java webApp asynchronous upload image implementation code

How to achieve java webApp asynchronously upload pictures, first understand the following questions:

1. Picture upload;
2. Picture upload preview;
3. Upload picture change address asynchronously add to database;

The main content
This example mainly USES the pure HTML front end and JavaScript code as tools. The code sample of demo's image upload implementation is as follows:
(1) click the div code of the uploaded image:

<div id="div1" class="photo"> 
 <input type="file" id="choose" accept="image/*" multiple >
 <a id="upload"> To upload pictures </a> 
 <a class="myinputimg" onclick="selectphoto();"> Select from the gallery </a>
 <a class="myinputimg" id="back"> cancel </a>
</div>

(2) javaScript code

<script type="text/javascript">
 // Get the uploaded image input The form elements 
 var filechooser = document.getElementById("choose");
 // Create for compressing the image canvas
 var canvas = document.createElement("canvas");
 // To obtain canvas Visual properties 
 var ctx = canvas.getContext('2d');
 // tiles canva
 var tCanvas = document.createElement("canvas");
 var tctx = tCanvas.getContext("2d");
 // Canvas size 
 var maxsize = 100 * 1024;
 // Upload image click event 
 $("#upload").on("click", function() {
  filechooser.click();
  })
  .on("touchstart", function() {
  // Add element attributes 
  $(this).addClass("touch");
  })
  .on("touchend", function() {
  // Remove element attributes 
  $(this).removeClass("touch");
  });
 // Element changes  
 filechooser.onchange = function() {
 // If the selection is null, return the operation 
 if (!this.files.length) return;
 // Create an array of uploaded images 
 var files = Array.prototype.slice.call(this.files);
 // Select the number greater than 1 Open, reverse operation, here according to the requirements set; pc The test 1 Can upload a number of pictures, mobile terminal selection 1 Zhang, the page can only be previewed 1 Zhang. Since it is a mobile terminal, make this judgment. 
 if (files.length >1) {
  alert("1 Secondary upload only 1 image ");
  return;
 }
 // Traverse the uploaded image file array, you don't need to traverse, directly access can. 
 files.forEach(function(file, i) {
 // Determine image format 
  if (!/\/(?:jpeg|png|gif)/i.test(file.type)) return;
  var reader = new FileReader();
  var li = document.createElement("li");
//    Get image size 
  var size = file.size / 1024 > 1024 ? (~~(10 * file.size / 1024 / 1024)) / 10 + "MB" : ~~(file.size / 1024) + "KB";
  // Preview picture 
  li.innerHTML = '<div class="progress"><span></span></div><div class="size">' + size + '</div>';
  // Add image preview code; 
  $(".img-list").append($(li));
  reader.onload = function() {
  var result = this.result;
  var img = new Image();
  img.src = result;
  // Picture shows 
  $(li).css("background-image", "url(" + result + ")");
  // If the image size is less than 100kb , then upload directly 
  if (result.length <= maxsize) {
   img = null;
   upload(result, file.type, $(li));
   return;
  }
//   After loading the image, compress it and upload it 
  if (img.complete) {
   callback();
  } else {
   img.onload = callback;
  }
  function callback() {
   var data = compress(img);
   upload(data, file.type, $(li));
   img = null;
  }
  };
  reader.readAsDataURL(file);
 });
 };
 // The following is the image compression related; 
 // use canvas Compress the large image 
 function compress(img) {
 var initSize = img.src.length;
 var width = img.width;
 var height = img.height;
 // If the picture is greater than 4 Megapixels, calculate the compression ratio and press the size to 400 All of the following 
 var ratio;
 if ((ratio = width * height / 4000000) > 1) {
  ratio = Math.sqrt(ratio);
  width /= ratio;
  height /= ratio;
 } else {
  ratio = 1;
 }
 canvas.width = width;
 canvas.height = height;
 // With the base 
 ctx.fillStyle = "#fff";
 ctx.fillRect(0, 0, canvas.width, canvas.height);
 // If the image is larger than pixels 100 Wan USES tiles 
 var count;
 if ((count = width * height / 1000000) > 1) {
  count = ~~(Math.sqrt(count) + 1); // Calculate how many tiles to divide into 
 //  Calculate the width and height of each tile 
  var nw = ~~(width / count);
  var nh = ~~(height / count);
  tCanvas.width = nw;
  tCanvas.height = nh;
  for (var i = 0; i < count; i++) {
  for (var j = 0; j < count; j++) {
   tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
   ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
  }
  }
 } else {
