<el-upload
 action="/mgr/common/imgUpload"http://這里需要配置一下文件上傳地址（跨域）
 list-type="picture-card"
 accept="image/*"
 :limit="imgLimit"
 :file-list="productImgs"
 :multiple="isMultiple"
 :on-preview="handlePictureCardPreview"
 :on-remove="handleRemove"
 :on-success="handleAvatarSuccess"
 :before-upload="beforeAvatarUpload"
 :on-exceed="handleExceed"
 :on-error="imgUploadError">
 <i class="el-icon-plus"></i>
 </el-upload>
 <el-dialog :visible.sync="dialogVisible">
 <img width="100%" :src="dialogImageUrl" alt="">
 </el-dialog>

export default {
 data() {
 return {
 dialogImageUrl: '',
 dialogVisible: false,
 productImgs: [],
 isMultiple: true,
 imgLimit: 6
 }
 },
 methods: {
 handleRemove(file, fileList) {//移除圖片
 console.log(file, fileList);
 },
 handlePictureCardPreview(file) {//預覽圖片時調用
 console.log(file);
 this.dialogImageUrl = file.url;
 this.dialogVisible = true;
 },
 
 beforeAvatarUpload(file) {//文件上傳之前調用做一些攔截限制
 console.log(file);
 const isJPG = true;
 // const isJPG = file.type === 'image/jpeg';
 const isLt2M = file.size / 1024 / 1024 < 2;
 
 // if (!isJPG) {
 // this.$message.error('上傳頭像圖片只能是 JPG 格式!');
 // }
 if (!isLt2M) {
  this.$message.error('上傳圖片大小不能超過 2MB!');
 }
 return isJPG && isLt2M;
 },
 handleAvatarSuccess(res, file) {//圖片上傳成功
 console.log(res);
 console.log(file);
 this.imageUrl = URL.createObjectURL(file.raw);
 },
 handleExceed(files, fileList) {//圖片上傳超過數量限制
 this.$message.error('上傳圖片不能超過6張!');
 console.log(file, fileList);
 },
 imgUploadError(err, file, fileList){//圖片上傳失敗調用
 console.log(err)
 this.$message.error('上傳圖片失敗!');
 }
 }
 }

 @RequestMapping(value = "/imgUpload")
 public Wrapper imgUpload(HttpServletRequest req, MultipartHttpServletRequest multiReq)
  throws IOException {
 System.out.println("---" + fileUploadPath);//我這里用的springboot 在application.properties中配置，使用@Value 獲取的文件上傳目錄
 
 MultipartFile file = multiReq.getFile("file");
 String originalFilename = file.getOriginalFilename();
 String suffix = originalFilename.substring(originalFilename.indexOf("."));
 String localFileName = MD5Util.md5(file.getInputStream()) + suffix;
 File localFile = new File(fileUploadPath + localFileName);
 if (!localFile.exists()) {
  localFile.createNewFile();
 
  FileOutputStream fos = new FileOutputStream(
   localFile);
  FileInputStream fs = (FileInputStream) multiReq.getFile("img").getInputStream();
  byte[] buffer = new byte[1024];
  int len = 0;
  while ((len = fs.read(buffer)) != -1) {
  fos.write(buffer, 0, len);
  }
  fos.close();
  fs.close();
 
 } else {
  log.info("文件已存在！！");
 }
 
 return WrapMapper.wrap(
  Wrapper.SUCCESS_CODE,
  Wrapper.SUCCESS_MESSAGE,
  "http://localhost:8080/img/" + localFileName);//這里是我執行封裝的返回結果，也可以使用map,
 }

import java.io.*;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
 
public class MD5Util {
 
 private static char[] Digit = {'0', '1', '2', '3', '4', '5', '6', '7', '8',
  '9', 'a', 'b', 'c', 'd', 'e', 'f'};
 
 public static String getMd5Sum(String inputStr)
  throws NoSuchAlgorithmException {
 MessageDigest digest = MessageDigest.getInstance("MD5");
 byte[] inputStrByte = inputStr.getBytes();
 digest.update(inputStrByte, 0, inputStrByte.length);
 
 byte[] md5sum = digest.digest();
 
 StringBuffer sb = new StringBuffer();
 for (int i = 0; i < 16; i++) {
  char[] ob = new char[2];
  ob[0] = Digit[md5sum[i] >> 4 & 0x0F];
  ob[1] = Digit[md5sum[i] & 0x0F];
  String s = new String(ob);
  sb.append(s);
 }
 
 return sb.toString();
 }
 
 /**
 * 對字符串進行 MD5 加密
 *
 * @param str
 *  待加密字符串
 *
 * @return 加密后字符串
 */
 public static String md5(String str) {
 MessageDigest md5 = null;
 try {
  md5 = MessageDigest.getInstance("MD5");
  md5.update(str.getBytes("UTF-8"));
 } catch (NoSuchAlgorithmException e) {
  throw new RuntimeException(e.getMessage());
 } catch (UnsupportedEncodingException e) {
  throw new RuntimeException(e.getMessage());
 }
 byte[] encodedValue = md5.digest();
 int j = encodedValue.length;
 char finalValue[] = new char[j * 2];
 int k = 0;
 for (int i = 0; i < j; i++) {
  byte encoded = encodedValue[i];
  finalValue[k++] = Digit[encoded >> 4 & 0xf];
  finalValue[k++] = Digit[encoded & 0xf];
 }
 
 return new String(finalValue);
 }
 
 /**
 * 簽名字符串
 *
 * @param text
 *  需要簽名的字符串
 * @param sign
 *  簽名結果
 * @return 簽名結果
 */
 public static boolean verify(String text, String sign) {
 String mysign = md5(text);
 if (mysign.equals(sign)) {
  return true;
 } else {
  return false;
 }
 }
 
 /**
 * 對文件進行 MD5 加密
 *
 * @param file
 *  待加密的文件
 *
 * @return 文件加密后的 MD5 值
 * @throws IOException
 */
 public static String md5(File file) throws IOException {
 FileInputStream is = new FileInputStream(file);
 return md5(is);
 
 }
 
 
 public static String md5(InputStream inputStream) throws IOException {
 
 MessageDigest md5 = null;
 try {
  md5 = MessageDigest.getInstance("MD5");
  int n = 0;
  byte[] buffer = new byte[1024];
  do {
  n = inputStream.read(buffer);
  if (n > 0) {
   md5.update(buffer, 0, n);
  }
  } while (n != -1);
  inputStream.skip(0);
 } catch (NoSuchAlgorithmException e) {
  throw new RuntimeException(e.getMessage());
 } finally {
  inputStream.close();
 }
 
 byte[] encodedValue = md5.digest();
 
 int j = encodedValue.length;
 char finalValue[] = new char[j * 2];
 int k = 0;
 for (int i = 0; i < j; i++) {
  byte encoded = encodedValue[i];
  finalValue[k++] = Digit[encoded >> 4 & 0xf];
  finalValue[k++] = Digit[encoded & 0xf];
 }
 return new String(finalValue);
 }
}