Controller:

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

import cn.tedu.store.controller.ex.FileEmptyException;
import cn.tedu.store.controller.ex.FileIOException;
import cn.tedu.store.controller.ex.FileSizeException;
import cn.tedu.store.controller.ex.FileStateException;
import cn.tedu.store.controller.ex.FileTypeException;
import cn.tedu.store.entity.User;
import cn.tedu.store.service.IUserService;
import cn.tedu.store.util.JsonResult;

@RestController
@RequestMapping("users")
public class UserController  {

   @Autowired
   private IUserService service;



   @RequestMapping("change_password")
   public JsonResult<Void> changePassword(@RequestParam("old_password") String oldPassword, @RequestParam("new_password") String newPassword,HttpSession session){

      // 从session中获取uid
      Integer uid=Integer.valueOf(session.getAttribute(SESSION_UID).toString());

      // 从session中获取username
      String username=session.getAttribute(SESSION_USERNAME).toString();

      service.changePassword(uid,oldPassword,newPassword,username);
      return new JsonResult<Void>(SUCCESS);
   }

   private static final long AVATAR_MAX_SIZE=1*1024*1024;
   private static final List<String> AVATAR_TYPES=new ArrayList<String>();

   // 静态初始化器：用于初始化本类的静态成员
   static {
      AVATAR_TYPES.add("image/jpeg");
      AVATAR_TYPES.add("image/png");
   }


   @PostMapping("change_avatar")
   public JsonResult<String> changeAvatar(@RequestParam("file") MultipartFile file,
             HttpServletRequest request,HttpSession session){

      // 空文件验证
      if(file.isEmpty()) {
         throw new FileEmptyException("文件上传异常！文件不能为空");
      }
      // 文件大小验证
      long fileSize=file.getSize();
      if(fileSize>AVATAR_MAX_SIZE) {
         throw new FileSizeException("文件上传异常！文件大小超过上限:"+(AVATAR_MAX_SIZE/1024)+"kb");
      }

      // 文件类型验证
      if(!AVATAR_TYPES.contains(file.getContentType())) {
         throw new FileTypeException("文件上传异常！文件类型不正确，允许的类型有："+AVATAR_TYPES);
      }


      // 生成文件名
      String oFilename=file.getOriginalFilename();
      Integer index=oFilename.lastIndexOf(".");
      String suffix="";
      if(index!=-1) {
         suffix=oFilename.substring(index);
      }
      String filename=UUID.randomUUID().toString()+suffix;

      // 生成目标路径
      String filePath=request.getServletContext().getRealPath("upload");
      File parent=new File(filePath);
      if(!parent.exists()) {
         parent.mkdirs();//创建对应的目录
      }

      File dest=new File(parent,filename);
      // 将用户上传的头像保存到服务器上
      try {
         file.transferTo(dest);
      } catch (IllegalStateException e) {
         throw new FileStateException("文件上传异常！"+e.getMessage());
      } catch (IOException e) {
         throw new FileIOException("文件上传异常！"+e.getMessage());
      }

      // 将头像在服务器的路径保存到数据库
      String avatar="/upload/"+filename;
      Integer uid=getUidFromSession(request.getSession());
      String username=getUsernameFromSession(request.getSession());
      service.changeAvatar(uid,avatar,username);
      JsonResult<String> jr=new JsonResult<>(SUCCESS);
      jr.setData(avatar);
      return jr;
      // return new JsonResult<String>(SUCCESS, avatar);
   }
Service:

@Override
public void changeAvatar(Integer uid, String avatar, String modifiedUser)
      throws UserNotFoundException, UpdateException {
   // 使用uid查询用户数据
   User user=mapper.findByUid(uid);
   // 判断返回结果是否为null
   if(user ==null) {
      // 是：UserNotFoundException
      throw new UserNotFoundException("上传头像异常！用户数据不存在");
   }

   // 判断isDelete是否为1
   if(user.getIsDelete().equals(1)) {
      // 是：UserNotFoundException
      throw new UserNotFoundException("上传头像异常！用户数据不存在"); 
   }

   // 更新用户头像
   Integer row=mapper.updateAvatar(uid, avatar, modifiedUser, new Date());
   // 判断受影响的行数是否不为1
   if(!row.equals(1)) {
      // 是：UpdateException
      throw new UpdateException("上传头像异常！请联系管理员");
   }
}