How to use Laravel to implement file upload and download functions
Laravel is a popular PHP web framework that provides a wealth of functions and tools to make developing web applications easier and more efficient . One of the commonly used functions is file upload and download. This article will introduce how to use Laravel to implement file upload and download functions, and provide specific code examples.

1. File upload
   File upload refers to uploading local files to the server for storage. In Laravel, we can use the file upload class to handle the logic of file upload. The following are the steps to implement file upload:

Step 1: Create a file upload form
First, we need to create a file upload form on the front end. You can use the HTML

<input type="file" name="file">
<button type="submit">上傳</button>

Step 2: Process the file upload logic
Then, process the file upload logic in Laravel's controller. First, we need to introduce the file upload class:

use IlluminateHttpRequest;

Then, obtain the uploaded file through the Request object and save it to the server. The example is as follows:

public function upload(Request $request)
{

if ($request->hasFile('file')) {
    $file = $request->file('file');
    $filename = $file->getClientOriginalName();
    $file->move(public_path('uploads'), $filename);
}

}

In the above code, we first pass $request->hasFile() Method to determine whether a file has been uploaded. If a file is uploaded, we obtain the file object through the $request->file() method. Then, we can get the original file name through the getClientOriginalName() method and save the file to the specified directory on the server through the move() method.

2. File download
   File download refers to downloading files from the server and saving them locally. In Laravel, we can implement file downloading functions through routing and controllers. The following are the steps to implement file download:

Step 1: Create a download route
First, we need to create a download route in the routes/web.php file. An example is as follows:

Route::get('/download/{filename}', 'DownloadController@download');

In the above code, we define a route /download/{filename }, where {filename} represents the name of the file to be downloaded. The route will call the download() method in the DownloadController controller.

Step 2: Create a Download Controller
Then, we need to create a DownloadController controller. You can create a controller in the command line through the following command:

php artisan make:controller DownloadController

Then, implement the download() method in the DownloadController controller, the specific code is as follows:

public function download($filename)
{

$file = public_path('uploads/' . $filename);
return response()->download($file);

}

In the above code, we first obtain the absolute path of the file through the public_path() method. Then, the file is returned to the client for download through the response()->download() method.

3. Complete code example
   The above are the steps to implement simple file upload and download functions. The following is a complete sample code:

// Route
Route::get('/download/{filename}', 'DownloadController@download');
Route:: post('/upload', 'UploadController@upload');

// UploadController.php

namespace AppHttpControllers;

use IlluminateHttpRequest;

class UploadController extends Controller
{

public function upload(Request $request)
{
    if ($request->hasFile('file')) {
        $file = $request->file('file');
        $filename = $file->getClientOriginalName();
        $file->move(public_path('uploads'), $filename);
    }
    
    return redirect('/');
}

}

// DownloadController.php

namespace AppHttpControllers;

class DownloadController extends Controller
{

public function download($filename)
{
    $file = public_path('uploads/' . $filename);
    return response()->download($file);
}

}

In the above code, we created two controllers, UploadController and DownloadController, to handle file uploads and downloads. logic. Then, we defined two routes /upload and /download/{filename}, which correspond to the file upload and download functions respectively. Through the above steps, we can implement the file upload and download functions in Laravel.

Summary
Through the above steps, we can use Laravel to implement file upload and download functions. For file upload, we need to create a file upload form on the front end and process the file upload logic on the back end; for file download, we need to define the download logic through routing and controllers, and return the file to the client for downloading . Through these steps, we can easily implement file upload and download functions in Laravel.

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