通过XMLHttpRequest的progress来实现监听图片上传的进度，实时显示百分比，后台保存图片成功后再将图片转为Base64编码的字符串在前端显示出来，这样可以很大程度提高用户体验
需要达到的效果：
1、用户可以看到图片上传进度条百分比
2、提升图片回显速度(将图片转为Base64编码的字符串在前端显示)
HTML代码:
JS代码：
// 上传input绑定一个change事件
$("#uploadImage").on("change", uploadPicture());
// 上传方法，里面处理进度条逻辑
function uploadPicture() {
var $this= $(this);
document.getElementById("showProgress").style.display="block";
var fd = new FormData();
fd.append("file", $this.context.files[0]);
var xhr = new XMLHttpRequest();
//上传中设置上传的百分比
xhr.upload.addEventListener("progress", function(evt){
if (evt.lengthComputable) {
var percentComplete = Math.round(evt.loaded * 100 / evt.total);
if (percentComplete == 100){
setTimeout(function () {
document.getElementById("showProgress").innerHTML = '已上传'+percentComplete+"%";
},1500)
}else{
document.getElementById("showProgress").innerHTML = '已上传'+percentComplete+"%";
}
}else {
document.getElementById("showProgress").innerHTML = '无法计算';
}
}, false);
//请求完成后执行的操作
亨达代理申请https://www.kaifx.cn/broker/hantecmarkets.html
xhr.addEventListener("load", function(evt){
var message = evt.target.responseText,
obj = eval("("+message+")");
$("#uploadImage").attr("src",obj);
document.getElementById("showProgress").style.display="none";
alert("上传成功!");
}, false);
//请求error
xhr.addEventListener("error", uploadFailed, false);
//请求中断
xhr.addEventListener("abort", uploadCanceled, false);
//发送请求
xhr.open("POST", /uploadPicture.json);
xhr.send(fd);
}
function uploadFailed(evt) {
alert("上传出错.");
}
function uploadCanceled(evt) {
alert("上传已由用户或浏览器取消删除连接.");
}
后台代码：
/**
* 上传图片
* @param request
* @return
*/
@RequestMapping(value = "/uploadPicture", method = RequestMethod.POST)
@ResponseBody
public String uploadPicture(HttpServletRequest request) {
MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
Iterator iter = multipartRequest.getFileNames();
MultipartFile file = null;
while (iter.hasNext()) {
file = multipartRequest.getFile(iter.next());
}
CommonsMultipartFile cFile = (CommonsMultipartFile) file;
DiskFileItem fileItem = (DiskFileItem) cFile.getFileItem();
String filePath = "";
byte[] data = null;
String originalFilename = file.getOriginalFilename();
try {
String fileType = originalFilename.substring(
originalFilename.lastIndexOf(".") + 1).toLowerCase();
float bb = bytes2kb(file.getSize());
if (bb > 10) {
throw new Exception("文件上传失败，最大上传大小为10M。");
}
filePath = 上传图片方法，这里改为自己公司的;
// 转为输入流
InputStream inputStream = fileItem.getInputStream();
data = new byte[inputStream.available()];
inputStream.read(data);
inputStream.close();
// 对字节数组进行Base64编码，得到Base64编码的字符串
BASE64Encoder encoder = new BASE64Encoder();
String base64Str = encoder.encode(data);
return "data:image/jpeg;base64,"+base64Str;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
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