POC to reattach MultipartFiles to objects

[cromoteca]

This POC adds some preliminary code to reattach MultipartFiles to arbitrary objects.

It has been tested with this service:

public record Customer(String name, List<Order> orders) {}
public record Order(List<String> items, MultipartFile invoice) {}

public String uploadCustomer(Customer customer) {
    System.out.format("Uploaded customer `%s` with %d orders\n", customer.name(), customer.orders().size());
    for (Order order : customer.orders()) {
        System.out.format("Order with %d items and invoice `%s` with size %d\n",
                order.items().size(),
                order.invoice().getOriginalFilename(),
                order.invoice().getSize());
    }
    return "Uploaded customer " + customer.name();
}

and this request:

POST http://localhost:8080/connect/HelloEndpoint/uploadCustomer HTTP/1.1
Host: localhost:8080
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:134.0) Gecko/20100101 Firefox/134.0
Accept: application/json
Accept-Language: en-GB,en;q=0.8,fr-FR;q=0.6,fr;q=0.4,it;q=0.2
Accept-Encoding: gzip, deflate, br, zstd
Content-Type: multipart/form-data;boundary=----MYBOUNDARY
Referer: http://localhost:8080/
X-CSRF-Token: e44c315f-b825-4057-ba5f-2967ed167c71
Origin: http://localhost:8080
DNT: 1
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-origin
Connection: keep-alive
Cookie: Idea-ca342cc6=93254400-1659-49ba-9b12-282fb6325c2b; JSESSIONID=04D782331CAE64FB18EED57A754B7661; csrfToken=e44c315f-b825-4057-ba5f-2967ed167c71
Priority: u=0
Pragma: no-cache
Cache-Control: no-cache

------MYBOUNDARY
Content-Disposition: form-data; name="data"
Content-Type: application/json

{
  "customer": {
    "name": "John Doe",
    "orders": [
      {
        "items": [
          "apple",
          "banana"
        ]
      },
      {
        "items": [
          "grape",
          "orange",
          "pear"
        ]
      }
    ]
  }
}
------MYBOUNDARY
Content-Disposition: form-data; name="/customer/orders/0/invoice"; filename="invoice1.txt"
Content-Type: text/plain

invoice of the first order
------MYBOUNDARY
Content-Disposition: form-data; name="/customer/orders/1/invoice"; filename="invoice2.txt"
Content-Type: text/plain

invoice of the second order
------MYBOUNDARY--

The idea is that the request will contain one part which has no filename and is of type application/json. This is the ordinary object.

Then, the other parts are supposed to have a filename and a name that is used as path in the JSON, using the path syntax that Jackson uses internally.

Related to #3130

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.65%. Comparing base (b241ce6) to head (891d775).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3165   +/-   ##
=======================================
  Coverage   92.65%   92.65%           
=======================================
  Files          85       85           
  Lines        3187     3187           
  Branches      778      778           
=======================================
  Hits         2953     2953           
  Misses        182      182           
  Partials       52       52           

Flag	Coverage Δ
unittests	92.65% <ø> (ø)

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[cromoteca]

To be clear, this also works for top-level parameters:

public String uploadAvatar(String user, MultipartFile file) {
    return String.format("The avatar for %s is %d bytes.\n", user, file.getSize());
}

Request follows:

POST http://localhost:8080/connect/HelloEndpoint/uploadAvatar HTTP/1.1
Host: localhost:8080
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:134.0) Gecko/20100101 Firefox/134.0
Accept: application/json
Accept-Language: en-GB,en;q=0.8,fr-FR;q=0.6,fr;q=0.4,it;q=0.2
Accept-Encoding: gzip, deflate, br, zstd
Content-Type: multipart/form-data;boundary=----MYBOUNDARY
Referer: http://localhost:8080/
X-CSRF-Token: e44c315f-b825-4057-ba5f-2967ed167c71
Origin: http://localhost:8080
DNT: 1
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-origin
Connection: keep-alive
Cookie: Idea-ca342cc6=93254400-1659-49ba-9b12-282fb6325c2b; JSESSIONID=04D782331CAE64FB18EED57A754B7661; csrfToken=e44c315f-b825-4057-ba5f-2967ed167c71
Priority: u=0
Pragma: no-cache
Cache-Control: no-cache

------MYBOUNDARY
Content-Disposition: form-data; name="data"
Content-Type: application/json

{
  "user": "John"
}
------MYBOUNDARY
Content-Disposition: form-data; name="/file"; filename="avatar.png"
Content-Type: image/png

iVBORw0KGgoAAAANSUhEUgAAACAAAAAgCAMAAABEpIrGAAAABGdBTUEAALGPC/xhBQAAAAFzUkdCAdnJLH8AAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAAAZQTFRFAAAA/wAAG/+NIgAAAAF0Uk5TAEDm2GYAAABsSURBVDjLvZNLCgAhDEOT+196GBgY2yYGXJhl+qz9KNDFV/DiJ+GXeCV+jxJYTEqCWil+ATA1yk67M4h4AptbiyHLkglaCgYgdJ4BbgfDMcc+2rEJjJTc6GSZ4c0aALY++6vOAaS4/7oNWY0H7vQCVCaU9zAAAAAASUVORK5CYII=
------MYBOUNDARY--

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud