Consider mapping empty form values to [null] for Object properties [SPR-7544]

[spring-projects-issues]

Keith Donald opened SPR-7544 and commented

Currently empty form fields are mapped to "" (empty string). This has several issues:

1. Neither a @NotNull JSR-303 constraint or a "not null" relational DB constraint fails in this case. You're left with defining a min @Size constraint or relying on a implementation-specific @NotEmpty. In addition, there is no DB min constraint you can define at the Db level. Simply mapping "" to null would solve these problems and we could just rely on @NotNull/not null.

---

Affects: 3.0.4

Issue Links:

• Formatter subsystem's ParserConverter skips parse() invocation if input string is empty [SPR-8321] #12969 Formatter subsystem's ParserConverter skips Parser invocation if input string is empty
• With binder.setRequiredFields constraint set, submitting an empty value for a required request parameter not binding an empty string to backing JavaBean [SPR-5416] #10090 With binder.setRequiredFields constraint set, submitting an empty value for a required request parameter not binding an empty string to backing JavaBean

[spring-projects-issues]

Keith Donald commented

I was able to plug in a empty String -> [null] mapping behavior by using a custom Converter<String, String>:

public class ConversionServiceFactoryBean implements FactoryBean<ConversionService> {

	public Class<?> getObjectType() {
		return ConversionService.class;
	}

	public boolean isSingleton() {
		return true;
	}

	public ConversionService getObject() throws Exception {
		FormattingConversionService conversionService = new FormattingConversionService();
		ConversionServiceFactory.addDefaultConverters(conversionService);
		conversionService.addConverter(new EmptyStringToNullConverter());
		new JodaTimeFormattingConfigurer().installJodaTimeFormatting(conversionService);			
		return conversionService;
 	}

	private static class EmptyStringToNullConverter implements Converter<String, String> {
		public String convert(String source) {
			return source.isEmpty() ? null : source;
		}
	}
}

[spring-projects-issues]

Rossen Stoyanchev commented

This relates to #10090 to the extent that #10090 expects the target field to be set to "" (rather than null) given an empty string request parameter.

[spring-projects-issues]

Keith Donald commented

There is also an inconsistency between how String fields are bound depending on if a formatter is registered or not, as pointed out by #12969 and #12038.

[spring-projects-issues]

Rossen Stoyanchev commented

A duplicate of #12038.