Next.js 15 Fullstack (App Router + Server Actions) · レッスン

Actionsによるファイルアップロード

安全な保存と処理を含め、Server Actionsを通じて直接ファイルアップロードを扱う方法を学びます

レッスン 2/311 ステップ

「Actionsによるファイルアップロード」はCoddyKit上の無料Next.js 15 Fullstack (App Router + Server Actions)レッスンです。これはレッスン2/3です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはNext.js 15 Fullstack (App Router + Server Actions)学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Next.js 15 Fullstack (App Router + Server Actions)コースには全3レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Uploading Files with Actions

File uploads are a common feature, allowing users to share images, documents, and more. Traditionally, handling these required complex API routes and separate handlers.

With Next.js Server Actions, handling file uploads becomes much simpler and more integrated directly within your forms, keeping your logic co-located.

Setting Up the File Input

To allow file uploads, you need an HTML form with a specific setup. The <input type="file"> element is essential for selecting files from a user's device.

Use the name attribute to identify the file in your Server Action.
Add enctype="multipart/form-data" to your <form> tag. This tells the browser to encode the form data, including files, correctly.

<form action="/api/upload" method="POST" enctype="multipart/form-data">
  <input type="file" name="myFile" />
  <button type="submit">Upload</button>
</form>

Capturing Files via FormData

When a form with enctype="multipart/form-data" is submitted to a Server Action, Next.js automatically parses the data into a FormData object.

You can access the uploaded file(s) from this FormData object using its get() method, which returns a standard JavaScript File object.

// app/actions.js
'use server';

export async function uploadFile(formData) {
  const file = formData.get('myFile');
  if (!file) {
    return { error: 'No file uploaded.' };
  }
  // 'file' is a File object
  console.log('File name:', file.name);
  console.log('File size:', file.size, 'bytes');
  console.log('File type:', file.type);
  return { success: true };
}

Exploring the File Object

The File object received in your Server Action is a powerful Web API object. It provides key information about the uploaded file:

name: The original filename provided by the user.
size: The file size in bytes.
type: The MIME type of the file (e.g., "image/jpeg", "application/pdf").
arrayBuffer(): An asynchronous method to get the file's content as an ArrayBuffer, which is crucial for saving it.

Storing Uploaded Files to Disk

To save the uploaded file permanently, you'll need to extract its content from the File object and write it to a storage location. The arrayBuffer() method helps convert the file into raw binary data.

You can then use Node.js's built-in fs/promises module to write this data to your server's file system.

// app/actions.js (continued)
'use server';
import { writeFile } from 'fs/promises';
import path from 'path';

export async function saveUploadedFile(formData) {
  const file = formData.get('myFile');
  if (!file || file.size === 0) return { error: 'No file.' };

  const buffer = Buffer.from(await file.arrayBuffer());
  const filename = Date.now() + '-' + file.name; // Unique filename
  const filePath = path.join(process.cwd(), 'public/uploads', filename);

  try {
    await writeFile(filePath, buffer);
    console.log('File saved to:', filePath);
    return { success: true, filename };
  } catch (error) {
    console.error('Error saving file:', error);
    return { error: 'Failed to save file.' };
  }
}

Validating File Uploads

It's crucial to validate uploaded files on the server-side to prevent security vulnerabilities and ensure data integrity. Always check:

File Type: Ensure the file's MIME type is among your allowed types (e.g., only images, not executable files).
File Size: Limit the maximum size to prevent denial-of-service attacks or excessive storage usage.

Client-side validation is helpful for user experience but can be bypassed, so server-side checks are mandatory.

Implementing Server-Side Validation

Here's how you can add basic type and size validation to your Server Action before saving the file. This makes your upload process much more robust and secure.

