我成功地使用multipart上传了一个文件，并将实体类ID附加到了文件中。发送get请求返回空值。
这是我的帖子终结点：

@PostMapping("/{id}/upload_multiple")
public ResponseEntity<ResponseMessage> createDocument(@PathVariable Long id,
        @RequestParam("applicationLetter") MultipartFile appLetter,
        @RequestParam("certificateOfInc") MultipartFile cInc, @RequestParam("paymentReceipt") MultipartFile payment,
        @RequestParam("taxClearance") MultipartFile tax, @RequestParam("staffsResume") MultipartFile staffs,
        @RequestParam("letterOfCredibility") MultipartFile credibility,
        @RequestParam("workCertificate") MultipartFile workCert,
        @RequestParam("consentAffidavit") MultipartFile affidavit,
        @RequestParam("collaborationCert") MultipartFile colabo, @RequestParam("directorsId") MultipartFile idcard,
        @RequestParam("membership") MultipartFile member) throws IOException {

    documentService.create(id, appLetter, cInc, payment, tax, staffs, credibility, workCert, affidavit, colabo,
            idcard, member);
    String message = "Upload successful";

    return ResponseEntity.status(HttpStatus.OK).body(new ResponseMessage(message));
}

上传的文件保存在另一个文件夹10001中，文件夹10001是文档实体的ID。我现在的挑战是从10001文件夹中获取这些文件。

这是我所尝试的，但对所有文档都返回空值：

@GetMapping( "/files/{filename:.+}/{id}")
public ResponseEntity<Resource> getFile(@PathVariable String filename) {
    Resource file = documentService.load(filename);
    return ResponseEntity.ok()
            .contentType(MediaType.parseMediaType("application/octet-stream"))
            .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.getFilename() + "\"")
            .body(file);
}

我的服务类别：

private final Path root = Paths.get("documents");

 @Override
  public Resource load(String filename) {
    try {
      Path file = root.resolve(filename);
      Resource resource = new UrlResource(file.toUri());

      if (resource.exists() || resource.isReadable()) {
        return resource;
      } else {
        throw new RuntimeException("Could not read the file!");
      }
    } catch (MalformedURLException e) {
      throw new RuntimeException("Error: " + e.getMessage());
    }
  }

我的实体类：

@Entity
@Getter
@Setter
public class Documents {

    @Id
    @Column(nullable = false, updatable = false)
    @SequenceGenerator(
            name = "primary_sequence",
            sequenceName = "primary_sequence",
            allocationSize = 1,
            initialValue = 10000
    )
    @GeneratedValue(
            strategy = GenerationType.SEQUENCE,
            generator = "primary_sequence"
    )
    private Long id;

    @Column(nullable = false)
    private String applicationLetter;

    @Column(nullable = false)
    private String certOfIncorporation;

    @Column(nullable = false)
    private String paymentReceipt;

    @Column(nullable = false)
    private String taxClearance;

    @Column(nullable = false)
    private String staffsResume;
}