Spring deserializes a LocalDate in a @RequestBody differently from one in a @RequestParam - why, and can they be the same?

Question

QUESTION: Spring appears to use different deserialization methods for LocalDate depending on whether it appears in a @RequestBody or a request @R

Answer 1

Create a Formatter for LocalDate:

public class LocalDateFormatter implements Formatter<LocalDate> {

    @Override
    public LocalDate parse(String text, Locale locale) throws ParseException {
        return LocalDate.parse(text, DateTimeFormatter.ISO_DATE);
    }

    @Override
    public String print(LocalDate object, Locale locale) {
        return DateTimeFormatter.ISO_DATE.format(object);
    }
}

Spring 5+: Register the formatter: Implement WebMvcConfigurer in your @Configuration and override addFormatters:

@Override
public void addFormatters(FormatterRegistry registry) {
    registry.addFormatter(new LocalDateFormatter());
}

Spring Boot: Define a @Primary @Bean to override the default formatter:

@Bean
@Primary
public Formatter<LocalDate> localDateFormatter() {
    return new LocalDateFormatter();
}

Answer 2

Per @Andreas in comments, the Spring Framework uses Jackson to deserialize @RequestBody but Spring itself deserializes @RequestParam. This is the source of the difference between the two.

This answer shows how to use @ControllerAdvice and @InitBinder to customize the deserialization of @RequestParam. The code I ultimately used follows:

import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.InitBinder;

import java.beans.PropertyEditorSupport;
import java.text.Format;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.util.function.Function;

@ControllerAdvice
public class ControllerAdviceInitBinder {

    private static class Editor<T> extends PropertyEditorSupport {

        private final Function<String, T> parser;
        private final Format format;

        public Editor(Function<String, T> parser, Format format) {

            this.parser = parser;
            this.format = format;
        }

        public void setAsText(String text) {

            setValue(this.parser.apply(text));
        }

        public String getAsText() {

            return format.format((T) getValue());
        }
    }

    @InitBinder
    public void initBinder(WebDataBinder webDataBinder) {

        webDataBinder.registerCustomEditor(
                Instant.class,
                new Editor<>(
                        Instant::parse,
                        DateTimeFormatter.ISO_INSTANT.toFormat()));

        webDataBinder.registerCustomEditor(
                LocalDate.class,
                new Editor<>(
                        text -> LocalDate.parse(text, DateTimeFormatter.ISO_LOCAL_DATE),
                        DateTimeFormatter.ISO_LOCAL_DATE.toFormat()));

        webDataBinder.registerCustomEditor(
                LocalDateTime.class,
                new Editor<>(
                        text -> LocalDateTime.parse(text, DateTimeFormatter.ISO_LOCAL_DATE_TIME),
                        DateTimeFormatter.ISO_LOCAL_DATE_TIME.toFormat()));

        webDataBinder.registerCustomEditor(
                LocalTime.class,
                new Editor<>(
                        text -> LocalTime.parse(text, DateTimeFormatter.ISO_LOCAL_TIME),
                        DateTimeFormatter.ISO_LOCAL_TIME.toFormat()));

        webDataBinder.registerCustomEditor(
                OffsetDateTime.class,
                new Editor<>(
                        text -> OffsetDateTime.parse(text, DateTimeFormatter.ISO_OFFSET_DATE_TIME),
                        DateTimeFormatter.ISO_OFFSET_DATE_TIME.toFormat()));

        webDataBinder.registerCustomEditor(
                OffsetTime.class,
                new Editor<>(
                        text -> OffsetTime.parse(text, DateTimeFormatter.ISO_OFFSET_TIME),
                        DateTimeFormatter.ISO_OFFSET_TIME.toFormat()));

        webDataBinder.registerCustomEditor(
                ZonedDateTime.class,
                new Editor<>(
                        text -> ZonedDateTime.parse(text, DateTimeFormatter.ISO_ZONED_DATE_TIME),
                        DateTimeFormatter.ISO_ZONED_DATE_TIME.toFormat()));
    }
}