写一个spring boot vue 用户头像上传代码

好的，以下是一个简单的 Spring Boot + Vue.js 项目中用户头像上传的代码。

前端代码：

<template>
  <div>
    <img :src="imageUrl" :alt="username" width="100">
    <form>
      <input type="file" @change="onFileChange" accept="image/*">
      <button type="button" @click="upload">上传头像</button>
    </form>
  </div>
</template>

<script>
import axios from 'axios';

export default {
  data() {
    return {
      imageUrl: '',
      username: 'test'
    }
  },
  methods: {
    onFileChange(e) {
      const file = e.target.files[0];
      this.imageUrl = URL.createObjectURL(file);
      this.file = file;
    },
    upload() {
      const formData = new FormData();
      formData.append('file', this.file);
      formData.append('username', this.username);
      axios.post('/api/upload', formData).then(response => {
        console.log(response.data);
      }).catch(error => {
        console.log(error);
      });
    }
  }
}
</script>

后端代码：

@RestController
@RequestMapping("/api")
public class UserController {
  @Autowired
  private UserService userService;

  @PostMapping(value = "/upload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
  public ResponseEntity<Object> uploadFile(@RequestParam("file") MultipartFile file,
                                            @RequestParam("username") String username) {
    try {
      User user = userService.getUserByUsername(username);
      if (user != null) {
        String fileName = StringUtils.cleanPath(file.getOriginalFilename());
        String fileExtension = fileName.substring(fileName.lastIndexOf("."));
        String newFileName = UUID.randomUUID().toString() + fileExtension;
        String uploadDir = "uploads/";
        String filePath = uploadDir + newFileName;
        FileUploadUtil.saveFile(uploadDir, newFileName, file);
        user.setAvatar(filePath);
        userService.saveUser(user);
        return ResponseEntity.ok().body("File uploaded successfully!");
      } else {
        return ResponseEntity.badRequest().body("User not found!");
      }
    } catch (Exception ex) {
      return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(ex.getMessage());
    }
  }
}

其中，`FileUploadUtil` 是一个工具类，用于保存上传的文件到服务器。`UserService` 是一个服务类，用于处理与用户相关的业务逻辑。`User` 是一个实体类，用于映射数据库中的用户表。