Laravel的請求生命周期從public/index.php開始，經(jīng)過路由和中間件，再到控制器處理業(yè)務邏輯，最后通過異常處理返回響應。1. 所有請求首先由public/index.php捕獲并封裝為Request對象，啟動Laravel核心服務；2. 路由匹配后請求經(jīng)過中間件處理如認證、CSRF保護等，若中間件返回響應則終止后續(xù)流程；3. 請求到達控制器方法執(zhí)行業(yè)務邏輯，依賴自動注入，可能拋出異常；4. 異常由全局異常處理器捕獲，可自定義錯誤響應，最終生成響應返回瀏覽器。

當你're diving into Laravel, understanding how a request flows through the framework is key to building solid applications. It’s not just about knowing what each part does — it's about seeing how they work together from the moment a user hits your app until they get a response.

Here’s a breakdown of how the request lifecycle in Laravel typically goes, and what parts you should pay attention to as a developer.

1. The Entry Point: Public/index.php

Every HTTP request in Laravel starts at public/index.php. This is your application’s front controller. It loads the Composer autoloader and bootstraps the Laravel application using the kernel.

What happens here:

• The request is captured and wrapped in a Request object.
• Laravel fires up its core services (like configuration, routing, etc.).
• The kernel handles the request and prepares a response.

You don’t usually touch this file, but it's good to know it exists and that it’s where everything kicks off.

2. Routing and Middleware

Once the app is booted, Laravel checks the routes defined in routes/web.php or routes/api.php (depending on the request type). It matches the incoming URL and HTTP method (GET, POST, etc.) to a route.

Before hitting the actual route handler, the request goes through middleware. Middleware are layers that can modify the request or perform actions before and after handling it.

Common middleware tasks include:

• Authentication (auth)
• CSRF protection (VerifyCsrfToken)
• Logging requests
• CORS headers

If any middleware returns a response (e.g., redirecting an unauthenticated user), the rest of the route logic won't run.

3. Controllers and Business Logic

After passing through middleware, the request reaches the controller method or closure you defined in the route. This is where your main business logic lives — things like querying the database, processing forms, calling services, etc.

For example:

Route::get('/posts/{id}', [PostController::class, 'show']);

In this case, Laravel calls the show() method in PostController, passing along the {id} parameter from the URL.

Key points here:

• You can inject dependencies like Request objects or models directly into controller methods.
• Laravel uses service container to resolve these dependencies automatically.

This is also where exceptions might be thrown — like if a model isn't found — which leads us to the next step.

4. Exception Handling and Responses

Laravel has a global exception handler located in App/Exceptions/Handler.php. If something goes wrong during the request lifecycle — like a missing model or a validation error — Laravel catches the exception here.

You can customize how different exceptions are handled:

• Return specific HTTP responses (e.g., JSON for API errors)
• Log errors
• Redirect users

Finally, whatever response is generated — whether by a controller, middleware, or exception handler — gets sent back to the browser.

A Few Things to Keep in Mind

• Laravel caches some parts of the request lifecycle (like routes and config) for performance. Use php artisan config:clear or route:clear when debugging issues.
• Middleware order matters — especially for authentication and session handling.
• Exceptions in controllers or models can be caught globally, making it easier to maintain consistent error responses.

That’s basically how a request moves through Laravel. Once you understand this flow, debugging becomes easier, and structuring your code makes more sense.

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