[JAVA] Image upload function with Vue.js + Flask

Overview

This time, we will create an image recognition application that uses Vue.js for the front end and Flask for the back end. For the time being, this time we will implement the image upload function.

environment

• Docker
• Vue-cli
• flask (pipenv)

The environment was built in the above environment. See the links below for instructions and details.

Vue + Flask on Docker

Explanation of key points

Vue The following code explains the details.

Home.vue

//Upload image to server
    onUploadImage () {
      var params = new FormData()
      params.append('image', this.uploadedImage)
      //I am posting the data converted to FormData using Axios to Flask.
      axios.post(`${API_URL}/classification`, params).then(function (response) {
        console.log(response)
    })

1. The acquired image is Base64-converted. "Data: image / jpeg: base64, ~"
2. With FormData, data is converted to "key: value" format by HTTP request.
3. Apply Axios and send data with '127 .0.0.1: 5000 / classification' + POST method.

Flask

The following code explains the details.

app.py

@app.route('/classification', methods=['POST'])
def uploadImage():
    if request.method == 'POST':
        base64_png =  request.form['image']
        code = base64.b64decode(base64_png.split(',')[1]) 
        image_decoded = Image.open(BytesIO(code))
        image_decoded.save(Path(app.config['UPLOAD_FOLDER']) / 'image.png')
        return make_response(jsonify({'result': 'success'}))
    else: 
        return make_response(jsonify({'result': 'invalid method'}), 400)

1. "data: image / jpeg: base64, ~" exists inside FormData. Get the file name.
2. Get an image with Pillow (PIL).
3. Save the image.

Overall picture

Vue

Home.vue

<template>
  <div>
    <div class="imgContent">
      <div class="imagePreview">
        <img :src="uploadedImage" style="width:100%;" />
      </div>
      <input type="file" class="file_input" name="photo" @change="onFileChange"  accept="image/*" />
      <button @click='onUploadImage'>Please judge the image ...</button>
    </div>
  </div>
</template>

<script>
import axios from 'axios'

const API_URL = 'http://127.0.0.1:5000'
export default {
  data () {
    return {
      uploadedImage: ''
    }
  },
  methods: {
    //Reflect the selected image
    onFileChange (e) {
      let files = e.target.files || e.dataTransfer.files
      this.createImage(files[0])
    },
    //View uploaded image
    createImage (file) {
      let reader = new FileReader()
      reader.onload = (e) => {
        this.uploadedImage = e.target.result
      }
      reader.readAsDataURL(file)
    },
    //Upload image to server
    onUploadImage () {
      var params = new FormData()
      params.append('image', this.uploadedImage)
      //I am posting the data converted to FormData using Axios to Flask.
      axios.post(`${API_URL}/classification`, params).then(function (response) {
        console.log(response)
      })
    }
  }
}
</script>

Flask

Points to remember

--CORS allows resources to be shared by different origins (protocols, domains, ports). --CORS is required if you have different web applications. --Japanese is supported by app.config ['JSON_AS_ASCII'] = False.

app.py

# render_template: Specify the template to refer to
#jsonify: json output
from flask import Flask, render_template, jsonify, request, make_response

#CORS: Library for Ajax communication
from flask_restful import Api, Resource
from flask_cors import CORS 
from random import *
from PIL import Image
from pathlib import Path
from io import BytesIO
import base64

# static_folder: Specify the path of the static file built with vue
# template_folder: index built with vue.Specify html path
app = Flask(__name__, static_folder = "./../frontend/dist/static", template_folder="./../frontend/dist")

#Japanese
app.config['JSON_AS_ASCII'] = False
#CORS=Terms for secure communication with Ajax
api = Api(app)
CORS(app)

UPLOAD_FOLDER = './uploads'
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER

#Index when receiving any request.See html
@app.route('/', defaults={'path': ''})
@app.route('/<path:path>')
def index(path):
    return render_template("index.html")

@app.route('/classification', methods=['POST'])
def uploadImage():
    if request.method == 'POST':
        base64_png =  request.form['image']
        code = base64.b64decode(base64_png.split(',')[1]) 
        image_decoded = Image.open(BytesIO(code))
        image_decoded.save(Path(app.config['UPLOAD_FOLDER']) / 'image.png')
        return make_response(jsonify({'result': 'success'}))
    else: 
        return make_response(jsonify({'result': 'invalid method'}), 400)

# app.run(host, port): Start flask server by specifying host and port
if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

State

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https://developer.mozilla.org/ja/docs/Web/HTTP/CORS POST image, face detection, draw on face with canvas