Spring MVC Ajax: Passing Empty Array to Ajax Controller

Question

I have the following which works well in receiving a non-empty Array,

$.ajax({
  url: "ajaxController",
  dataType: "json",
  type: "get",
  data: {
       'term': request.term,
       'exclude': ["45","66"]
  },

Controller (note the [] in RequestParam Value -- the result goes in a String[]):

public List<KeyValueBean> getChoices(String term, 
                                     @RequestParam(value = "exclude[]") 
                                        String[] exclude)  {
}

But if I pass an empty array in the same code, which sometimes happens, it breaks:

'exclude': []

or alternatively

'exclude': JSON.stringify([])

Error:

org.springframework.web.bind.MissingServletRequestParameterException: Required 
String[] parameter 'exclude[]' is not present

hamed · Accepted Answer · 2019-07-03 16:10:45Z

2

If you pay attention to the error, it says your request parameter exclude can not be null. If you need to can send empty array sometimes, you can mark your parameter as optional(not required) in this way:

@RequestParam(required = false, value = "exclude[]")

edited Jul 3, 2019 at 16:10

answered Jul 3, 2019 at 16:04

hamed

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3 Comments

gene b. Over a year ago

Yes this was the closest solution. But you have one error: You can't use value="exclude" Spring requires brackets: value="exclude[]". Once I fixed that, both cases (empty & non-empty) started working. But my question still is, I'm not passing a NULL, I'm passing an empty array. Why is Spring receiving a NULL? That's not what I want to send. If I meant a NULL, I would pass 'exclude': null.

hamed Over a year ago

This type of error is related to validation. In terms of arrays validation, null and empty array have same concept. I means, there is not any difference if you send null array or empty array! In both cases, you are violating validation rule.

gene b. Over a year ago

But the question is why Spring bound [] to a NULL. There is a difference in what I passed. I didn't pass null I passed a []. Spring could have done the String[] binding (Array of Length 0), which is what I was expecting. It's my own decision whether [] is valid while NULL is not, they should get separate binding.

unelunatriste · Accepted Answer · 2019-07-03 15:19:09Z

0

The problem is probably because you passed your @RequestParam with value="exclude[]" while you are passing the object named as "exclude".

So, it actually should be:

public List<KeyValueBean> getChoices(String term, 
                                 @RequestParam(value = "exclude") 
                                    String[] exclude)  {
}

answered Jul 3, 2019 at 15:19

unelunatriste

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