  ctx.drawImage(img, 0, 0, width, height);
 }
 // Minimum compression 
 var ndata = canvas.toDataURL('image/jpeg', 0.1);
 console.log(' Before compression: ' + initSize);
 console.log(' After the compression: ' + ndata.length);
 console.log(' The compression rate: ' + ~~(100 * (initSize - ndata.length) / initSize) + "%");
 tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
 return ndata;
 }
 // Picture upload, will base64 The picture turned into 2 Base object, insert formdata upload 
 function upload(basestr, type, $li) {
 var text = window.atob(basestr.split(",")[1]);
 var buffer = new Uint8Array(text.length);
 var pecent = 0, loop = null;
 for (var i = 0; i < text.length; i++) {
  buffer[i] = text.charCodeAt(i);
 }
 var blob = getBlob([buffer], type);
 var xhr = new XMLHttpRequest();
 var formdata = getFormData();
 formdata.append('upload', blob);
 // An asynchronous request kindeditor Upload image of plugin jsp page 
 xhr.open('post', '<%=request.getContextPath()%>/kindeditor/jsp/upload_json.jsp');
 xhr.onreadystatechange = function() {
  if (xhr.readyState == 4 && xhr.status == 200) { 
  // Returns the image address on the server side  
  var face_img=xhr.responseText;
  var id=$("#arId").text();
  // Asynchronously add a picture to the database 
  $.ajax({
   type:"POST",
   // An asynchronous request Struts the action Class inserts the image address into the database 
   url:"add_article_faceurl.action",
   dataType:"json",
   data:"faceurl="+face_img+"&id="+id,
   async:true,
   success: function(msg){ 
   // Gets the image associated with the add database id Value into the hidden area of the page 
    $("#arId").text(msg);
   },
   error: function(a){}
  });   
  }
 };
 // Simulated upload progress display 
 // Data delivery schedule, before 50% Show the progress 
 xhr.upload.addEventListener('progress', function(e) {
  if (loop) return;
  pecent = ~~(100 * e.loaded / e.total) / 2;
  $li.find(".progress span").css('width', pecent + "%");
  if (pecent == 50) {
  mockProgress();
  }
 }, false);
 // After the data 50% Simulate progress 
 function mockProgress() {
  if (loop) return;
  loop = setInterval(function() {
  pecent++;
  $li.find(".progress span").css('width', pecent + "%");
  if (pecent == 99) {
   clearInterval(loop);
  }
  }, 100);
 }
 xhr.send(formdata);
 }
 /**
 *  To obtain blob Object compatibility 
 * @param buffer
 * @param format
 * @returns {*}
 */
 function getBlob(buffer, format) {
 try {
  return new Blob(buffer, {type: format});
 } catch (e) {
  var bb = new (window.BlobBuilder || window.WebKitBlobBuilder || window.MSBlobBuilder);
  buffer.forEach(function(buf) {
  bb.append(buf);
  });
  return bb.getBlob(format);
 }
 }
 /**
 *  To obtain formdata
 */
 function getFormData() {
 var isNeedShim = ~navigator.userAgent.indexOf('Android')
  && ~navigator.vendor.indexOf('Google')
  && !~navigator.userAgent.indexOf('Chrome')
  && navigator.userAgent.match(/AppleWebKit\/(\d+)/).pop() <= 534;
 return isNeedShim ? new FormDataShim() : new FormData();
 }
 /**
 * formdata  The patch ,  For does not support formdata upload blob the android Machine patch 
 * @constructor
 */
 function FormDataShim() {
 console.warn('using formdata shim');
 var o = this,
  parts = [],
  boundary = Array(21).join('-') + (+new Date() * (1e16 * Math.random())).toString(36),
  oldSend = XMLHttpRequest.prototype.send;
 this.append = function(name, value, filename) {
  parts.push('--' + boundary + '\r\nContent-Disposition: form-data; name="' + name + '"');
  if (value instanceof Blob) {
  parts.push('; filename="' + (filename || 'blob') + '"\r\nContent-Type: ' + value.type + '\r\n\r\n');
  parts.push(value);
  }
  else {
  parts.push('\r\n\r\n' + value);
  }
  parts.push('\r\n');
 };
 // Override XHR send()
 XMLHttpRequest.prototype.send = function(val) {
  var fr,
   data,
   oXHR = this;
  if (val === o) {
  // Append the final boundary string
  parts.push('--' + boundary + '--\r\n');
  // Create the blob
  data = getBlob(parts);
  // Set up and read the blob into an array to be sent
  fr = new FileReader();
  fr.onload = function() {
   oldSend.call(oXHR, fr.result);
  };
  fr.onerror = function(err) {
   throw err;
  };
  fr.readAsArrayBuffer(data);
  // Set the multipart content type and boudary
  this.setRequestHeader('Content-Type', 'multipart/form-data; boundary=' + boundary);
  XMLHttpRequest.prototype.send = oldSend;
  }
  else {
  oldSend.call(this, val);
  }
 };
 }
</script>

(3) the code of jsp page of the uploaded picture of kindeditor plug-in.

