Spring Boot传递MultipartFile至服务器的序列化问题求助

在Spring Boot项目中，尝试通过服务器将文件存入数据库，选择用MultipartFile传递文件，但遇到序列化错误：

Caused by: jakarta.ws.rs.client.ResponseProcessingException: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class java.io.ByteArrayInputStream and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: org.springframework.mock.web.MockMultipartFile["inputStream"])
Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class java.io.ByteArrayInputStream and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: org.springframework.mock.web.MockMultipartFile["inputStream"])

已在application.properties中添加spring.jackson.serialization.FAIL_ON_EMPTY_BEANS=false，但问题依旧。Gradle构建已成功，Postman测试上传功能正常，但客户端代码调用失败。

相关代码如下：

客户端ServerUtils代码 #

public void saveFile(File file) throws IOException {
        internalPostRequest("secure/" + store.accessStore().getUsername() + "/file/add",
                Entity.entity(convert(file), APPLICATION_JSON), new GenericType<>(){});
    }
public static MultipartFile convert(File file) throws IOException {
        String filename = file.getName();
        FileInputStream inputStream = new FileInputStream(file);
        return new MockMultipartFile(filename, inputStream);
    }
private <T> T internalPostRequest(String path, Entity send, GenericType<T> retType) {
        return ClientBuilder.newClient(new ClientConfig())
                .target(getServer()).path(path)
                .request(APPLICATION_JSON)
                .accept(APPLICATION_JSON)
                .post(send, retType);
    }

服务端FileController代码 #

public class FileController {
    @Autowired
    private StorageService service;
    @PostMapping("/add")
    public ResponseEntity<?> uploadFile(@RequestParam("file") MultipartFile file) throws IOException {
        String uploadFile = service.uploadFile(file);
        return ResponseEntity.status(HttpStatus.OK)
                .body(uploadFile);
    }
}

服务端StorageService代码 #

@Service
public class StorageService {
    @Autowired
    private StorageRepository repository;

    public String uploadFile(MultipartFile file) throws IOException {
        repository.save(new FileData(file.getOriginalFilename(),
                file.getContentType(), compressFile(file.getBytes())));
        return "File uploaded succesfully: "+ file.getOriginalFilename();
    }
    public String getType(String fileName){
        Optional<FileData> dbFileData = repository.findByName(fileName);
        if (dbFileData.isPresent()) {
            return dbFileData.get().getType();
        } else {
            return "File not found: " + fileName;
        }
    }
    public static byte[] compressFile(byte[] data) {
        Deflater deflater = new Deflater();
        deflater.setLevel(Deflater.BEST_COMPRESSION);
        deflater.setInput(data);
        deflater.finish();

        ByteArrayOutputStream outputStream = new ByteArrayOutputStream(data.length);
        byte[] tmp = new byte[4*1024];
        while (!deflater.finished()) {
            int size = deflater.deflate(tmp);
            outputStream.write(tmp, 0, size);
        }
        try {
            outputStream.close();
        } catch (Exception ignored) {
        }
        return outputStream.toByteArray();
    }
}

核心问题分析 #

客户端错误地将MultipartFile以APPLICATION_JSON格式发送，Jackson尝试序列化MockMultipartFile内部的ByteArrayInputStream，而该类没有可序列化的属性，导致报错。Postman正常是因为它用的是multipart/form-data格式，符合服务端@RequestParam("file")的接收要求。

修复步骤 #

1. 客户端改用multipart/form-data格式发送请求
   不要直接序列化MultipartFile，而是构建multipart表单数据。修改客户端saveFile和internalPostRequest方法：

   public void saveFile(File file) throws IOException {
       // 构建multipart表单
       FormDataMultiPart formData = new FormDataMultiPart();
       // 将文件转为InputStream，添加到表单中
       try (FileInputStream fis = new FileInputStream(file)) {
           formData.field("file", fis, MediaType.MULTIPART_FORM_DATA_TYPE, file.getName());
           internalPostRequest("secure/" + store.accessStore().getUsername() + "/file/add",
                   Entity.entity(formData, MediaType.MULTIPART_FORM_DATA_TYPE), new GenericType<>(){});
       }
   }
   
   private <T> T internalPostRequest(String path, Entity send, GenericType<T> retType) {
       return ClientBuilder.newClient(new ClientConfig())
               .target(getServer()).path(path)
               .request(MediaType.APPLICATION_JSON) // 接收JSON响应
               .post(send, retType);
   }
   

2. 移除无效配置（可选）
   之前添加的spring.jackson.serialization.FAIL_ON_EMPTY_BEANS=false对这个问题无效，可以从application.properties中删除，因为问题根源不是空Bean序列化，而是错误的请求格式。

3. 优化文件转换逻辑（可选）
   客户端不需要创建MockMultipartFile对象，直接用文件流构建multipart表单即可，可移除原有的convert方法。

验证 #

修改后重新调用客户端的saveFile方法，即可正常上传文件，不会再出现序列化错误。

内容的提问来源于stack exchange，提问作者Micu Bogdan