// app/actions.js (validation added)
'use server';
import { writeFile } from 'fs/promises';
import path from 'path';

const MAX_FILE_SIZE = 1024 * 1024 * 5; // 5MB
const ALLOWED_TYPES = ['image/jpeg', 'image/png', 'application/pdf'];

export async function validateAndSaveFile(formData) {
  const file = formData.get('myFile');
  if (!file || file.size === 0) return { error: 'No file.' };

  if (file.size > MAX_FILE_SIZE) {
    return { error: 'File too large (max 5MB).' };
  }
  if (!ALLOWED_TYPES.includes(file.type)) {
    return { error: 'Invalid file type.' };
  }

  const buffer = Buffer.from(await file.arrayBuffer());
  const filename = Date.now() + '-' + file.name;
  const filePath = path.join(process.cwd(), 'public/uploads', filename);

  await writeFile(filePath, buffer);
  return { success: true, filename };
}

Handling Multiple File Uploads

To allow users to upload multiple files at once, simply add the multiple attribute to your <input type="file"> tag.

On the server, formData.getAll('myFiles') will return an array of File objects, allowing you to iterate and process each one individually.

// HTML for multiple files:
<form action="/api/upload" method="POST" enctype="multipart/form-data">
  <input type="file" name="myFiles" multiple />
  <button type="submit">Upload</button>
</form>

// Server Action for multiple files:
'use server';

export async function uploadMultipleFiles(formData) {
  const files = formData.getAll('myFiles');
  if (!files || files.length === 0) return { error: 'No files.' };

  const uploadedNames = [];
  for (const file of files) {
    // Perform validation and saving for each file
    console.log('Processing file:', file.name);
    uploadedNames.push(file.name);
  }
  return { success: true, uploadedNames };
}

Beyond Local Storage

While saving files locally is suitable for development and small projects, production applications often use cloud storage solutions for scalability, reliability, and security.

Popular options include AWS S3, Google Cloud Storage, and Cloudinary. Server Actions can integrate directly with these services by sending the file's ArrayBuffer to their respective SDKs, providing robust storage capabilities.

File Upload Quiz

Which of the following HTML attributes is absolutely essential for a basic form to correctly send file data to a Next.js Server Action?

対話的なレッスンで答える

Recap & Next Steps

You've learned how to handle file uploads using Next.js Server Actions!

Set up HTML forms with enctype="multipart/form-data" and <input type="file">.
Access uploaded files as File objects from the FormData object in your Server Actions.
Save files to disk using Node.js fs/promises by converting the File object's content via Buffer.from(await file.arrayBuffer()).
Implement crucial server-side validation for file types and sizes to enhance security.
Handle multiple file uploads by adding the multiple attribute to the input and using formData.getAll().

Next, explore how to provide optimistic UI updates for a smoother user experience after an action!

無料で開始

AI チューターと学ぶ TypeScript — 無料

ブラウザでリアルコードを書いて実行し、24/7 の AI チューターから瞬時にサポートを受け、ウェブまたはアプリで続きから学習できます。

コース: 22
レッスン: 88

無料で学習を始めるコース全体を表示

よくある質問

「Actionsによるファイルアップロード」レッスンは無料ですか？

はい。「Actionsによるファイルアップロード」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Next.js 15 Fullstack (App Router + Server Actions)コースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Next.js 15 Fullstack (App Router + Server Actions)コースには全3レッスンが含まれています。

「Actionsによるファイルアップロード」で何を学びますか？

安全な保存と処理を含め、Server Actionsを通じて直接ファイルアップロードを扱う方法を学びますブラウザで直接実行するハンズオンコードでNext.js 15 Fullstack (App Router + Server Actions)を演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Next.js 15 Fullstack (App Router + Server Actions)を始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのNext.js 15 Fullstack (App Router + Server Actions)は初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/3です。

「Actionsによるファイルアップロード」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このNext.js 15 Fullstack (App Router + Server Actions)レッスンでコードを書いて実行できますか？

はい。すべてのNext.js 15 Fullstack (App Router + Server Actions)レッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

← Next.js 15 Fullstack (App Router + Server Actions)に戻る