如果上传时未指定类型，如何通过SpringBoot从PostGRES数据库加载和显示文档？

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

<dependency>
    <groupId>org.postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <version>版本号</version>
</dependency>

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Document {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String fileName;
    private byte[] content;
    private String contentType;

    // 省略构造函数、getter和setter方法
}

import org.springframework.data.jpa.repository.JpaRepository;

public interface DocumentRepository extends JpaRepository<Document, Long> {
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.http.MediaType;

import java.io.IOException;
import java.util.List;

@RestController
@RequestMapping("/documents")
public class DocumentController {

    @Autowired
    private DocumentRepository documentRepository;

    @PostMapping
    public void uploadDocument(@RequestParam("file") MultipartFile file) throws IOException {
        Document document = new Document();
        document.setFileName(file.getOriginalFilename());
        document.setContent(file.getBytes());
        document.setContentType(file.getContentType());
        documentRepository.save(document);
    }

    @GetMapping("/{id}")
    public ResponseEntity<byte[]> getDocument(@PathVariable("id") Long id) {
        Document document = documentRepository.findById(id).orElse(null);
        if (document != null) {
            return ResponseEntity.ok()
                    .contentType(MediaType.parseMediaType(document.getContentType()))
                    .body(document.getContent());
        } else {
            return ResponseEntity.notFound().build();
        }
    }

    @GetMapping
    public List<Document> getAllDocuments() {
        return documentRepository.findAll();
    }
}