Nodejs advanced: file upload based on express+multer

Environment initialization

is very simple, just one line of command.

npm install express multer multer --save

Below each example, there are the following two files

➜ upload-custom-filename git:(master) ✗ tree -L 1.
├── app.js # Server-side code, used to process file upload requests├── form.html # Front-end page, used to upload files

Basic example: single image upload

Please refer to here for the complete sample code.

app.js.

var fs = require('fs');
var express = require('express');
var multer  = require('multer')

var app = express();
var upload = multer({ dest: 'upload/' });

// 单图上传
app.post('/upload', upload.single('logo'), function(req, res, next){
    res.send({ret_code: '0'});
});

app.get('/form', function(req, res, next){
    var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
    res.send(form);
});

app.listen(3000);

form.html.

<form action="/upload-single" method="post" enctype="multipart/form-data">
    <h2 id="单图上传">单图上传</h2>
    <input type="file" name="logo">
    <input type="submit" value="提交">
</form>

Run the service.

node app.js

Visit http://127.0.0.1:3000/form, select the picture, click "Submit", done. Then, you will see an additional image in the upload directory.

Basic example: multi-image upload

Please refer to here for the complete sample code.

The code couldn't be simpler, just change the previous upload.single('logo') to upload.array('logo', 2). Indicates: Supports uploading 2 images at the same time, and the name attribute is logo.

app.js.

var fs = require('fs');
var express = require('express');
var multer  = require('multer')

var app = express();
var upload = multer({ dest: 'upload/' });

// 多图上传
app.post('/upload', upload.array('logo', 2), function(req, res, next){
    res.send({ret_code: '0'});
});

app.get('/form', function(req, res, next){
    var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
    res.send(form);
});

app.listen(3000);

form.html.

<form action="/upload-multi" method="post" enctype="multipart/form-data">
    <h2 id="多图上传">多图上传</h2>
    <input type="file" name="logos">
    <input type="file" name="logos">
    <input type="submit" value="提交">
</form>

The same test steps, no need to repeat them.

Get information about uploaded images

Please refer to here for the complete sample code.

Many times, in addition to saving images on the server, we also need to do many other things, such as storing image information in the database.

Commonly used information such as original file name, file type, file size, local save path, etc. With the help of multer, we can easily obtain this information.

This is still an example of single file upload. At this time, multer will write the file information to req.file, as shown in the following code.

app.js.

var fs = require('fs');
var express = require('express');
var multer  = require('multer')

var app = express();
var upload = multer({ dest: 'upload/' });

// 单图上传
app.post('/upload', upload.single('logo'), function(req, res, next){
    var file = req.file;

    console.log('文件类型：%s', file.mimetype);
    console.log('原始文件名：%s', file.originalname);
    console.log('文件大小：%s', file.size);
    console.log('文件保存路径：%s', file.path);

    res.send({ret_code: '0'});
});

app.get('/form', function(req, res, next){
    var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
    res.send(form);
});

app.listen(3000);

form.html.

<form action="/upload" method="post" enctype="multipart/form-data">
    <h2 id="单图上传">单图上传</h2>
    <input type="file" name="logo">
    <input type="submit" value="提交">
</form>

Start the service and upload the file, you will see the information printed on the console.

File type: image/png
Original file name: 1.png
File size: 18379 File saving path: upload/b7e4bb22375695d92689e45b551873d9

Customized file upload path, name

Sometimes, we want to customize file upload The path, name, and multer can also be easily implemented.

Customizing the local saving path

is very simple. For example, if we want to upload files to the my-upload directory, just modify the dest configuration item.

var upload = multer({ dest: 'upload/' });

Under the above configuration, all resources are saved in the same directory. Sometimes we need to personalize settings for different files, then you can refer to the next section.

Customize the locally saved file name

Please refer to here for the complete sample code.

The code is a little longer, but just as simple. Multer provides the storage parameter to personalize the path and file name of resource saving.

Usage notes are as follows:

destination: Set the saving path of the resource. Note that without this configuration item, it will be saved under /tmp/uploads by default. Additionally, the path needs to be created yourself.

filename: Set the file name of the resource saved locally.

app.js.

var fs = require('fs');
var express = require('express');
var multer  = require('multer')

var app = express();

var createFolder = function(folder){
    try{
        fs.accessSync(folder); 
    }catch(e){
        fs.mkdirSync(folder);
    }  
};

var uploadFolder = './upload/';

createFolder(uploadFolder);

// 通过 filename 属性定制
var storage = multer.diskStorage({
    destination: function (req, file, cb) {
        cb(null, uploadFolder);    // 保存的路径，备注：需要自己创建
    },
    filename: function (req, file, cb) {
        // 将保存文件名设置为 字段名 + 时间戳，比如 logo-1478521468943
        cb(null, file.fieldname + '-' + Date.now());  
    }
});

// 通过 storage 选项来对 上传行为 进行定制化
var upload = multer({ storage: storage })

// 单图上传
app.post('/upload', upload.single('logo'), function(req, res, next){
    var file = req.file;
    res.send({ret_code: '0'});
});

app.get('/form', function(req, res, next){
    var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
    res.send(form);
});

app.listen(3000);

form.html.

<form action="/upload" method="post" enctype="multipart/form-data">
    <h2 id="单图上传">单图上传</h2>
    <input type="file" name="logo">
    <input type="submit" value="提交">
</form>

I won’t go into details about the test steps, just visit it and you will know the effect.

Written at the back

This article introduces the basic usage of multer and does not cover too many principles. As the saying goes, it is better to teach a man to fish than to teach him to fish. In the following chapters, the details of file uploading will be excavated so that readers can have a deeper understanding of file uploading.