Run the php artisan make:middleware command to quickly create middleware, used to process logic before or after request, such as permission verification, logging, etc.; 1. The functions of middleware include authentication, permission control, logging, and adding response headers; 2. After using the command to generate middleware, edit the handle method to implement pre-or-post logic; 3. Register middleware must be bound in the $routeMiddleware array of Kernel.php, and then called through the middleware method in the route; 4. Note that the middleware execution order is an onion model, avoid output content and dead loops, and the $next parameter cannot be omitted.

When you run php artisan make:middleware command, Laravel will help you quickly create a middleware class. This middleware can be used to process logic before or after request, such as permission verification, logging, etc.

Here are a few key points and steps you need to know:

The role and applicable scenarios of middleware

Middleware plays an important role in the Laravel request lifecycle. It is located before the request enters the route or after the response returns to the browser, and is often used in the following situations:

• User authentication (such as login or not)
• Permission control (such as whether it is an administrator)
• Log access logs
• Add response header information

You can understand it as a "door guard" and do some inspections or pre-processing before release.

How to generate middleware using commands

Run the following Artisan command to create a middleware:

 php artisan make:middleware CheckAdmin

This generates a file named CheckAdmin.php in app/Http/Middleware/ directory. You can edit the logic in it.

The default generated middleware structure is as follows:

 public function handle(Request $request, Closure $next)
{
    // Write your pre-logical $response = $next($request);

    // Write your post-logical return $response here;
}

• $request is the current HTTP request object.
• $next is the closure that calls the next middleware or final controller.
• $response is the response returned from the subsequent process.

How to register and use middleware

Generating middleware is only the first step, and it also needs to be registered to take effect.

The steps are as follows:

1. Bind middleware to kernel
   Open app/Http/Kernel.php file and add a line to the $routeMiddleware array:

    'admin' => \App\Http\Middleware\CheckAdmin::class,

2. Using middleware in routing

   Add ->middleware('admin') when defining the route:

    Route::get('/dashboard', function () {
       return view('dashboard');
   })->middleware('admin');

3. Multiple middleware can also be used together

    ->middleware(['auth', 'admin'])

   ---

   Some FAQs and Notes

   • Middleware execution order : If you have multiple middleware, they will execute the pre-logic in order of registration, and then reverse the post-logic (similar to the onion model).
   • Don't output content in middleware : unless you have special needs, it is recommended to only make logical judgments and not directly output HTML or JSON.
   • Avoid dead loops : For example, jumping to the same route in middleware can easily lead to infinite redirection.
   • The Closure parameter must be retained : even if you do not use it, $next parameter cannot be omitted, otherwise the request process will be interrupted.

   ---

   Basically that's it. Creating middleware is not complicated by itself, but the combination and logical design between middleware will affect the structure and security of the entire project, so it should be planned and used reasonably.

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