Ankur Mhatre
86246dc860
configuration-properties/ @ConfigurationProperties vs @Value on Spring Boot 4.1.1. The relaxed-binding matrix is generated by binding each spelling rather than transcribed, and re-checked against real processes -- the in-process probe was wrong twice before it was right. Records the three findings that came out of it: @Value does get relaxed resolution inside Spring Boot (Boot attaches ConfigurationPropertySources), the configuration processor silently stops generating metadata on JDK 23+ when declared as a plain dependency, and @Valid is not what makes nested constraints run. profiles-and-config/ Precedence, profiles, spring.config.import and config trees. /precedence reports every source holding a property in rank order with file and line, which turns "my profile file had no effect" into a two-line answer. Also pins the counterintuitive one: an imported file outranks the file that imported it. spring-aop/ Designators, proxy types, and aspects that do not fire. One advice per supported designator so the reference table is generated from real matches; all fourteen unsupported designators fed to the parser. Two corrections to the reference documentation: unsupported designators throw UnsupportedPointcutPrimitiveException (extends RuntimeException, not IllegalArgumentException), and spring-boot-starter-aop was renamed to spring-boot-starter-aspectj in Boot 4. 19 contract tests across the three modules, 15 captured transcripts, all regenerated by scripts/run-all.sh. Verified on Spring Boot 4.1.1, Spring Framework 7.0.9, JDK 25.0.4.1. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Gip4srpzMwjgoba6uEfbr5
46 lines
1.9 KiB
Markdown
46 lines
1.9 KiB
Markdown
[← Relaxed binding](02-relaxed-binding.md) · [Index](../README.md) · [Records and defaults →](04-records-and-defaults.md)
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# 3. Getting the bean registered
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`@ConfigurationProperties` on a class does nothing on its own. The class has to become a bean,
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and there are three ways to arrange that:
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| How | Where it goes | When to use it |
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|---|---|---|
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| `@ConfigurationPropertiesScan` | on the application class | most applications; scans a package |
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| `@EnableConfigurationProperties(Foo.class)` | on any `@Configuration` class | libraries, or when you want the list explicit |
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| `@Component` | on the properties class itself | works, but mixes a stereotype into a value type |
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This project uses `@ConfigurationPropertiesScan`, on
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[`ConfigBindingApplication`](../src/main/java/com/ankurm/configprops/ConfigBindingApplication.java).
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## The failure
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If none of the three is present, the class compiles, the application starts, and the bean does
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not exist. Injecting it fails with `NoSuchBeanDefinitionException` — which is at least loud.
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The quiet version is worse: with constructor binding, a properties *record* that is never
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registered simply never appears, and if the only thing that used it was optional, nothing
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complains at all.
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## Constructor binding and `@Autowired` do not mix
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A type bound through its constructor is built by the binder, not by the container. It cannot
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have collaborators injected into that constructor, because every parameter is treated as a
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property to bind. If a properties type needs a collaborator, it is not a properties type.
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## `@ConfigurationProperties` on an `@Bean` method
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Legal, and useful when the type comes from a library you cannot annotate:
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```java
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@Bean
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@ConfigurationProperties(prefix = "demo.thirdparty")
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ThirdPartyConfig thirdPartyConfig() {
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return new ThirdPartyConfig();
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}
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```
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This uses setter binding, not constructor binding — the object already exists by the time the
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binder sees it.
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