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ page import="java.util.*,java.io.*" %>
<%@ page import="java.text.SimpleDateFormat" %>
<%@ page import="org.apache.commons.fileupload.*" %>
<%@ page import="org.apache.commons.fileupload.disk.*" %>
<%@ page import="org.apache.commons.fileupload.servlet.*" %>
<%@ page
 import="org.apache.struts2.dispatcher.multipart.MultiPartRequestWrapper"%>
<%@ page import="org.json.simple.*" %>
<%

/**
 * KindEditor JSP
 * 
 *  this JSP The program is a demonstration program and is not recommended to be used directly in real projects. 
 *  If you are sure to use this program directly, please carefully confirm the relevant security Settings before using it. 
 * 
 */

// The file saves the directory path 
String savePath = pageContext.getServletContext().getRealPath("/") + "attached/";
//String savePath = "http:\\\\192.168.1.226:8080\\qslnbase\\uploadFile/";
//String savePath = "D:/WWW/qslnADP/ADP/WebRoot/kindeditor/attached/";
// File save directory URL
String saveUrl = request.getContextPath() + "/attached/";
// Defines the file extensions that are allowed to be uploaded 
HashMap<String, String> extMap = new HashMap<String, String>();
extMap.put("image", "gif,jpg,jpeg,png,bmp,blob");
extMap.put("flash", "swf,flv");
extMap.put("media", "swf,flv,mp3,wav,wma,wmv,mid,avi,mpg,asf,rm,rmvb");
extMap.put("file", "doc,docx,xls,xlsx,ppt,htm,html,txt,zip,rar,gz,bz2");

// Maximum file size 
long maxSize = 1000000;

response.setContentType("text/html; charset=UTF-8");

if(!ServletFileUpload.isMultipartContent(request)){
 out.println(getError(" Please select the file. "));
 return;
}
// Check the directory 
File uploadDir = new File(savePath);
if(!uploadDir.isDirectory()){
 out.println(getError(" The upload directory does not exist. "));
 return;
}
// Check directory write permissions 
if(!uploadDir.canWrite()){
 out.println(getError(" Upload directory without write permission. "));
 return;
}

String dirName = request.getParameter("dir");
if (dirName == null) {
 dirName = "image";
}
if(!extMap.containsKey(dirName)){
 out.println(getError(" The directory name is incorrect. "));
 return;
}
// Create folders 
savePath += dirName + "/";
saveUrl += dirName + "/";
File saveDirFile = new File(savePath);
if (!saveDirFile.exists()) {
 saveDirFile.mkdirs();
}
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
String ymd = sdf.format(new Date());
savePath += ymd + "/";
saveUrl += ymd + "/";
File dirFile = new File(savePath);
if (!dirFile.exists()) {
 dirFile.mkdirs();
}
//Struts2  request   Packing filter 
MultiPartRequestWrapper wrapper = (MultiPartRequestWrapper) request;

// For the upload   The name of the file 
String fileName1 = wrapper.getFileNames("upload")[0];

// Get file filter 
File file = wrapper.getFiles("upload")[0];

// Check file size 
if(file.length() > maxSize){
 out.println(getError(" Upload file size over limit. "));
 return;
}

// Check the extension 
String fileExt1 = fileName1.substring(fileName1.lastIndexOf(".") + 1).toLowerCase();
// Refactor upload file name 
SimpleDateFormat df1 = new SimpleDateFormat("yyyyMMddHHmmss");
String newFileName1 = df1.format(new Date()) + "_" + new Random().nextInt(1000) + "." + fileExt1;

byte[] buffer = new byte[1024];
// Gets the file output stream 
FileOutputStream fos = new FileOutputStream(savePath + newFileName1);
String url=savePath + newFileName1;
out.println(url);
// Gets the current file input stream in memory 
InputStream in = new FileInputStream(file);

try {
 int num = 0;
 while ((num = in.read(buffer)) > 0) {
  fos.write(buffer, 0, num);
 }
} catch (Exception e) {
 e.printStackTrace(System.err);
} finally {
 in.close();
 fos.close();
}
%>
<%!
private String getError(String message) {
 JSONObject obj = new JSONObject();
 obj.put("error", 1);
 obj.put("message", message);
 return obj.toJSONString();
}
%>

(4) the jar package of pictures uploaded by kindeditor is shown below
A.commons-fileupload-1.2.1.jar
B.commons-io-1.4.jar
C.json_simple-1.1.jar

The js code about kindeditor is not used here, for details, please refer to: Kindeditor realizes the automatic image upload function

(5) div for kindeditor upload image preview is as follows

<div id="div2">
 <ul class="img-list">
  <li id="wy">
   <img style="height:100%;width:100%;position:absolute;top:0px;" src="<%=request.getContextPath()%>/shequ/images/index.png;" >
  </li>
 </ul> 
</div>