    }

    throw new InvalidArgumentException("Driver [$driver] not supported.");
}

也就是調(diào)用getDefaultDriver方法

/**
 * Get the default session driver name.
 *
 * @return string
 */
public function getDefaultDriver()
{
    return $this->app["config"]["session.driver"];
}

這里就是我們?cè)?b>app/config/session.php中定義的driver字段，獲取這個(gè)字段后，我們可以從createDriver的源碼看到，它實(shí)際上是調(diào)用createXXXXDriver的方式獲取到driver的。

OK，我們看下最簡單的File，也就是createFileDriver

/**
 * Create an instance of the file session driver.
 *
 * @return IlluminateSessionStore
 */
protected function createFileDriver()
{
    return $this->createNativeDriver();
}

/**
 * Create an instance of the file session driver.
 *
 * @return IlluminateSessionStore
 */
protected function createNativeDriver()
{
    $path = $this->app["config"]["session.files"];

    return $this->buildSession(new FileSessionHandler($this->app["files"], $path));
}

/**
 * Build the session instance.
 *
 * @param  SessionHandlerInterface  $handler
 * @return IlluminateSessionStore
 */
protected function buildSession($handler)
{
    if ($this->app["config"]["session.encrypt"]) {
        return new EncryptedStore(
            $this->app["config"]["session.cookie"], $handler, $this->app["encrypter"]
        );
    } else {
        return new Store($this->app["config"]["session.cookie"], $handler);
    }
}

這個(gè)Store就是我們Session的實(shí)體了，它的具體讀寫調(diào)用使用抽象的Handler進(jìn)行，也就是說如果是讀文件，就new FileHandler如果是Redis就是new RedisHandler實(shí)現(xiàn)read和write即可。

回到StartSession 這個(gè)類，我們?cè)倏?b>getSession這個(gè)方法

 $session->setId($request->cookies->get($session->getName()));

了解Web的人都應(yīng)該知道，session是根據(jù)cookie中存的key來區(qū)分不同的會(huì)話的，所以sessionId尤為重要，這里我們先不關(guān)心Cookie是如何讀取，我們知道在這里讀取了cookie中存放的SessionId就夠了。

接下去看怎么加載數(shù)據(jù)

依然是StartSession這個(gè)類，
我們看startSession這個(gè)方法，下一句調(diào)用的就是$session->start();，這句話是干嘛呢？經(jīng)過前面的分析，我們知道$session已經(jīng)是Store對(duì)象了，那么它的start方法如下：

public function start()
{
    $this->loadSession();

    if (! $this->has("_token")) {
        $this->regenerateToken();
    }

    return $this->started = true;
}

/**
 * Load the session data from the handler.
 *
 * @return void
 */
protected function loadSession()
{
    $this->attributes = array_merge($this->attributes, $this->readFromHandler());

    foreach (array_merge($this->bags, [$this->metaBag]) as $bag) {
        $this->initializeLocalBag($bag);

        $bag->initialize($this->bagData[$bag->getStorageKey()]);
    }
}

 /**
 * Read the session data from the handler.
 *
 * @return array
 */
protected function readFromHandler()
{
    $data = $this->handler->read($this->getId());

    if ($data) {
        $data = @unserialize($this->prepareForUnserialize($data));

        if ($data !== false && $data !== null && is_array($data)) {
            return $data;
        }
    }

    return [];
}

依次調(diào)用了loadSession和readFromHandler 好，可以看到從handler中調(diào)用了read方法，這個(gè)方法就是從我們之前定義的各種handler中讀取數(shù)據(jù)了，它是個(gè)抽象方法，在子類中具體實(shí)現(xiàn)，然后返回給Store（存入到Store中的attributes數(shù)組中去了，到此為止，Session的初始化方法都結(jié)束了，

public function get($name, $default = null)
{
    return Arr::get($this->attributes, $name, $default);
}

這個(gè)函數(shù)去讀取Session中的數(shù)據(jù)了。

OK，Session整個(gè)初始化的過程總結(jié)下：

StartSession#handle -> StartSession#startSession -> StartSession#getSession -> SessionManager#getDefaultDriver -> SessionManager#createXXXHandler -> Store -> Store#setId -> Store#startSession

Laravel巧妙的使用了面向?qū)ο蟮?b>接口方式，為我們提供了各種各樣不同的存儲(chǔ)方式，一旦我們了解了存儲(chǔ)方式和加密規(guī)則，讓不同的web容器進(jìn)行Session共享的目的也可以達(dá)到~