Document how SpEL defaulting syntax differs from PropertyPlaceholder defaulting [SPR-7674]

[spring-projects-issues]

Daniel Hopper opened SPR-7674 and commented

Currently there is support for default values with @Value when using property place holders

@Value("${fee:25}")
private int overdraft;

But this doesn't work with SPeL expressions. While this isn't inherently an issue at this point I think this will be problematic with the new features in Spring 3.1 for the Environment configuration profiles.

public class SpelExpressionDefaultTest {

	@Test
	public void testSpelDefaultValue() {
		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(
			PropertyPlaceholderConfigurer.class, FeeService.class
		);
		
		Assert.assertEquals(25, ctx.getBean(FeeService.class).getOverdraft());
	}
	
	@Component
	public static class FeeService {
		@Value("#{systemProperties['fee']:25}")
		private int overdraft;

		public int getOverdraft() {
			return overdraft;
		}
	}
}

This particular test will fail on a parsing exception from SPeL. This directly relates to #11472 which was closed as invalid as there is a work around to just use ${:default} syntax instead.

If we change the FeeService to

@Component
public static class FeeService {
	@Value("${fee:25}")
	private int overdraft;

	public int getOverdraft() {
		return overdraft;
	}
}

This will work as expected. SPeL should probably support the default value option especially with the new Environment Profiles coming in 3.1

---

Affects: 3.0.4

Referenced from: commits f20ded5

[spring-projects-issues]

Daniel Hopper commented

Thinking about this a little more I did test the following expression using the Elvis Operator and it does work this way.

@Value("#{systemProperties['fee']?:25}")

So I guess this then does function as it should in terms of defaults, but maybe the documentation should be updated to show this.