是否可以让空的 RequestParam 值使用 defaultValue？

Question

if I have aa request mapping similar to the following:

@RequestMapping(value = "/test", method = RequestMethod.POST)
@ResponseBody
public void test(@RequestParam(value = "i", defaultValue = "10") int i) {
}

And then call this request with:

http://example.com/test?i=

I get the error message

Failed to convert value of type 'java.lang.String' to type 'int'; nested exception is java.lang.NumberFormatException: For input string: ""'

I can solve this by either stopping the javascript client from sending empty parameters, or by accepting string values and only parsing if they are not found to be blank.

UPDATE : Later versions of spring now implement the originally desired behaviour.

I've just tested this in spring 4.3.5 and have found that the behaviour will now in fact turn the null value into the default value without raising a NumberFormatException , thus; my original mapping now works fine.

I am not sure which version of spring this behavioural change was made.

Answer 1

You could change the @RequestParam type to an Integer and make it not required. This would allow your request to succeed, but it would then be null. You could explicitly set it to your default value in the controller method:

@RequestMapping(value = "/test", method = RequestMethod.POST)
@ResponseBody
public void test(@RequestParam(value = "i", required=false) Integer i) {
    if(i == null) {
        i = 10;
    }
    // ...
}

I have removed the defaultValue from the example above, but you may want to include it if you expect to receive requests where it isn't set at all:

http://example.com/test

Answer 2

You can keep primitive type by setting default value, in the your case just add "required = false" property:

@RequestParam(value = "i", required = false, defaultValue = "10") int i

PS This page from Spring documentation might be useful: Annotation Type RequestParam

Answer 3

您可以使用泛型类Integer而不是int来设置RequestParam，它将解决您的问题。

   @RequestParam(value= "i", defaultValue = "20") Integer i

Answer 4

You can use @Nullable with default value.

@Nullable @RequestParam(value = "i", defaultValue = "10") Integer i

Answer 5

你也可以这样做 -

 @RequestParam(value= "i", defaultValue = "20") Optional<Integer> i

Answer 6

This was considered a bug in 2013: https://jira.spring.io/browse/SPR-10180

and was fixed with version 3.2.2. Problem shouldn't occur in any versions after that and your code should work just fine.