Highlight that Duration and Period conversion is provided by the ApplicationConversionService and, by default, is not available for web conversion

[jamestrandung]

Version: Spring Boot 2.3.2

I have the following simple TestController.

@RestController
@RequestMapping("/test")
public class TestController {
    @Getter
    protected static class TestObj {
        @DurationUnit(ChronoUnit.MINUTES)
        private Duration breakTime;
    }

    @GetMapping("/test")
    public void test(@RequestBody TestObj test) {
        System.out.println(test.getBreakTime());
    }
}

With the following body...

{
    "breakTime" : 30
}

... what I see in the console is

PT30S

Obviously, conversion is not happening. It always default to SECONDS.

[wilkinsona]

@DurationUnit is supported by the ApplicationConversionService that's used for configuration property binding. A separate conversion service, WebConversionService, is used for conversions when receiving requests and sending responses so you won't get any @DurationUnit support for web requests/responses.

It looks like we need to clarify the documentation

[jamestrandung]

@wilkinsona Thank you for the clarification. Does that also mean we don't have any support for Duration as of now in WebConversionService and Spring Boot in general. I do see other annotations/classes like DurationFormat and DurationStyle. Not sure if it can do the job.

[wilkinsona]

Looking more closely at your code snippet, I've also just realised that the WebConversionService won't be involved either. When you are receiving JSON, Jackson is used to convert the JSON into a Java object. It has its own deserialisers for turning, for example, a JSON string into a Duration.

DurationFormat and DurationStyle are used the customise the behaviour of the Duration-related converters that are registered with the ApplicationConversionService. If you want to use these for web conversion as well (for request parameters, form binding, etc), you can use a WebMvcConfigurer and the configure method on ApplicationConversionService to set it up:

@Bean
WebMvcConfigurer conversionConfigurer() {
	return new WebMvcConfigurer() {

		@Override
		public void addFormatters(FormatterRegistry registry) {
			ApplicationConversionService.configure(registry);
		}

	};
}