kotlin and @Valid Spring annotation

问题:

I have an entity:

class SomeInfo(
        @NotNull @Pattern(regexp = Constraints.EMAIL_REGEX) var value: String) {
    var id: Long? = null
}

And controller method:

@RequestMapping(value = "/some-info", method = RequestMethod.POST)
public Id create(@Valid @RequestBody SomeInfo someInfo) {
       ...
    }

@Valid annotation doesn't work.

It seems Spring needs a default parameterless constructor and fancy code above becomes in something ugly (but working) like this:

class SomeInfo() {

    constructor(value: String) {
            this.value = value
        }

        @NotNull @Pattern(regexp = Constraints.EMAIL_REGEX) 
        lateinit var value: String

        var id: Long? = null
    }

Any good practice to make it less wordy?

Thanks.

回答1:

Seems Spring needs these annotations to be applied to a field. But Kotlin will apply these annotations to the constructor parameter. Use field: specifier when applying an annotation to make it apply to a field. The following code should work fine for you.

class SomeInfo(
    @field:NotNull
    @field:Pattern(regexp = Constraints.EMAIL_REGEX)
    var value: String
) {
    var id: Long? = null
}

回答2:

As an alternative to Michal's answer, annotating the getter also works.

class SomeInfo(
    @get:NotNull
    @get:Pattern(regexp = Constraints.EMAIL_REGEX)
    var value: String
) {
    var id: Long? = null
}

The annoying part is, that not using @get: or @field: will annotate the constructor parameter. This is still valid kotlin code (so you don't get an error). It's just useless in these use cases.