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Three new article modules: configuration binding, profiles and config data, Spring AOP

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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
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Ankur Mhatre
2026-09-08 16:36:17 +00:00
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# @ConfigurationProperties vs @Value
Companion project for [**@ConfigurationProperties vs @Value in Spring Boot 4**](https://ankurm.com/)
on ankurm.com.
Every table and transcript quoted in that article was produced by running something here.
Three of them were produced twice, because the first answer was wrong — see
[chapter 2](docs/02-relaxed-binding.md).
## Versions
| | |
|---|---|
| Spring Boot | 4.1.1 |
| Spring Framework | 7.0.9 |
| JDK | Eclipse Temurin 25.0.4.1 (LTS) |
| Validation | Hibernate Validator via `spring-boot-starter-validation` |
## Quickstart
```bash
export JAVA_HOME=/path/to/jdk-25
mvn -DskipTests package
./scripts/run-all.sh # regenerate every transcript in docs/output/
mvn test # 7 contract tests
```
## Profiles
| Profile | What it does |
|---|---|
| *(none)* | binds `demo.*` from `application.yaml` |
| `probe` | runs the relaxed-binding matrix and exits |
| `envprobe` | reports one property as seen by the binder and by `@Value` |
| `badvalidation` | values that violate every constraint, so startup fails |
| `csvlist` | the recipients list as a comma-separated string |
## Endpoints
| Endpoint | Purpose |
|---|---|
| `GET /diag/bound` | the bound objects, and the same values via `@Value` |
| `GET /diag/origin?name=` | every source holding a property, in precedence order, with file and line |
Both are diagnostics. Delete them before shipping.
## Documentation
1. [Two mechanisms, not two styles](docs/01-two-mechanisms.md)
2. [Relaxed binding, measured](docs/02-relaxed-binding.md)
3. [Getting the bean registered](docs/03-registration.md)
4. [Records, constructor binding and defaults](docs/04-records-and-defaults.md)
5. [Validation](docs/05-validation.md)
6. [When `@Value` is still the right answer](docs/06-when-value-still-wins.md)
7. [IDE metadata, and the JDK 23 change that silently breaks it](docs/07-ide-metadata.md)
8. [Diagnosing a value](docs/08-diagnosing-a-value.md)
## Captured output
| File | Produced by |
|---|---|
| [`00-versions.txt`](docs/output/00-versions.txt) | `scripts/demo-versions.sh` |
| [`01-relaxed-matrix.txt`](docs/output/01-relaxed-matrix.txt) | `scripts/demo-relaxed-matrix.sh` |
| [`02-env-var-binding.txt`](docs/output/02-env-var-binding.txt) | `scripts/demo-env-binding.sh` |
| [`03-value-vs-binding.txt`](docs/output/03-value-vs-binding.txt) | `scripts/demo-value-vs-binding.sh` |
| [`04-validation-failure.txt`](docs/output/04-validation-failure.txt) | `scripts/demo-validation.sh` |
| [`05-metadata-generation.txt`](docs/output/05-metadata-generation.txt) | `scripts/demo-metadata-generation.sh` |
## Three findings worth the trip
- **`@Value` gets relaxed binding inside Spring Boot.** The universal claim that it does not is
a statement about the Spring Framework; Boot attaches a property source that changes it.
- **The configuration processor silently stops on JDK 23+** when declared as a plain
dependency, so IDE auto-completion quietly dies while the build stays green.
- **`@Valid` is not what makes nested constraints run.** Boot's `ValidationBindHandler`
validates every object it binds.