How to upload file field (html form) to database?

I have html form (Thymeleaf) that contains field for uploading file.

In model object, field file is set as below:

@Entity
@Table(name = "services")
public class Service {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  @Column(name = "service_id")
  private Long serviceId;

  @Size(min = 5, message = "Please enter 5 symbols or more")
  @NotBlank(message = "This field is mandatory")
  private String event;

  @NotNull(message = "This field is mandatory")
  @DateTimeFormat(pattern = "yyyy-MM-dd")
  private LocalDate created;

  @DateTimeFormat(pattern = "yyyy-MM-dd")
  private LocalDate modified;

  private BigDecimal price;

  @Lob
  private byte[] file;
  ...

Controller:

@PostMapping("/services")
  public String addEvent(
      @Valid @ModelAttribute("service") Service service,
      BindingResult bindingResult,
      Model model
  ) {
    if (bindingResult.hasErrors()) {
      return "service-add-event";
    } else {
      serviceRepository.save(service);
    }
    List<Service> services = serviceRepository.findAll();
    model.addAttribute("services", services);
    return "redirect:/services";
    }
  }

View:

  <form action="#" method="post" th:action="@{/services}" th:object="${service}">
    <div class="form-group">
      <label for="event">Event *</label>
      <input th:class="${#fields.hasErrors('event')} ? 'form-control is-invalid' : 'form-control'" 
id="event" th:field="*{event}" type="text">
      <div class="invalid-feedback" th:if="${#fields.hasErrors('event')}" th:errors="*{event}">Name Error</div>
    </div>

    ...

    <div class="form-group">
      <label for="maintenanceFile">Maintenance File</label>
      <input class="form-control" id="maintenanceFile" th:field="*{file}" type="file">
    </div>
    <button class="btn btn-primary" type="submit">Save</button>

After saving to database (H2 embedded), I see that only filename is saved to field file (for example Testfile.txt), not the whole file. Why?

How to save the whole file to database?

I've got some advises from other developers and solved this issue.

1. First, need to put enctype="multipart/form-data" into form tag.

2. Second, need to divide form objects into 2 parts. Service instance with simple fields (field file would be 'null'). And multipart input tag. This is needed, because multipart is a stream (not a field), and should be handled in Controller separately.

3. Then, in Controller we get byte array from multipart, set this bytes to Service object field, and save the instance to Repository.

Code example:

View:

<form action="#" method="post" enctype="multipart/form-data" th:object="${service}" 
th:action="@{/services}">
    <div class="form-group">
      <label for="event">Event *</label>
      <input th:class="${#fields.hasErrors('event')} ? 'form-control is-invalid' : 'form-control'"
             id="event" th:field="*{event}" type="text">
      <div class="invalid-feedback" th:if="${#fields.hasErrors('event')}" th:errors="*{event}">
        Name Error
      </div>

    (...)

    <div class="form-group">
      <label for="maintenanceFile">Maintenance File</label>
      <input class="form-control" id="maintenanceFile" name="maintenanceFile" type="file">
    </div>
    <button class="btn btn-primary" type="submit">Save</button>
    <a class="btn btn-primary" role="button"
       th:href="@{/services}">Cancel</a>
  </form>

Controller:

@PostMapping(value = "/services", consumes = {"multipart/form-data"})
  public String addEvent(
      @Valid @ModelAttribute("service") Service service,
      BindingResult bindingResult,
      @RequestParam("maintenanceFile") MultipartFile maintenanceFile,
      Model model
  ) {
    if (bindingResult.hasErrors()) {
      return "service-add-event";
    } else {
      if (!maintenanceFile.isEmpty()) {
        try {
          byte[] fileBytes = maintenanceFile.getBytes();
          service.setFile(fileBytes);
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
      serviceRepository.save(service);
      List<Service> services = serviceRepository.findAll();
      model.addAttribute("services", services);
      return "redirect:/services";
    }
  }