Spring MockMvc issue when validating params with custom regex validation

Hello I am no sure if this is a bug or I am not properly using MockMvc for my controller tests.

I have implemented this regex validation for my GetMapping controller which receives two String params with the follow format "YYYY-MM-DD".

@Component
public class PatterMatcher {

    private static Pattern DATE_PATTERN = Pattern.compile(
            "^((19|2[0-9])[0-9]{2})-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])$");

    public boolean matches(String date) {
        return DATE_PATTERN.matcher(date).matches();
    }
}

Then my controller makes the bellow validation before processing the request:

        boolean startDateMatch = patterMatcher.matches(startDate);
        boolean endDateMatch = patterMatcher.matches(endDate);

        if (!startDateMatch) {
            return ResponseEntity
                    .status(HttpStatus.BAD_REQUEST)
                    .body(new FailResponse("failed", "startDate format is invalid"));
        }

        if (!endDateMatch) {
            return ResponseEntity
                    .status(HttpStatus.BAD_REQUEST)
                    .body(new FailResponse("failed", "endDate format is invalid"));
        }

Thing is MockMvc always fails this validation no matters the way I construct the request. The test currently looks like this:

        LinkedMultiValueMap<String, String> parameters = new LinkedMultiValueMap<>();
        parameters.add("startDate", "2021-11-01");
        parameters.add("endDate", "2021-11-01");

        MvcResult result = mockMvc
                .perform(MockMvcRequestBuilders.get("/api/tickets").queryParams(parameters))
                .andExpect(status().isOk()).andReturn();

        System.out.println(result);

It always returns my custom ResponseEntity from my PatterMatcher regex validation:

ResponseEntity
       .status(HttpStatus.BAD_REQUEST)
       .body(new FailResponse("failed", "endDate format is invalid"));

This is the complete response:

MockHttpServletRequest:
      HTTP Method = GET
      Request URI = /api/tickets
       Parameters = {startDate=[2021-11-01], endDate=[2021-11-01]}
          Headers = []
             Body = null
    Session Attrs = {}

Handler:
             Type = com.assessment.joseassessment.controllers.TicketsController
           Method = com.assessment.joseassessment.controllers.TicketsController#getController(String, String)

Async:
    Async started = false
     Async result = null

Resolved Exception:
             Type = null

ModelAndView:
        View name = null
             View = null
            Model = null

FlashMap:
       Attributes = null

MockHttpServletResponse:
           Status = 400
    Error message = null
          Headers = [Content-Type:"application/json"]
     Content type = application/json
             Body = {"status":"failed","reason":"startDate format is invalid"}
    Forwarded URL = null
   Redirected URL = null
          Cookies = []

I suspect it is because the [] brackets on here Parameters = {startDate=[2021-11-01], endDate=[2021-11-01]} but not sure about it.

Update----------------

OK, I just added one initial "[" and one final "]" on my pattern so it matches the result output of the MockHttpServletRequest like "^\[((19|2[0-9])[0-9]{2})-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])\]$" but the validation still fails so no idea why this validation regex patter works everywhere except using MockMvc for testing.

System.out.println("[2021-11-01]".matches(
                "^\\[((19|2[0-9])[0-9]{2})-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])\\]$"));

Output = true

Thanks the great job you do.

Comment From: sbrannen

Thanks for getting in touch, but it feels like this is a question that would be better suited to Stack Overflow. As mentioned in the guidelines for contributing, we prefer to use the issue tracker only for bugs and enhancements. Feel free to update this issue with a link to the re-posted question (so that other people can find it) or add some more details if you feel this is a genuine bug.